2933413 Stoichiometry Mole Concept for Iitjee

MASTERING PHYSICAL CHEMISTRY By-- S.K.SINHA

B-7. JAWAHAR NAGAR.Main Road ,Kota. Ph-0744-2422383 .Mo-93149-05055

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Moles Concept, What is a Mole?

Since atoms and molecules are so tiny, it is convenient to talk about a large number of them at a time. The chemical counting unit is known as the mole. A mole is defined as the amount of substance that contains as many elementary entities (atoms, molecules, or other particles) as there are atoms in exactly 12 g of the 6

12C isotope. It has been found experimentally that

1 mole of particles = 6.022 x 1023 particlesThis value is known as Avogadro�s number. Just like 1 dozen of anything always contains 12 items, 1 mole of anything always contains 6.022 x 1023 items.

Atomic Mass and Molar Mass Isotopic masses cannot be obtained by summing the masses of the elementary particles (neutrons, protons, and electrons) from which the isotope is formed. This process would give masses slightly too large, since mass is lost when the neutrons and protons come together to form the nucleus. Atomic masses (also called atomic weights) are thus assigned relative to the mass of a particular carbon isotope, 6

12C , which is assigned the mass of 12 amu exactly. Likewise 1 mole of 612C has a mass of

exactly 12 g. Atomic masses and molar masses of other isotopes are calculated based on their mass relative to that of Carbon-12. Masses of �average� atoms are found by summing isotopic masses, weighting each isotopic mass by its abundance . Thus one �average� C atom has a mass of 12.01 amu, and the mass of 1 mole of �average� carbon atoms has a mass of 12.01 g. These average masses are what are given on the periodic chart.

Molecular Masses and Compound Masses Molecular masses are found by summing atomic masses . They are often called molecular weights. Thus the mass of 1 mole of water, H2O, would be 2 x (molar mass of H) plus 1x (molar mass of O) or [(2 x 1.008 g) + (1 x 16.00 g)] = 18.02 g. Ionic compounds such as NaCl do not contain molecules. Their formulas give the relative numbers of each kind of atom in the sample. What we mean by the molar mass (or the molecular weight) of an ionic compound is really the formula weight. The formula weight is the sum of the atomic masses in the formula.

Percent Composition of Compounds The percent composition by mass is the percent by mass of each element in a compound. If there are n moles of an element per mole of compound, the percent by mass of the element is calculated using the equation,

% Composition of Element =n molar mass of element

molar mass of compound

100%

The sum of the % compositions of all elements in a compound is 100%. Exercises

1. The atomic mass scale gives masses in atomic mass units (amu) relative to the mass of carbon-12. (a) What is the mass of one 12C atom in atomic mass units (amu)? (b) What is the mass of an average C atom in atomic mass units (amu)? (c) What is the mass of an average Cl atom in amu? (d) What is the mass of an average Br atom in amu? 2. The molar mass scale gives masses in grams (g) relative to the mass of 12C. (a) What is the mass in grams of 1 mole (mol) of 12C? (b) What is the mass in grams of 1 mole (mol) of carbon? (c) What is the mass in grams of 1 mole (mol) of Cl? (d) What is the mass in grams of 1 mole (mol) of Na? 3. How many 12C atoms are present in a mole of 12C ? 4. Cinnamic alcohol is used mainly in perfumery, particularly in soaps and cosmetics. Its molecular formula is C9H10O. (a) Calculate the percent composition by mass of C, H, and O in cinnamic alcohol.

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(b) How many molecules of cinnamic alcohol are contained in a sample of mass 0.469 g? Answers: 1. (a) 12 amu exactly; (b) 12.01 amu; (c) 35.45 amu; (d) 79.90 amu. 2. (a) 12 g exactly; (b) 12.01 g; (c) 35.45 g; (d) 22.99 g. 3. 6.022 x 1023 atoms of 12C. 4. (a) 80.56% C; 7.51% H; 11.93% O; (b) 2.11 x 1021 molecules of C9H10O.

Empirical and Molecular Formulas The empirical formula of a compound gives the simplest whole number ratio of different types of atoms in the compound. All salt formulas are empirical formulas. On the other hand, the molecular formula of a compound may or may not be the same as its empirical formula. For example, the molecular formula of butane is C4H10 while its empirical formula is C2H5. The molecular formula gives the true number of each kind of atom in a molecule.

Empirical formulas may be easily determined from experimental data.

Usually you must first determine how many grams of each type of atom are in the compound. If percent composition data is given, assume that you have 100.0 g of the compound; then the number of grams of each element is equal to the percentage for that element.

The next task is convert the grams of each element to moles of the element. Be sure to keep at least three significant figures in your answers.

The final step is to write the molar amounts of each element as subscripts in the formula. Then divide all molar subscripts by the smallest value in the set. At this point, the subscripts may all be very close to whole numbers; if so, you are finished. If one (or more) of the subscripts is not close to a whole number, multiply all molar subscripts by the simple factor which makes all subscripts whole numbers.

Once the empirical formula is determined, the molecular formula is easily found if the molar mass (molecular weight) of the molecule is also known. You first calculate the molar mass of the empirical formula. Then you divide the molar mass of the molecule by the molar mass of the empirical formula. The division should give a simple whole number. That number is the factor by which all subscripts in the empirical formula must be multiplied to obtain the molecular formula.

Exercises

1. The molecular formula of the antifreeze ethylene glycol is C2H6O2. What is the empirical formula?

2. A well-known reagent in analytical chemistry, dimethylglyoxime, has the empirical formula C2H4NO. If its molar mass is 116.1 g/mol, what is the molecular formula of the compound?

3. Nitrogen and oxygen form an extensive series of oxides with the general formula NxOy. One of them is a blue solid that comes apart, reversibly, in the gas phase. It contains 36.84% N. What is the empirical formula of this oxide?

4. A sample of indium chloride weighing 0.5000 g is found to contain 0.2404 g of chlorine What is the empirical formula of the indium compound?

Answers: 1. CH3O 2. Molar mass of empirical formula is 58.06 g/mol. Thus molecular formula is C4H8N2O2. 3. The ratios are N1.00O1.50 . Since 1.50 is not close to a whole number, we multiply both subscripts by 2. The empirical formula is thus N2O3. (The name is dinitrogen trioxide.) 4. InCl3.

Chemical Stoichiometry Problems Calculating the yield of a chemical reaction is a process at the heart of chemistry. While there are many ways a problem can be phrased, in all cases the stoichiometric coefficients in the balanced reaction are used to determine the mole ratios between reactants and products. Thus the first step is usually



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calculating the moles of each species available. If an amount is given in grams, the molar mass is used as a conversion factor to change grams to moles.

Limiting Reagent Problems In some problems, amounts of more than one species are given. In that case your first task is to determine which species is the limiting reagent. Just as you can make only 1 bicycle from 2 wheels and 4 handlebars (with 3 handlebars left over), and only 2 bicycles from 8 wheels and 2 handlebars (with 4 wheels left over), in chemical reactions some species are limiting while others may be present in excess.

In the case of a bicycle, we need 2 wheels

1 handlebar

. We obtain analogous information about the relative

amounts of species that react from the stoichiometric coefficients in a balanced chemical equation. For example, in Exercise (2) below the equation CO(g) + 2 H2(g) CH3OH (l)

tells us we need 2 mol H2

1 mol CO

. If we have more than 2 moles of H2 for each mole of CO, CO will be the

limiting reagent and the excess H2 will not react. Conversely, if we have more than 1 mole of CO for every 2 moles of H2, H2 will be the limiting reagent and the excess CO(g) will be left over. In each case, the yield of CH3OH is determined by the moles of limiting reagent available.

Calculating the Theoretical Yield The theoretical (maximum possible) yield is based on the amount of limiting reagent available. The yield is calculated in steps:

�Calculate moles of all reactants available. If amounts are given in grams, convert grams to moles using

the molar mass of each reactant as your conversion factor: 1 mole reactant

# g reactant

.

�NOTE: Skip this step if you have already identified the limiting reagent. To determine which reagent is limiting, use the mole ratio obtained from the balanced equation for the reaction to find the moles of reactant B needed to react with the available moles of reactant A. If the moles of B available are less than the moles of B needed, reactant B is the limiting reagent and reactant A is in excess. Conversely, if the moles of B available are more than the moles of B needed, A is the limiting reagent and B is in excess.

�Calculate the moles of product based on the moles of limiting reagent available; use the stoichiometric

ratio of # moles product

# moles limiting reagent

as the conversion factor.

�If you are asked for the yield in grams, convert the yield in moles to a yield in grams using the molar

mass as your conversion factor: # g product

1 mole product

Percent Yield Most reactions do not go to completion, and so the actual yield is less than the percent yield. The percent yield is calculated as

Percent yield =actual yield

theoretical yield

100%

Exercises: 1. Ammonia is produced by the reaction 3 H2(g) + N2(g) 2 NH3(g) (a) If N2(g) is present in excess and 55.6 g of H2(g) reacts, what is the theoretical yield of NH3(g)? (b) What is the percent yield if the actual yield of the reaction is 159 g of NH3(g)? Answers: 1(a) 313 g NH3(g); (b) 50.8% yield. 2. Methyl alcohol (wood alcohol), CH3OH, is produced via the reaction CO(g) + 2 H2(g) CH3OH (l) Answers: 2(a) CO is the limiting reagent; (b) 8.52 g CH3OH; (c) 0.13 g H2; (d) 88.3%



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Limiting Reagent Problems Limiting reagent problems are simple to recognize as the initial amounts of more than one species will be given. For instance, for the reaction:

2H2(g) + O2(g) 2H2O If the amounts of both H2 and O2 are given, then this is a limiting reagent problem; otherwise, this is not a limiting reagent problem. There are 6 steps to a limiting reagent problem: 1. Convert the amounts of all species to moles 2. Divide the number of moles of each reactant species by its stoichiometric coefficient. The smallest number corresponds to the limiting reagent. 3. Determine the moles of all other species that react or form by multiplying the smallest number from step 2 by each species' stoichiometric coefficient. 4. Add/Subtract the moles determined in step 3 to/from the initial moles. 5. Convert moles to amounts 6. Check to make sure that total initial mass = total final mass Problem-1..In the reaction Mg3N2 + 6H2O 3Mg(OH)2 + 2NH3, if the initial amount of Mg3N2 is 58.1g and the initial amount of H2O is 20.4g, what are the final masses of each specie? 1. Convert the amounts of all species to moles MM(Mg3N2) = 100.93 g Mg3N2 / mol Mg3N2 mass(Mg3N2) = 58.1 g Mg3N2 x (1 mol Mg3N2 / 100.93 g Mg3N2) = 0.576 mol Mg3N2 MM(H2O) = 18.02 g H2O / mol H2O mass(H2O) =20.4 g H2O x (1 mol H2O / 18.02 g H2O) = 1.13 mol H2O

Compound Mg3N2 H2O Mg(OH)2 NH3

MM 100.93 18.02 58.32 17.03

Initial Mass 58.1 g 20.4 g 0.0 g 0.0 g

Initial Moles 0.576 mol Mg3N2

1.13 mol H2O 0.0 mol Mg(OH)2

0.0 mol NH3

1. Divide the number of moles of each reactant species by its stoichiometric coefficient. The smallest amount is the limiting reagent.

Step 2 Division 0.576 mol / 1 = 0.576 mol

1.13 mol / 6 = 0.189 mol� SMALLEST NUMBER SO LIMITING REAGENT

1. Determine the amount of all other species that react or form by multiplying the smallest number from step 2 by each species stoichiometric coefficient.

Step 2 Division 0.576 mol / 1 = 0.576 mol


Step 3 Amounts 1 x 0.189 mol = 0.189 mol

Mg3N2

6 x 0.189 mol = 1.13 mol

H2O

3 x 0.189 mol = 0.566 mol

Mg(OH)2

2 x 0.189 mol = 0.377 mol NH3

1. Add/Subtract the amounts determined in step 3 to/from the initial amounts.

Final Moles

0.576 mol - 0.189 mol = 0.387 mol

Mg3N2

1.13 mol - 1.13 mol =

0.0 mol H2O

0.0 mol + 0.566 mol = 0.566 mol Mg(OH)2

0.0 mol + 0.377 mol = 0.377 mol

NH3

1. Convert moles to amounts



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Final Mass

0.387 mol x 100.93 g/mol

= 39.1 g Mg3N2

0.0 g

0.566 mol x 58.32 g/mol =

33.0 g Mg(OH)2

0.377 mol x 17.03 g/mol =

6.42 g NH3

1. Check to make sure that total initial mass = total final mass 2. + 20.4 = 78.5; 39.1 + 33.0 + 6.42 = 78.5�Mass is conserved! Problem 2.-In the reaction Au2S3 + 3H2 3H2S + 2Au, if the initial amount of Au2S3 is 500.20 g and the initial amount of H2 is 5.67g, what are the final masses of each specie? 1. Convert the amounts of all species to moles MM(Au2S3) =490.15 g Au2S3 / mol Au2S3 mass(Au2S3) =500.20 g Au2S3x (1 mol Au2S3/ 490.15 g Au2S3) = 0.1.0204 mol Au2S3 MM(H2) = 2.02 g H2/ mol H2 mass(H2) =5.67 g H2x (1 mol H2/ 2.02 g H2) = 2.8125 mol H2

Compound Au2S3 H2 H2S Au

MM 490.15 2.02 34.09 196.97

Initial Mass 500.20 g 5.67 g 0.0 g 0.0 g

Initial Moles 1.0204 mol Au2S3

2.8125 mol H2 0.0 mol H2S 0.0 mol Au


Step 2 Division 1.0204 mol / 1 = 1.0204

mol



Step 3 Amounts 1 x 0.9375

mol = 0.9375 mol Au2S3

3 x 0.9375 mol = 2.8125

mol H2

3 x 0.9375 mol = 2.8125

mol H2S

2 x 0.9375 mol = 1.875 mol Au


Final Moles

1.0204 mol - 0.9375 mol = 0.08288 mol

Au2S3

2.8125 mol - 2.8125 mol =

0.0 mol H2

0.0 mol + 2.8125 mol = 2.8125 mol

H2S

0.0 mol + 1.875 mol = 1.875 mol

Au


Final Mass

0.08288 mol x 490.15

g/mol = 40.6 g Au2S3

0.0 g 2.8125 mol x 34.09 g/mol =

95.9 g H2S

1.875 mol x 196.97 g/mol =

369.4 g Au

1. Check to make sure that total initial mass = total final mass 500.20 + 5.67 = 505.87; 40.6 + 95.9 + 369.4 = 505.9�Mass is conserved! Problem-3-In the reaction 2C3H6 + 2NH3 + 3O2 2C3H3N + 6H2O, if the initial amounts are C3H6 22.5g, NH3 20.6 g, and O2 18.1 g, what are the final amounts of each specie? 1. Convert the amounts of all species to moles



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Compound C3H6 NH3 O2 C3H3N H2O

MM 42.078 17.034 32.000 53.064 196.97

Initial Mass 22.5 g 20.6 g 18.1 g 0.0 g 0.0 g

Initial Moles 0.5347 mol C3H6

1.2094 mol NH3

0.5656 mol O2

0.0 mol C3H3N

0.0 mol H2O


Step 2 Division

0.5347 mol / 2 =0.2675

mol

1.2094 mol / 2 = 0.6047

mol



Step 3 Amounts

2 x 0.1885 mol =

0.3771 mol C3H6

2 x 0.1885 mol =

0.3771 mol NH3

3 x 0.1885 mol =

0.5656 mol O2

2 x 0.1885 mol =

0.3771 mol C3H3N

6 x 0.1885 mol

=1.1313 mol H2O


Final Moles

0.5347 - 0.3771 =

0.1576 mol C3H6

1.2094 - 0.3771 =

0.8323 mol NH3

0.5656 - 0.5656 = 0.0

mol O2

0.0 + 0.3771 = 0.3771

mol C3H3N

0.0 + 1.1313 =

1.1313 mol H2O

Final Mass


Final Mass

0.1576 mol x (42.078 g

/mol) = 6.6 g C3H6

0.8323 mol x (17.034 g/mol) =

14.2 g NH3

0.0 g O2

0.3771 x (53.064 g/mol) = 20.0 g C3H3N

1.1313 x (18.016 g/mol) =

20.4 g H2O

1. Check to make sure that total initial mass = total final mass 22.5 + 20.6 + 18.1 = 61.2; 6.6 + 14.2 + 20.0 +20.4 = 61.2g�Mass is conserved! Now why do steps 2 and 3 give the correct results? Give a reaction aA +bB cC + dD, we know that a moles of A will react with b moles of B to give c moles of C and d moles of D. This means, for instance, that Y moles of A will require Y mol A x (b mol B / a mol A) = Yb/a mol B, since the stoichiometric coefficients are conversion factors between different species. We define 1 mol of this reaction as the process of mixing a mol of A with b mol of B to form c mol C and d mol D. Thus, if we have Y mol of A, we can convert to mol of reaction by Y x (1 mol reaction / a mol A) = Y/a. Thus, the divisions in step 2 convert each initial amount into units of mol reaction and, hence, calculate the amount of the reaction that each reactant can permit. The smallest of these amounts is then the least amount of reaction that any initial amount of a reactant will allow. Step 3 is then converting from units of mol reaction to mol of a species by multiplying by Z mol reaction x (c mol C / 1 mol reaction), .



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Rules for Working Limiting Reagent Problems Determine the number of moles of each reactant.

Find the number of moles of desired product that can be produced by each reactant.

The limiting reagent is the one that produces the smallest amount of that product.

The amount of product produced by that limiting reagent is the final answer. Convert to grams if necessary.



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Problem Solving In Solutions Concentrations of Solutions There are a number of ways to express the relative amounts of solute and solvent in a solution. This page describes calculations for four different units used to express concentration: Percent Composition (by mass) Molarity Molality Mole Fraction

Percent Composition (by mass) We can consider percent by mass (or weight percent, as it is sometimes called) in two ways: The parts of solute per 100 parts of solution. The fraction of a solute in a solution multiplied by 100. We need two pieces of information to calculate the percent by mass of a solute in a solution: The mass of the solute in the solution. The mass of the solution. Use the following equation to calculate percent by mass:

Molarity

Molarity tells us the number of moles of solute in exactly one liter of a solution. (Note that molarity is spelled with an "r" and is represented by a capital M.) We need two pieces of information to calculate the molarity of a solute in a solution: The moles of solute present in the solution. The volume of solution (in liters) containing the solute. To calculate molarity we use the equation:

Molality

Molality, m, tells us the number of moles of solute dissolved in exactly one kilogram of solvent. (Note that molality is spelled with two "l"'s and represented by a lower case m.) We need two pieces of information to calculate the molality of a solute in a solution: The moles of solute present in the solution. The mass of solvent (in kilograms) in the solution. To calculate molality we use the equation:

Mole Fraction

The mole fraction, X, of a component in a solution is the ratio of the number of moles of that component to the total number of moles of all components in the solution. To calculate mole fraction, we need to know: The number of moles of each component present in the solution. The mole fraction of A, XA, in a solution consisting of A, B, C, ... is calculated using the

equation: To calculate the mole fraction of B, XB, use:



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MOLE AND PERCENT WORKSHEET . 1. C2H2 is the molecular formula for ethylyne ( acetylene). (a) How many atoms are in one molecule? (b) Which atoms make up acetylene? (c) How many moles of atoms are in one molecule of acetylene? (d) How many molecules are in 5.3 moles of acetylene? (e) How many atoms are in a mole of acetylene? 2. Calculate the molar mass of a mole of the following materials: (a) Al (b) Ra (c) Co (d) CO (e) CO2 (f) HCl (g) Na2CO3 (h) Ca(NO3)2 (i) (NH4)3(PO4) (j) H2O (k) Epsom salts - Mg(SO4)·7H2O (m) blue vitriol - Cu(SO4)·5H2O ? 3. Calculate the number of moles in: (a) 2.3 # of carbon (b) 0.014 g of Tin (c) a 5 Oz silver bracelet (d) a pound of table salt (e) a 350 kg cast iron engine block (f) a gal. of water (8.3 #) (g) a ton of sand (SiO2) (h) 6.2 grams of blue vitriol (i) a pound of Epsom salts ? 4. Calculate the number of atoms in: (a) 100 g of Argon (b) 1.21 kg aluminum foil (c) a 28 # lead brick (d) the E7 kg of water in an olympic swimming pool (e) 7 kg of hydrogen gas (f) a tonne of calcium nitrate ? 5. What is the percentage composition of oxygen in each of the following materials: (a) CO (b) CO2 (c) (NO3)

- (d) isopropyl alcohol C3H8O (e) calcium nitrate (f) blue vitriol - Cu(SO4)·5H2O ? 6. What is the percentage composition of phosphate in each of the following materials: (a) phosphoric acid 7. What is the percentage composition of sulfate in each of the following materials: (a) sulfuric acid (b) sodium sulfate (c) Epsom salts ( d) aluminum sulfate ?

ANSWERS 1a. 4 b. C & H c. 6.64 E-24 d. 3.1922 E24 e. 2.4092 E24

2a. 27.0 b. 226.0 c. 58.9 d. 28.0 e. 44.0

f. 36.5 g. 106.0 h. 164.1 i. 149.0 j. 18.0

k. 246.4 m. 249.6 3a. 86.9 b. 1.18 E-4 c. 1.31

d. 7.75 e. 6.27 E3 f. 210 g. 1.51 E4 h. 0.0248

i. 1.84 4a. 1.51 E24 b. 2.69 E25 c. 3.69 E25 d. 1.00 E33 e. 4.22E27 f. 3.30 E28 5a. 57.1% b. 72.7% c. 77.4%

d. 26.7% e. 58.5% f. 57.7% 6a. 96.9% b. 0%

c. 63.8% d. 61.2% 7a. 98.0% b. 67.6% c. 39.0%

d. 84.2%



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Multiple Choice Question Set 1 1. The density of chlorine relative to air is

(a) 2.44 (b) 3 (c) found experimentally (d) 4

2. A gaseous oxide contains 30.4% of nitrogen, one molecule of which contains one nitrogen atom.

The density of the oxide relative to oxygen is

(a) 0.94 (b) 1.44 (c) 1.50 (d) 3.0

3. The mass of an oxygen atom is half that of a sulphur atom. Can we decide on this basis that the

density of sulphur vapour relative to oxygen is 2?

(a) Yes (b) No

4. Density of air is 0.001293 g/cc. Its vapour density is

(a) 0.001293 (b) 1.293 (c) 14.48 (d) cannot be calculated

5. 5.6 litres of oxygen at NTP is equivalent to

(a) 1 mole (b) ½ mole (c) 1/4 mole (d) 1/8 mole

6. 22.4 litres of water vapour at NTP, when condensed to water, occupies an approximate volume of

(a) 18 litres (b) 1 litre (c) 1 mL (d) 18 mL

7. Which of the following has the highest mass ?

(a) 1g-atom of C (b) 1/2 mole of CH4 (c) 10 mL of water (d) 3.011 × 1023 atoms of O

8. 6.022 × 1022 molecules of N2 at NTP will occupy a volume of

(a) 22.4 litres (b) 2.24 litres (c) 6.02 litres (d) 6.02 mL

9. How many grams are contained in 1 gram-atom of Na ?

(a) 13 g (b) 23 g (c) 1g (d) 1/23 g

10. The weight of 350 mL of a diatomic gas at 0°C and 2 atm pressure 1 g. The wt. of one atom is

(a)

19108 6 022

108

. .

16N (b)

32N (c) 16N (d) 32N

11. The number of atoms present in 16 g of oxygen is

(a) 6.02 × 1011.5 (b) 3.01 × 1023 (c) 3.01 × 1011.5 (d) 6.02 × 1023

12. 1 mole of a compound contains 1 mole of C and 2 moles of O. The moleculr wt of the compound is

(a) 3 (b) 12 (c) 32 (d) 44

13. The volume of a gas at 0°C and 700 mm pressure is 760 cc. The number of molecules present in

this volume is

(a) 1.88 × 1022 (b) 6.022 × 1023 (c) 18.8 × 1023 (d) 18.8 × 1022

14. 1 mole of a diatomic element X2 contains 34 and 40 moles of electrons and neutrons respectively.

The isotopic formula of the element is

(a) 3474 X (b) 17

37 X (c) 3440 X (d) 20

40 X

15. 2 moles of H atoms at NTP occupy a volume of

(a) 11.2 litres (b) 44.8 litres (c) 2 litres (d) 22.4 litres

16. No. of electrons in 1.8 mL of H2O(l) is

(a) 6.02 × 1023 (b) 3.011 × 1023 (c) 0.6022 × 1023 (d) 60.22 × 1023

17. Moleculear weight of a gas, 11.2 litres of which at NTP weighs 14 g. is

(a) 14 (b) 28 (c)

14112. (d) 14 × 11.2



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18. The weight of 1 mole of a gas of density 0.1784 g/L at NTP is

(a) 0.1784g (b) 1 g (c) 4 g (d) cannot be calculated

19. Number of HCl molecules preent in 10 mL of 0.1 N HCl solution is

(a) 6.022 × 1023 (b) 6.022 × 1022 (c) 6.022 × 1021 (d) 6.022 × 1020

20. Number of atoms in 12 gm of 612 C is

(a) 6 (b) 12 (c) 6.022 × 1023 (d) 12 × 6.022 × 1023

21. 5 moles of a gas in a closed vessel was heated from 300 K to 600 K. The pressure of the gas

doubled. The numbe of moles of the gas will be

(a) 5 (b) 2.5 (c) 10 (d) 20

22. Which of the following contains the greatest number of oxygen atoms ?

(a) 1g of O (b) 1g of O2 (c) 1g of O3 (d) All have the same no of atoms

23. If the atomic weight of carbon were set at 24 amu, the value of the Avogadro constant would be

(a) 6.022 × 1023 (b) 12.044 × 1023 S (c) 1 × 1023 s (d) none of these

24. 24If 32 g of O2 contains 6.022 × 1023 molecules at NTP then 32 g of S, under the same conditions,

will contain,

(a) 6.022 × 1023 S (b) 3.011 × 1023 S (c) 12.044 × 1023S (d) 1 × 1023 S

25. How many moles of electrons weigh one kilogram ?

(a) 6.022 × 1023 (b)

19108

1031

.

(c) 6 0229108

1054..

(d)

19108 6 022

108

. .

Answer To Multiple Choice Question Set 1

1 2 3 4 5 6 7 8 9 10 a b b C c d a b b a 11 12 13 14 15 16 17 18 19 20 d d a B d a b c d c 21 22 23 24 25 a d b A d



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Multiple Choice Question Set 2 1. If 16 grams of O2 react with excess C2H6, how many grams of CO2 will be formed? The formula mass of O2 = 32 amu and the formula mass of CO2 = 44 amu. The balanced chemical equation is...

(a) 22 grams (b)13 grams (c)9 grams (d)7 grams 2. If 64 grams of O2 react with 45 grams of C2H6, how many grams of CO2 will be formed? The formula mass of O2 = 32 amu, C2H6 = 30 and the formula mass of CO2 = 44 amu. The balanced chemical equation is given in the previous problem. (a) 132 grams (b)66 grams (c)50 grams (d)44 grams 3. How many milliliters of 2 M NaCl solution are required to make 1 liter of 0.4 M NaCl solution? (a) 5,000 mL (b)800 mL (c)200 mL (d)0.2 mL 4. If an air bag in a car needs 44.8 L of gas when filled, how many grams of NaN3 are needed to fill the bag with nitrogen gas at standard temperature and pressure? Remember that one mole of any gas will occupy 22.4 L at STP. The balanced chemical reaction is...

(a) 56 grams (b)87 grams (c)130 grams (d)1.3 grams 5. How many grams of NaOH are needed to make 100 milliliters of a 0.2 molar solution of NaOH? (a) 0.02 grams (b)0.8 grams (c)20 grams (d)800 grams 6. How many grams of NaHCO3 (baking soda) would you need to neutralize 500 mL of battery acid (H2SO4) that has been spilled on your garage floor? Assume that the concentration of the battery acid is 12 molar. The balanced chemical equation is...

(a) 1,008,000 grams (b)1,008 grams (c)504 grams (d)252 grams 7. When 157.0 grams of CaSO4 are dissolved in enough water to yield a volume of 7.25x102 milliliters of solution. The molarity of this solution will be... (a) 0.0016 M (b)0.837 M (c)1.15 M (d)1.59 M 8. How many grams of carbon are needed to completely react with 75.2 g of SiO2? The balanced

chemical equation is... (a) 3.76 g (b)15.1 g (c)36.0 g (d)45.1 g 9. How many milliliters of 4.00 M NaOH must be added to 100.0 mL of 0.2000 M H2SO4 solution to completely neutralize the acid? The balanced chemical equation is...

(a) 0.04 mL (b)5.0 mL (c)10.0 mL (d)500 mL 10. In an acid-base titration, 42.90 mL of 0.825 M H2SO4 was required to neutralize 75.0 mL of NaOH solution. What is the molarity of the NaOH solution? The balanced chemical equation is given in the previous problem. (a) 0.0009 M (b)0.071 M (c)0.472 M (d)0.944 M 11. If you react 1.00 L of ethane at STP with 3.00 L of oxygen at STP, how many grams of carbon dioxide will be formed? One mole of any gas occupies 22.4 L at STP. The balanced chemical equation

is... (a) 1.96 g (b)3.37 g (c)3.93 g (d)5.89 g



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12. What is the percent yield of water if 0.90 g of water is obtained when 29.0 g of butane is burned in excess oxygen? The balanced chemical equation is...

(a) 0.02% (b)2% (c)10% (d)36% 13. One of the functions of the catalytic converter in your car is to oxidize carbon monoxide to carbon dioxide. If 15.0 g of carbon monoxide reacts with 9.0 g of oxygen, how many grams of which compound remains unreacted? The balanced chemical equation is...

(a) 0.4 g of oxygen remains unreacted (b)0.8 g of carbon monoxide remains unreacted (c) 7.1 g of carbon monoxide remains unreacted (d) 8.1 g of oxygen remains unreacted

Multiple Choice Question Set 3 1. Consider the unbalanced chemical equation, F2 + H2O OF2 + HF. When the reaction is balanced with smallest integer coefficients, the coefficient for H2O is

a. 1 b.2 c.3 d.4

2. Consider the unbalanced chemical equation, Al(OH)3 + H2CO3 Al2(CO3)3 + H2O. When the reaction is balanced with smallest integer coefficients, the coefficient for H2CO3 is

a. 1 b.2 c.3 d.5

3. Consider the unbalanced chemical equation, CaCO3 + H3PO4 Ca3(PO4)2 + CO2 + H2O. When the reaction is balanced with smallest integer coefficients, the coefficient for CO2 is

a. 1 b.3 c.5 d.7

4. Consider the unbalanced chemical equation for the complete combustion of butanoic acid (C4H8O2): C4H8O2 + O2 CO2 + H2O. When the reaction is balanced using smallest integer coefficients, the coefficient for O2 is

a. 3 b.4 c.5 d.6

5. Ammonia (NH3) reacts with oxygen to produce nitrogen oxide (NO) and water. If this reaction is described with a balanced chemical equation using smallest integer coefficients, the coefficient for nitrogen oxide is

a. 1 b.2 c.3 d.4

6. Propene gas (C3H6) burns completely in oxygen to produce carbon dioxide and water as the only products. If this reaction is described with a balanced chemical equation using smallest integer coefficients, the coefficient for water is

a. 1 b.3 c.6 d.9

7. The complete combustion of liquid toluene (C7H8) in oxygen yields just carbon dioxide and water. When this reaction is balanced using smallest integer coefficients, the coefficient for water is

a. 2 b.4 c.8 d.12

8. The complete combustion of liquid propyl alcohol (C3H7OH) in oxygen yields just carbon dioxide and water. When this reaction is balanced using smallest integer coefficients, the coefficient for O2 is

a. 5 b.9 c.10 d.20

9. If the reaction, K2O2(s) + H2O(l) KOH(aq) + O2(g), is balanced using smallest integer coefficients, and these coefficients are interpreted as moles, what is the total mass of the reactants?

a. 128 g b.146 g c.238 g d.256 g

10. The complete combustion of gaseous ethane (C2H6) in oxygen yields just carbon dioxide and water. When this reaction is balanced using smallest integer coefficients, and these coefficients are interpreted as moles, what is the total mass of the reactants?

a. 62 g b.126 g c.142 g d.284 g

11. Consider the unbalanced reaction for the oxidation of sugar (sucrose) by potassium chlorate,



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KClO3(s) + C12H22O11(s) KCl(s) + CO2(g) + H2O(g). When this reaction is balanced, the number of moles of KClO3 needed to react completely with one mole of C12H22O11 is

a. 2 b.4 c.8 d.12

12. When the reaction, MnO2(s) + HCl(aq) MnCl2(aq) + Cl2(g) + H2O(l), is balanced, the number of moles of Cl2 produced from 1.00 mol MnO2 and excess HCl is

a. 1 b.2 c.4 d.8

13. In the balanced chemical reaction, XeF4(g) + 2 H2O(g) Xe(g) + 4 HF(g) + O2(g), what mass of water is required to react completely with 10.0 g of XeF4?

a. 0.87 g b.1.20 g c.1.74 g d.2.40 g

14. Zinc sulfide (ZnS) reacts with oxygen to form zinc oxide (ZnO) and gaseous sulfur dioxide (SO2). What mass of SO2 is produced by the complete conversion of 10.0 g of ZnS to ZnO?

a. 3.29 g b.5.00 g c.8.35 g d.10.0 g

15. A crystalline compound of formula Mg(NO3)2�6H2O loses some of its water of hydration when it is heated, but undergoes no other chemical changes. When a 10.0 g sample is heated in this way, the residue weighs 7.19 g. What is the formula of the residue?

a. Mg2(NO3)2�11H2O b.Mg(NO3)2�4H2O

c. Mg(NO3)2�3H2O d.Mg(NO3)2�2H2O e.Mg(NO3)2�H2O

16. Potassium chlorate (KClO3) is a solid that decomposes on heating above 400°C. 7.394 g of KClO3 is subjected to prolonged heating above 400°C, after which the residue is found to weigh 4.498 g. A possible formula for the residue is

a. KCl b.KO c.KO2

d.KClO e.KClO2

17. A 3.05-g sample of an alloy of gold (Au) and copper is reacted with excess nitric acid (HNO3) to form 4.00 g of copper (II) nitrate (Cu(NO3)2). Thus the percentage of Au in the alloy, by mass, is

a. 11.9% b.33.6% c.44.4% d.55.6%

18. Assume that the following reaction between phosphorus and chlorine gas goes as far as possible to give the product, gaseous phosphorus pentachloride.P4(s) + 10 Cl2(g) 4 PCl5(g)

If 0.231 mol of P4 is reacted with an excess of Cl2, how much PCl5 will be produced?

a. 0.231 mol b.0.462 mol c.0.693 mol d.0.924 mol

19. Assume that the following reaction between phosphorus and chlorine gas goes as far as possible to give the product, gaseous phosphorus pentachloride.P4(s) + 10 Cl2(g) 4 PCl5(g). What volume of PCl5 will be produced by the reaction of 129 L of chlorine gas with excess P4, if all gas volumes are measured under the same conditions of temperature and pressure.

a. 322 L b.129 L c.51.6 L d.4.00 L

20. Assume that the following reaction between phosphorus and chlorine gas goes as far as possible to give the product, gaseous phosphorus pentachloride.P4(s) + 10 Cl2(g) 4 PCl5(g)

if 1.239 g of P4 is combined with 0.0893 mol of chlorine gas, what is the theoretical yield of PCl5?

a.0.0179 mol b.0.0357 mol c.0.0400 mol d.0.0893 mol

21. Consider the production of ammonia gas through the reaction of nitrogen with hydrogen as described by the balanced equation,N2(g) + 3 H2(g) 2 NH3(g)

How much N2 would be required to react completely with 1.50 mol of H2?

a. 14.0 g b.28.0 g c.42.0 g d.126 g

22. Consider the production of ammonia gas through the reaction of nitrogen with hydrogen as described by the balanced equation, N2(g) + 3 H2(g) 2 NH3(g)

How much NH3 would be produced by the complete reaction of 8.91 g of H2 with excess N2?

a. 25.1 g b.50.2 g c.75.3 g d.100 g



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23. Consider the production of ammonia gas through the reaction of nitrogen with hydrogen as described by the balanced equation, N2(g) + 3 H2(g) 2 NH3(g) If all gas volumes are measured under the same conditions of pressure and temperature, what volume of ammonia gas would be produced by the complete reaction of 40.0 L of nitrogen?

a. 20.0 L b.26.7 L c.40.0 L d.80.0 L

24. Consider the reaction between hydrogen sulfide gas (H2S) and oxygen to produce sulfur dioxide gas (SO2) and water according to the balanced equation, 2 H2S(g) + 3 O2(g) 2 SO2(g) + 2 H2O(l). All gas volumes are assumed to be measured under the same fixed conditions of temperature and pressure. How much H2S will be required to react completely with 6.11 g of O2?

a. 2.71 g b.4.34 g c.6.51 g d.8.68 g

25. Consider the reaction between hydrogen sulfide gas (H2S) and oxygen to produce sulfur dioxide gas (SO2) and water according to the balanced equation, 2 H2S(g) + 3 O2(g) 2 SO2(g) + 2 H2O(l). All gas volumes are assumed to be measured under the same fixed conditions of temperature and pressure. What volume of SO2 can be produced from the complete reaction of 8.9 L of O2?

a. 2.00 L b.3.00 L c.8.9 L d.13.4 L

26. Consider the reaction between hydrogen sulfide gas (H2S) and oxygen to produce sulfur dioxide gas (SO2) and water according to the balanced equation, 2 H2S(g) + 3 O2(g) 2 SO2(g) + 2 H2O(l). All gas volumes are assumed to be measured under the same fixed conditions of temperature and pressure.If 2.50 L of H2S and 3.00 L of O2 are allowed to react completely, how much SO2 will be produced?

a. 2.00 L b.2.50 L c.2.75 L d.3.00 L

27. Consider the reaction in which carbon disulfide (CS2) is burned in oxygen to produce carbon dioxide and sulfur dioxide (SO2) according to the balanced equation, CS2(l) + 3 O2(g) CO2(g) + 2 SO2(g) What is the least amount of CS2 needed to produce 10.00 g of SO2?

a. 2.971 g b.5.943 g c.11.89 g d.23.77 g

28. Consider the reaction in which carbon disulfide (CS2) is burned in oxygen to produce carbon dioxide and sulfur dioxide (SO2) according to the balanced equation, CS2(l) + 3 O2(g) CO2(g) + 2 SO2(g) How much CO2 will be produced along with 10.00 g of SO2?

a. 3.435 g b.6.870 g c.13.74 g d.27.48 g

29. Consider the reaction in which carbon disulfide (CS2) is burned in oxygen to produce carbon dioxide and sulfur dioxide (SO2) according to the balanced equation, CS2(l) + 3 O2(g) CO2(g) + 2 SO2(g) If 10.00 g of CS2 reacts as far as possible with 15.00 g of O2, how much SO2 will be produced?

a. 8.414 g b.16.83 g c.20.02 g d.30.03 g

30. In the presence of gaseous hydrogen sulfide (H2S) and oxygen, metallic silver is converted to silver sulfide (Ag2S) according to the balanced equation,

4 Ag(s) + 2 H2S(g) + O2(g) 2 Ag2S(s) + 2 H2O(l). If 38.2 g of Ag is allowed to react with 5.60 g of H2S and 3.00 g of O2, which reactant will be the limiting reagent?

a. Ag b.H2S c.O2 d.all of these

31. The gaseous elements H2 and O2 react explosively to form water (H2O). 3.00 L of H2 is mixed with 2.00 L of O2 and the mixture is ignited in a strong steel vessel. If the gas volumes are all measured at the same temperature and pressure, which gas remains unreacted, and what is its volume?

a. O2, 0.50 L b.O2, 1.00 L c.H2, 1.00 L d.H2, 2.00 L 32. After a chemical reaction was completed, the product was carefully weighed and the mass recorded. In order to calculate the percentage yield for the reaction, what additional information is required? a. the theoretical yield of the product b.the actual yield of the product c. the molar mass of the product d.all of these 33. A series of four sequential reactions is carried out during the synthesis of an organic compound. The



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percentage yields for the individual reactions are listed below. Reaction Number Percentage Yield 1 50% 2 19% 3 14% 4 16%

The overall yield for the synthesis is

a. 2.1105% b.16 % c.0.21 % d.0.0021% 34. Consider the production of acetylene gas (C2H2) by the reaction of calcium carbide (CaC2) with water as described in the balanced equation,CaC2(s) + 2 H2O(l) Ca(OH)2(s) + C2H2(g) This reaction can be assumed to go as far toward completion as possible. Also, all gas volumes refer to conditions of temperature and pressure where one mole of gas occupies 22.4 L. What volume of C2H2 will be produced by the complete reaction of 4.00 mol of CaC2?

a. 5.60 L b.22.4 L c.44.8 L d.89.6 L 35. Consider the production of acetylene gas (C2H2) by the reaction of calcium carbide (CaC2) with water as described in the balanced equation, CaC2(s) + 2 H2O(l) Ca(OH)2(s) + C2H2(g) This reaction can be assumed to go as far toward completion as possible. Also, all gas volumes refer to conditions of temperature and pressure where one mole of gas occupies 22.4 L. What mass of C2H2 will be produced by the complete reaction of 150.0 g of CaC2?

a. 2.34 g b.11.23 g c.30.42 g d.60.93 g 36. Consider the production of acetylene gas (C2H2) by the reaction of calcium carbide (CaC2) with water as described in the balanced equation,CaC2(s) + 2 H2O(l) Ca(OH)2(s) + C2H2(g) This reaction can be assumed to go as far toward completion as possible. Also, all gas volumes refer to conditions of temperature and pressure where one mole of gas occupies 22.4 L. What volume of C2H2 will be produced by the complete reaction of 28.5 g of CaC2 with 10.00 g of water?

a. 0.445 L b.0.555 L c.6.22 L d.9.97 L 37. Consider the production of acetylene gas (C2H2) by the reaction of calcium carbide (CaC2) with water as described in the balanced equation,CaC2(s) + 2 H2O(l) Ca(OH)2(s) + C2H2(g) This reaction can be assumed to go as far toward completion as possible. Also, all gas volumes refer to conditions of temperature and pressure where one mole of gas occupies 22.4 L. If 18.0 g of CaC2 reacts to produce 0.200 mol of C2H2, the percentage yield of the reaction is a. 36% b.58% c.80% d.90% 38. Consider the production of acetylene gas (C2H2) by the reaction of calcium carbide (CaC2) with water as described in the balanced equation,CaC2(s) + 2 H2O(l) Ca(OH)2(s) + C2H2(g) This reaction can be assumed to go as far toward completion as possible. Also, all gas volumes refer to conditions of temperature and pressure where one mole of gas occupies 22.4 L. If the percentage yield of C2H2 is known to be 80.0%, what volume of C2H2 is expected to be produced from 64.1 g of CaC2? a. 14.3 L b.17.9 L c.22.4 L d.28.0 L



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STP GAS AND MASS STOICHIOMETRY PROBLEMS 1. How many moles of nitrogen gas is needed to react with 44.8 liters of hydrogen gas to produce ammonia gas? 2. How many liters of ammonia are produced when 89.6 liters of hydrogen are used in the above reaction? 3. Ten grams of calcium carbonate was produced when carbon dioxide was added to lime water (calcium hydroxide in solution). What volume of carbon dioxide at STP was needed? 4. When 11.2 liters of hydrogen gas is made by adding zinc to sulfuric acid, what mass of zinc is needed? 5. What volume of ammonia at STP is needed to add to water to produce 11 moles of ammonia water? 6. How many grams of carbonic acid is produced when 55 liters of carbon dioxide is pressed into water? 7. magnesium hydroxide + ammonium sulfate magnesium sulfate + water + ammonia How much (grams) magnesium hydroxide do you need to use in the above reaction to produce 500 liters of ammonia? 8. How much strontium bromide is needed to add to chlorine gas to produce 75 liters of bromine? 9. What mass of ammonium chlorate is needed to decompose to give off 200 liters of oxygen? 10. Your car burns mostly octane, C8H18, as a fuel. How many liters of oxygen is needed to burn a kilogram of octane? 11. copper + sulfuric acid copper II sulfate + water + sulfur dioxide How many moles of copper are needed to produce 1000 L of SO2? 12. What volume of oxygen is needed to burn a pound of magnesium? 13. How many grams of sodium do you have to put into water to make 30 liters of hydrogen at STP? 14. ammonia gas and hydrogen chloride gas combine to make ammonium chloride. What volume of ammonia at STP is needed to react with 47.7 liters of hydrogen chloride at STP? 15. How many liters of oxygen are needed to burn 10 liters of acetylene?

ANSWERS TO GAS AND MASS STOICHIOMETRY PROBLEMS 1. 0.667 mol 2. 59.7 L 3. 2.24 L 4. 32.7 g

5. 246 L 6. 152 g 7. 651 g 8. 828 g

9. 604 g 10. 2.46 kL 11. 44.6 mol 12. 210 L

13. 61.6 g 14. 47.7 L 15. 25 L

PROBLEMS ON CONCENTRATION AND DENSITY 1. The lead brick on my desk measures 3 by 5 by 11 cm. Lead has a density of 11.34 g/cc. How many lead atoms are in that block? 2. The lab technician at the Planter's Peanut packing factory takes a bag of peanuts, puts water into it to dissolve the salt, and dilutes the solution to one liter. She then takes ten ml of that solution and titrates it against 0.132 M silver nitrate. One bag sample takes 31.5 ml of silver nitrate to endpoint. What mass of salt was in the bag? 3. What is the concentration of sugar (C12H22O11) if twenty grams are dissolved in enough water to make 2 liters? 4. Methyl alcohol (CH3OH) has a density of 0.793 kg/l. What volume of it is needed to add to water to make five liters of 0.25 M solution? 5. Magnesium has a density of 1.741 g/cc. What volume of Mg will burn in 20 liters of oxygen at 2.1 atm and 0°C? 6. Uranium metal can be purified from uranium hexafluoride by adding calcium metal. Calcium metal has a density of 1.54 g/cc. Uranium has a density of 18.7 g/cc. What mass of uranium do you get for a Kg of Ca? What volume of uranium do you get for a cubic meter of calcium? 7. What volume of 0.27 M sodium hydroxide is needed to react with 29.5 ml of 0.55 M phosphoric acid? 8. What volume of carbon dioxide is produced at 1 atm and 87 °C when 1.6 liters of methyl alcohol burns? What volume of liquid water is produced in this reaction? 9. Seven kilograms of mercury II oxide decomposes into mercury and oxygen. Mercury has a density of 13.6 g/cc/ What volume of mercury is produced? 10. Water and calcium oxide produce calcium hydroxide. How many grams of calcium hydroxide are made if you add 275 liters of water to enough calcium oxide? 11. Gasoline (C7H16) has a density of 0.685 kg/liter. How many liters of oxygen at 37 °C and 950 mmHg are needed to burn 15 liters of gasoline? 12. Sodium hydroxide and hydrochloric acid combine to make table salt and water. 14 mL of 0.1 M sodium hydroxide is added to an excess of acid. How many moles of table salt are made? How many grams of salt is that? 13. 50 mL of 0.25 M copper II sulfate evaporates to leave CuSO4·5H2O. (That is the pentahydrate crystal



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of copper II sulfate.) What is the mass of this beautiful blue crystal from the solution? 14. Chlorine gas is bubbled into 100 mL of 0.25 M potassium bromide solution. This produces potassium chloride and bromine gas. The bromine (which dissolves in water) is taken from the solution and measured at 27 °C and 825 mmHg. What is the volume of bromine? 15. 95.0 mL of 0.55 M sulfuric acid is put on an excess of zinc. This produces zinc sulfate and hydrogen. How many grams of zinc sulfate are made? 16. 27.6 mL of a 0.190 M solution of silver nitrate and 15.4 mL of an unknown (but excess) amount of sodium chloride combine to make a white precipitate silver chloride and some dissolved sodium nitrate. (a) How many moles of silver chloride are made? (b) How many grams of silver chloride is that? (c) How many moles of sodium nitrate are made? (d) What is the concentration of sodium nitrate in the final solution? 17. How many grams of potassium permanganate, KMnO4, is needed to make 1.72 liters of 0.29 M solution? 18. By my calculations, a drop of ethyl alcohol, C2H5OH , in an olympic-sized swimming pool produces a 1.20 E-10 M solution of alcohol in water. A drop is a twentieth of a mL. How many molecules of ethyl alcohol are in a drop of the water in the pool? 19. 93.0 mL of 0.150 M magnesium hydroxide is added to 57.0 mL of 0.4 M nitric acid. (Magnesium nitrate and water are formed. What is the concentration of the magnesium nitrate after the reaction?

ANSWERS TO PROBLEMS ON CONCENTRATION AND DENSITY 1. 5.44 E24 atoms 2. 24.3 g 3. 0.0292 M 4. 0.0504 L

5. 52.3 ml(cc) Mg 6a. 1.98 kg of U 6b. 1.63 E6 mL 7. 180 mL

8a. 1.17 kL CO2 8b. 1.43 L 9. 0.477 L 10. 1.13 E 6 g

11. 23.0 kL 12a. 1.4 E-3 mols 12b. 0.0819 g 13. 3.12 g

14. 284 mL 15. 8.44 g 16a. 5.24E-3 mol 16b. 0.752 g

16c. 5.24E-3 mols 16d. 122 mmolar 17. 78.8 mg 18. 3.61E9 molecules

19. 0.152 M

PROBLEMS USING COMPLETE ROADMAP 1. How many liters of ammonia at 0 °C and 25 atm. are produced when 10 g of hydrogen is combined with nitrogen? 2. How many milliliters of hydrogen at 0 deg C and 1400 mmHg are made if magnesium reacts with 15 mL of 6 M sulfuric acid? 3. How many atoms are in 25 liters of fluorine gas at 2.85 atm and 450 °C? 4. Liquid butane (C4H10 has a density of 0.60 g/cc. It burns to make carbon dioxide at 120 °C. What volume of carbon dioxide is produced at one atm when 350 liters of liquid butane burns? 5. Isopropyl alcohol, C3H7OH , makes a good fuel for cars. What volume of oxygen at 785 mmHg and 23 °C is needed to burn 8.54 E25 molecules of isopropyl alcohol? 6. How many moles of NaCl are in a liter of a 0.15 M NaCl solution? (0.15 M NaCl is physiological saline when sterilized.) 7. How many grams of NaCl must you put into a 50 liter container to make a physiological saline solution? 8. Chlorine gas is bubbled into 100 mL of 0.25 M potassium bromide solution. This produces potassium chloride and bromine gas. The bromine dissolves completely in the water. What is the concentration of bromine? 9. 95 mL of 0.55 M sulfuric acid is put on an excess of zinc. This produces zinc sulfate and hydrogen. How many grams of zinc sulfate are made? 10. Methyl alcohol (CH3OH) has a density of 0.793 Kg/L. What volume of it is needed to add to water to make twenty-five liters of 0.15 M solution? 11. Magnesium has a density of 1.741 g/cc. What volume of Mg will burn to produce a kilogram of magnesium oxide? 12. What volume of water vapor is produced at 716 mmHg and 87°C when 2.6 liters of methyl alcohol burns?

ANSWERS TO PROBLEMS USING COMPLETE ROADMAP 1. 2.99 L 2. 1.10 E3 mL 3. 1.45 E24 atoms 4. 4.67 E5 L

5. 1.50 E4 L 6. 0.15 moles 7. 439 g 8. 0.125 M

9. 8.44 g 10. 151 mL 11. 0.346 L 12. 1.29 E5 L



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Subjective Question Set 1. 1. Calculate the weight of 6.022 × 1023 molecules of CaCO3.

2. Calculate the weight of 12.044 × 1023 atoms of carbon.

3. What will be the number of oxygen atoms in 1 mole of O2

4. A piece of Cu weighs 0.635 g. How many atoms of Cu does it contain ?

5. Calculate the number of molecules in 11.2 litres of SO2 gas at NTP

6. One atom of an element × weighs 6.644 × 10�23g.Calculate the number of gram-toms in 40 kg of it.

7. From 200 mg of CO2, 1021 molecules are removed. How many moles of CO2 are left?

8. Calculate the volume of 20 g of hydrogen gas at NTP.

9. What volume shall be occupied by 6.022 × 1023 molecules of any gas at NTP ?

10. Calculate the number of atoms present in 5.6 litres of a (i) monoatomic, and (ii) diatomic gas at NTP.

11. Calculate the number of sulphate ions in 100 mL of 0.001 M H2SO4 solution

12. How many atoms are there in 100 amu of He ?

13. If a mole were to contain 1 × 1024 particles, what would be the mass of (i) one mole of oxygen, and (ii) a single oxygen molecule ?

14. The density of O2 at NTP is 1.429 g/L. Calculate standard molar volume of the gas.

15. The measured density of He at NTP is 0.1784 g/L. What is the weight of 1 mole of it?

16. A metal M of atomic weight 54.94 has a density of 7.42 g/cc. Calculate the apparent volume occupied by one atom of the metal.

17. Calculate the number of moles, and the number of atoms of H, S and O in 5 moles of H2SO4

18. Calculate the number of oxygen atoms and its weight in 50 g of CaCO3.

19. Calculate the number of atoms of each element present in 122.5 g of KClO3.

20. Calculate the total number of electrons present in 1.6 g of CH4

Ans Subjective Question Set 1. 1 2 3 4 5 100 grams

24 grams 2 × 6.022 × 1023

6.022 × 1021 3.011 × 1023

6 7 8 9 10 1000 1000 224

litres

6.022 × 1023 molecules are contained in 1 mole, and 1 mole, of any gas at NTP occupies a volume of 22.4 litres.

3.0 × 1023

11 12 13 14 15 6.022 × 1019

25 atoms 22.39 litres 4g

16 17 18 19 20 1.23 × 10�23 cc

H= 10 × 6.022 × 1023, S = 5 × 6.022 × 1023 , O = 20 × 6.022 × 1023

24 g No. of atoms of K = 1 × 6.022 × 1023 , Cl = 1 × 6.022 × 1023 , O = 3 × 6.022 × 1023

6.022 × 1023 molecules.



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Subjective Question Set 2. 1 Find the charge of 1 g-ion of N3� 2 Find the charge of 27 g of Al3+ ions in coulombs. 3 Equal masses of oxygen , hydrogen and methane are taken in a container in identical conditions. Find the ratio of the volumes of the gases 4 If the component of air are N2, 78%; O2, 21%; Ar, 0.9% and CO2, 0.1% by volume, what would be the moleculr weight of air ? 5 The atomic weights of two elements (A and B) are 20 and 40 respectively. If x g of A contains y atoms, how many atoms are present

6 Oxygen is present in a 1-litre flask at a pressure of 7.6 × 10�10 mm of Hg at 0°C. Calculate the number of oxygen molecules ink the flask?

7 The density of mercury is 13.6 g/cc. Calculate approximately the diameter of an atom of mercury, assuming that each atom is occupying a cube of edge length equal to the diameter of the mercury atom. 8 The density of a particular crystal of LiF is 2.65 g/cc. X-ray analysis shows that Li+ and F� ions are arranged in a cubic array at a spacing of 2.01 Å. From these data calculate the apparent Avogadro constant. [Li = 6.939, F = 18.998] (1Å = 10�8 cm) 9 To 50 mL of 0.5 M H2SO4, 75 mL of 0.25 M H2SO4 is added. What is the concentration of the final solution if its volume is 125 mL? 10 It is found that in 11.2 litres of any gaseous compound of phosphorus at NTP, there is never less than 15.5 g of P. Also, this volume of the vapour of phosphorus itself at NTP weighs 62 g. What should be the atomic weight and molecular weight of phosphorus ? 11 A polystyrene, having the formular Br3C6H3(C3H8)n, was prepared by heating styrene with tribromobenjoyl peroxide in the absence of air. If it was found to contain 10.46% bromide by weight, find the value of n. 12 It has been estimated that 93% of all atoms in the entire universe are hydrogen and that of the vast majority of those remaining are helium. Based on only these two elements, estimate the mass percentage composition of the universe. 13 The molecular weight of haemoglobin is about 65,000 g/mol. Haemoglobin contains 0.35% Fe by mass. How many iron atoms are there in a haemoglobin molecule? . 14 At room temperature the density of wter is 1.0 g/mL and the density of ethanol is 0.789 g/mL. What volume of ethanol contains the same number of molecules as are present in 175 mL of water ? 15 A sample of ethane has the same mass as 10.0 million molecules of methane. How many C2H6 molecules does the sample contain ? 16 How many grams of CaWO4 would contain the same mass of tungsten that is present in 569 g of FeWO4? (W = 184) 17 0.75 mole of solid 'A4' and 2 moles of gaseous O2 are heated in a sealed vessel, completely using up the reactants and producing only one compound. It is found that when the temperature is reduced to the initial temperature, the contents of the vessel exhibit a pressure equal to half the original pressure, What conclusions can be drawn from these data about the product of the reaction ?

Answer Subjective Question Set 2. 1 2 3 4 5 2.894 × 105

2.894 × 105 coulombs

O2 : H2 : CH4 = 1 : 16 : 2 1 Y

6 7 8 9 10 2.65 × 1010 2.9 × 10�8 cm 6.01 × 1023 0.35 M 0.35 M 11 12 13 14 15 n = 44.9 = 45 23.14% 4.06 moles of Fe V = 566.82 mL 2 n = 5.34

16 17 18 19 20 w = 539.05 g y = 4



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Subjective Question Set 3. 1. Find the number of atoms in 48 g of ozone at NTP. Ans. 1.8066 × 1024 2. What is the ratio of the volumes occupied by 1 mole of O2 and 1 mole of O3 in identical

conditions? Ans. 1 : 1 3. Calculate the mass of 5 moles of CaCO3 in grams ? Ans. 500 (g) 4. The vapour density of a gas is 11.2.Calculate the volume occupied by 11.2 g of the gas at

NTP. Ans. 11.2 litres 5. Calculate the number of oxygen atoms in 0.2 mole of Na2CO3.10H2O. Ans. (1.56 × 1024) 6. Calculate the number of moles of CuSO4 contained in 100 mL of 1 M CuSO4 solution. Also find the

number of 24SO ions in it Ans. 0.1 mole, 0.6022 × 1023

7. Find the total number of nucleous present in 12 g of 12C atoms. Ans. (12 × 6.022 × 1023) 8. Find (i) the total number of neutrons, and (ii) the total mass of neutrons in 7 mg of 14C. (Assume that

the mass of a neutron = mass of a hydrogen atom) ANS. 24.088 × 1020, 0.004 g 9. How many moles are there in 1 metre3 of any gas at NTP ? (1m3 = 103 litres)Ans. 44.6 moles 10. 3g of a salt of molecular weight 30 is dissolved in 250 g of water. Calculate the molality of the

solution. Ans. (0.4 m) 11. Calculate the volume occupied by 5.25 g of nitrogen at 26°C and 74.2 cm of pressure

Ans. 4.71 litre 12. Find the ratio of the number of molecules contained in 1g of NH3and 1 g of N2.Ans. 28 : 17 13. How many molecules in 1 kg of H2 and 1 kg of O2 the same ? What is the ratio of weights of H2

and O2, the mixture of which contains equal number of molecules of each gas?Ans. (8.06 × 1018) 14. Is the number of molecules in 1 kg of H2 and 1 kg of O2 the same ? What is the ratio of weights of

H2 and O2, the mixture of which contains equal number of molecules of each gas ? Ans.No, (1 : 16) 15. The measured density at NTP of a gaseous sample of a compound was found to be 1.78g/L.

What is the weight of 1 mole of the gaseous sample ? ANS. 39.9g 16. If the concentration of a solution is 2M calculate the number of millimoles present in 2 litres of the

solution. Ans. 4000 17. How many moles of oxygen are contained in one litre of air if its volume content is 21% at NTP

Ans. 0.0093 18. How many atoms do mercury vapour molecules consist of it the density of mercury vapour

relative to air is 6.92 ? (Hg=200). The average mass of air is 29 g/mole Ans. One 19. Calculate the total number of atoms in 0.5 mole of K2Cr2O7. Ans. 3.31 × 1024 20. What is the volume of 6g of hydrogen at 1 atm and 0°C ? Ans. 67.2 litres 21. What is the density of oxygen gas at NTP ? Ans. 1.429 g/L 22. Calculate the total number of electrons present in 18 mL of water.Ans. (10 × 6.022 × 1023) 23. Calculate the number of electrons, protons and neutrons in 1 mole of 16O�2 ions .

Ans. 10 × 6.022 × 1023,, 8 × 6.022 × 1023 24. Find the mass of nitrogen contained in 1 kg of (i) KNO3, (ii) NH4NO3, and (iii) (NH4)2HPO4.

Ans. (i) 138.5g (ii) 350 g and (iii) 212 g 25. Find the mass of each element in 7.84g of FeSO4.(NH4)2SO4. 6H2O. What will be the volume of

O2 at NTP in this sample ? Ans. (3.136 litre) 26. The density of solid AgCl is 5.56 g/cc. The solid is made up of cubic array of alternate Ag+ and

Cl� ions at a spacing of 2.773 Å between centres. From these data calculate the Avogadro constant. Ans. 6.04 × 1023

27. Three atoms of magnesium combine with 2 toms of nitrogen. What will be the weight of magnesium which combines with 1.86 g of nitrogen ? Ans4.86 (g)

28. 600 mL of a mixture of O3 and O2 weighs 1 g of NTP. Calculate the volume of ozone in the mixture. Ans. 200 mL

29. The vapour desnity (hydrogen = 1) of a mixture consisting of NO2 and N2O4 is 38.3 at 26.3 C. Calculate the number of moles of NO2 in 100 g of the mixture. Ans. 0.437 mole

30. A nugget of gold and quartz weighs 100g. Sp.gr. of gold, quartz and the nugget are 19.3, 2.6 and 6.4 respectively. Calculate the weight of gold in the nugget. Ans. 68.6 g

31. The neucleus of an atom of x is supposed to be a sphere with a radius of 5 × 10�13 cm. Find the density of the matter in the atomic nucleus if tha tomic weight of x is 19. Ans. 6.02 × 1013g/mL



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32. Copper forms two oxides. For the same amount of copper, twice as much oxygen was usedj to form the first oxide than to form the second one. What is the ratio of the valencies of copper in the first and second oxides ? Ans. 2 : 1

33. 105 mL of pure water (4°C) is saturated with NH3 gas, producing a solution of density 0.9 g/mL. If this solution contains 30% of NH3 by weight, calculate its volume. Ans. 166.67 mL

34. How many iron atoms re present in a stainles steel ball bearing a radius of 0.1 inch (1 inch = 2.54 cm) ? The stainless steel contains 85.6% Fe by weight and has a density of 7.75 g/cc. Ans. 4.91 × 1021

35. How many litres of liquid CCl4(d = 1.5 g/cc.) msut be measured out to contain 1 × 1025 CCl4 molecules Ans. 1.61 L.

36. A sample of potato starch was ground in a ball mill to give a strchlike molecule of lower molecular weight. The product analysed 0.086% phosphorus. If each molecule is assumed to contain one atom of phosphorus, what is the molecular weight of the material ? Ans. 3.6 × 104 amu

37. The dot at the end of this sentence has a mass of about one microgram. Asuming that the black stuff iscarbon, calculate the approximate number of atoms of carbon needed to make such a dot. (1 microgram = 1 × 10�6 g) Ans. 5 × 1016 atmos

38. To what volume must 50 mL of 3.50 M H2SO4 be diluted in order to make 2M H2SO4 ? Ans. 87.5 mL

39. Sulphur molecules exist under varous conditions as S8, S6, S4, S2 and S. (a) Is the mass of one mole of each of these molecules the same (b) Is the number of molecules in one mole of each of these molecules the same ? (c) Is the mass of sulphur in one mole of each of these molecules the same. (d) Is the number of atoms of sulphur in one mole of each of these molecules the same? Ans. (NO, Yes, NO, NO)

40. Two minerals that contain Cu are CuFeS2 and Cu2S. What mass of Cu2S would contain the same mass of Cu as is contained in 125 lb of CuFeS2 ? Ans. 54.2 lb

41. What is the maximum number of moles of CO2 that couldbe obtained from the carbon in 4 moles of Ru2(CO3)3? Ans. 12 mol

42. What mass of NaCl would contain the same total number of ions as 245 g of MgCl2? Ans. 225 g

43. An unknown sample weighing 1.5 g was found to contain only Mn and S. The sample was completelyreacted with oxygen and it produced 1.22 g of Mn(II) oxide and 1.38 g of SO3 What is the simplest formula for this compound ?. Ans. MnS

44. The two sources of Zn, that is, ZnSO4 and Zn(CH3COO)2 . 2H2O, can be purchased at the same price per kilogram of compound. Which is the most economical source of kZn and by how much? Ans. (ZnSO4), 35.9%

45. How many moles of H2O form when 25.0 mL of 0.10 M HNO3 solution is completely neutralised by NaOH? Ans. 2.5 × 10�3

46. Which would be larger: an atomic mass unit based on the current standrard or one based on the mass of a Be-9 atom set at exactly 9 amu ? Ans. latter

47. The enzyme caronic hydraze catalyses the hydration of CO2. This reaction : CO2 + H2O H2COy is involved in transfer of CO2 from tissues to the lungs via the bloodstram. KOne enzyme molecule hydrates 106 molecules of CO2 per second. How many kg of CO2 are hydrated in one hour in one litre by 1 × 10�6M enzyme ? Ans. 0.1584 kg

48. An oxybromo compound, KBrxO3, where x is unknown, is analysed and found to contain 52.92% Br. What is the value of x ? Ans. 2

49. Radius disintegrates at an average rate of 2.24 × 1013 -particles per minute. Each -particle takes up two electrons from the air nd becomes a neutral helium atom. After 420 days, helium gas collected was 0.5 mL, measured at 27°C and 750 mmHg. Calculate the Avogadro constant. Ans. 6.7 × 102



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Subjective Question Set 4. 1 What amount of CaO will be produced by 1 g of calcium ? Ans. 1.4 g 2 What weight of oxygen willr eact with 1 g of calcium ? (Ca = 40) Ans. 0.4 g 3 (a) Calculate the volume occpuied by 1 mole of He, H and O atoms at N

(b) What volume of oxygen (NTP) will be required to react with 1 g of Ca? ans.(a) 11.2 litre (b) 0.28 litre

4 A sample of KClO3 an decomposition yielded 448 m of oxygen gas at NTP. Calculate (i) weight of oxygen produced, (ii) weight of KClO3 originally taken, and (iii) weight of KCl produced. (K = 39, , Cl = 35.5 and O = 16) ans(i) 0.02 × 32 = 0.64, (ii) 1.634 , (iii) 0.9937 g.

5 27.6 g of K2CO3 was treated by aseries of reagents so as to convert all of its carbon to K2 Zn3[Fe(CN)6]2. Calculate the weight of the product. Ans. 11.6 g

6 In a gravimetric determination of P, an aqueous solution of dihydrogen phsosphate ion H2PO4� is

treated with a mixture of ammonium and magnesium ions to precipitte magnesium ammonium phosphate, Mg(NH4)PO4.6H2O. This is heated and decomposed to magnesium pyrophosphate, Mg2P2O7, which is weighed. A solution of H2PO4

� yielded 1.054 g of Mg2P2O7. What weight of NaH2PO4 was present originally ? (Na = 23, H = 1, P = 31, O = 16, Mg = 24) Ans. 1.14 g.

7 What weight of AgCl will be precipitated when a solution containing 4.77 g of NaCl is added to a solution of 5.77 g of AgNO3 ? (Na = 23, Cl = 35.5, Ag = 108, N = 14 and O = 16) Ans. 4.87 g

8 What is the number of moles of Fe(OH)3(s) that can be produced by allowing 1 mole of Fe2S3, 2 moles of H2O and 3 moles of O2 to react ? Ans. 1.34

9 Equal weights of phosphorus and oxygen are heated in a closed vessel producing P2O3 and P2O5 in a 1 : 1 mole ratio. If the limiting component is exhausted , find which component and also what fraction of it is left over. ans.3.125%

10 In a process for producing acetic acid, oxygen gas is bubbled into acetaldehyde containing managanese (II) acetate (catalyst) under pressure at 60°C. 2CH3CHO + O2 2CH3COOH In a laboratory test of this reaction, 20 g of CH3CHO and 10 g of O2 were put into a reaction vessel. (a) How many grams of CH3COOH can be produced ? (b) How many grams of the excess reactant remain after the reaction is complete ? Ans. (a) 27.27 g (b) 2.73 g

11 0.75 mole of solid 'A4' and 2 moles of gaseous O2 are heated in a sealed vessel, completely using up the reactants and producing onlyj one compound. It is found that when the temperature is reduced to the initial temperature, the contents of the vessel exhibit a pressure equal to half the original pressure. What conclusions can be drawn from these data about the product of the reaction ? Ans. 3A4 + 8O2 4A3O4

12 Calculate the weight of time (CaO) that can be prepared by heating 200 kg of limestone (CaCO3) which is 95% pure. Ans. 106.4 kg.

13 g-atom of Ca was burnt in excess of oxygen and the oxide was dissolved in water to make up a one litre solution. Calculate the normality of the alkaline solution. Ans. 2N.

14 10 cc of H2O2 solution when reacted with Ki solution produced 0.5 g of iodine. Calculate the percentage purity of H2O2. (I = 127) Ans. 0.669%

15 0.32 mole of LiAlH4 in ether solution was placed in a flask and 74 g (1mole) of t-butyl alcohol was added. The product LiAlHC12H27O3 weighed 81.28 g. Is the claim that the yield is 'quantitative' a valid one if Li atoms are conserved ? (Li = 7m, Al = 27, H = 1, C = 12, O = 16) Ans. yield is 100%

16 52.5 millimoles of LiAlH4 was treated with 15.6 g (210 millimiles) of t-butyl alcohol. A total of 157.5 millimoles of hydrogen was evolved for the reaction. LiAlH4 + 3(CH3)3COH H2 + Li(CH3)3O]3[CH3O]Al The addition of an excess of another alcohol, methanol, to the above reaction mixture caused the fourth H atom of the LiAlH4 to be replaced according to the equation. Li(CH3)3O]3 AlH + CH3OH H2 + Li[(CH3)3O]3[CH3O] Al How much H2 was evolved due to the addition of CH3OH ? Ans. 52.5 millimoles of H2 .

17 Equal weights of Zn metal and iodine are mixed together and the iodine is completely converted to ZnI2. What fraction by weight of the original zinc remains unreacted? (Zn = 65, I = 127) Ans. 0.74.

18 1.0 g of an alloy of Al and Mg when treated with excess of dil. HCl forms MgCl2, AlCl3 and hydrogen. Collected over Hg at 0°C, has a volume of 1.20 litres at 0.92 atm pressure. Calculate the composition of the alloy. (al = 27 and Mg = 24). Ans. 45%



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19 A 1g mixture of cuprous oxide and cupric oxide was quantitavely reduced to 0.839 g of metallic copper. What was the weight of cupric oxide in the original sample ? (Cu = 63.5, O = 16) Ans. 0.55g

20 A mixture of FeO and Fe3O4 when heated in air to a constant weight, gains 5% jin weight. Find the composition of the initial mixture. Ans. % of FeO = 20.02% and % of Fe3O4 = 79.88%

21 What weight of CO is required to form Re2(CO)10 from 2.50 g of Re2O7 according to the unbalanced reaction : Re2O7 + CO Re2(CO)10 + CO2 (Re = 186.2, C = 12 and O = 16 Ans. 2.46 g

22 1-g sample of KClO3 was heated under such conditions that a part of it decomposed according to the eqaution : (i) 2KClO3 = 2KCl + 3O2 and the remaining underwent change according to the equation (ii) 4KClO3 = 3KClO4 + KCl If the amount of O2 evolved was 146.8 mL at NTP, calculate the percentage by weight of KClO4 in the residue. Ans. 49.85%

23 A mixture of KBr and NaBr weighing 0.560 g was treated with aqueous Ag+ and all the bromide ion was recovered as 0.97g of pure AgBr. What was the fraction by weight of KBr in the sample ? (K = 39, Br = 80, Ag = 108, Na = 23) Ans. 0.2378 g

24 Igniting MnO2 in air converts it dquantitatively to Mn3O4. a sample of pyrolusite is of the following composition : MnO2 � 80%, SiO2 and other consituents �15%, rest being water. Thesample isignited in air to constant (Mn = 55, O = 16) Ans. 59.37%

25 1.84 g of a mixture of CaCO3 and MgCO3 was heated to a constant weight. The constant weight of the residue was found to be 0.96 g. Calculate the percentage composition of the mixture. (Ca = 40, Mg =24, C = 12, O =16) Ans. 45.66%

26 A sample of mixture of CaCl2 and NaCl weighing 4.22 g was treated to precipitate all the Ca as CaCO3, which was then heated and quantitatively converted to 0.959 g of CaO. Calculate the percentage of CaCl2 in the mixture. (Ca = 40, O = 16, C = 12 and Cl = 35.5)Ans. 45.04%

27 A 2-g sample containing Na2CO3 and NaHCO3 loses 0.248 g when heated to 300°C, the temperature at which NaHCO3 decomposes to Na2CO3, CO2 and H2O. What is the percentage of Na2CO3 in the given mixture? (Na = 23, C = 12, O = 16 and H = 1) Ans.66.4%

28 A solution of lead nitrate prepared by dissolving 2.07 g of pure lead in nitric acid was treated with HCl, Cl2 gas and NH4Cl. What will be the maximum weight of (NH4)2 PbCl6 so produced ? (N = 14, H = 1, Pb = 207, Cl = 35.5) Ans. 50%

29 Three different brands of 'liquid chlorine' are available in the market for use in purifying water of swimming pools. All are sold at the same rate of Rs. 10 per litre and all are water solutions. Brand A contains 10% hypochlorite (ClO) (wt./vol.), brand B contains 7% available chlorine (Cl) and brand C contains 14% sodium hypochlorite (NaClO). Which of the three would you buy ? Ans. 6.67 g

30 In the analysis of a 0.50 g sample of feldspar, a mixture of the chlorides of Na and K is obtained, which weighs 0.1180g. Subsequent treatement of the mixed chlorides with silver nitrate gives 0.2451 g of AgCl. What is the percentage of sodium oxide and potassium oxide in feldspar ? Ans. Na2O =3.6% , K2O = 10.6%

31 4.08 g of a mixture of BaO and an unknown carbonate MCO3 was heated strongly. Theresidue weighed 3.64g. This was dissolved in 100 mL of 1.0 N HCl. The excess acid required 16 mL of 2.5N NaOH solution for complete neutralisation. Identify the metal M.

32 A mixture contains NaCl and an unknown chloride MCl. (i) 1g of this is dissolved in water. Excess of acidified AgNO3 solution is added to it. 2.567 g of a white precipitate is formed. (ii) 1.0 g of the original mixture is heated to 300°C. some vapours come out which are absorbed in acidified AgNO3 solution. 1.341 g of a white precipitate is obtained. Find the molecular weight of the unknown chloride. Ans. 53.5

33 A solid mixture (5g) consisting of lead nitrate and sodium nitrate was heated below 600°C until the weight jof the residue is constant. If the loss in weight is 28%, find the amount of the lead nitrate and sodium nitrate in the mixture. Ans. 1.6754 g.

34 In a particular experiment, 272 g of phosphorus, P4, reacted with excess of oxygen to form P4O10 in 89.5% yield. In the second step of the reaction, a 97.8% yield of H3PO4 was obtained. What mass of H3PO4 was obtained. Ans. 752.65 g

35 For the production of equal amounts of hydrogen from the following reactions, which metal, Zn or Al, is less expensive if Zn costs about half as much as Al on a mass basis and by how much? Zn + 2HCl ZnCl2 + H2 2Al + 6HCl 2AlCl3 + 3H2 Ans. 44.61%

36 20.2 mL of CH3COOH reacts with 20.1 mL of C2H5OH to form CH3COOC2H5 (d = 0.902 g/mL) by the following reaction



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CH3COOH + C2H5OH CH3COOC2H5 + H2O (a) Which compound is the limiting reagent ? (b) If 27.5 mL of pure ethyl acetate is produced, what is the percent yield ? Densities of CH3COOH and C2H5OH are 1.05 g/mL and 0.789 g/mL respectively.

37 A mixture of pure AgCl and pure AgBr is found to contain 60.94% Ag by mass. What are mass percentages of Cl and Br in the mixture ? (Ag = 108, Cl = 35.5, Br = 80) Ans. Cl = 4.85%, Br = 34.19%

38 From the following reaction sequence, CaC2 + H2O CaO + C2H2 C2H2 + H2 C2H4

nC2H4 (C2H4)n Calculate the mass of polyetheylene which can be produced from 10 kg of CaC2 Ans. 4375g 39 From the following series of reactions,Cl2 + 2KOH KCl + KClO + H2O

3KClO 2KCl + KClO3 4KClO3 3KClO4 + KCl

Calculate the mass of chlorine needed to produce 100 g of KClO4. Ans. 204.5 g

Subjective Question Set 5. 1. Calculate orally (i) How many moles of CaCO3 shall be produced from 5 moles of Ca atoms? (ii) How many moles of BaSO4 shall be formed from 5 moles of BaCl2 ? (iii) How many moles of Na2O shall be produced from 5 moles of Na atoms ? Ans. (i) 5 (ii) 5 (iii) 2.5 2. What weight of oxygen will react with 40 g of Ca ? Ans.16 g 3. Calculate, without balancing the following equation, the volume of chlorine at NTP produced from 50 g of sodium chloride. NaCl + MnO2 + H2SO4 NaHSO4 + MnSO4 + Cl2 + H2O Ans. (9.575 litres) 4. Two tonnes of an iron ore containing 94% of Fe2O3 produced iron in pure stte. Calculate the weight of iron. Ans. 1315 Kg. 5. Calculate the volume of acetylene at NTP produced byj 100 g of CaC2 with water. Ans. 35 litres 6. How many litres of destonating gas will be produced at NTP in thedecomposition of 0.1 mole of water by anelectric current ? Ans. 3.36 litres 7. Find the mass ofj Cu(NO3)2.3H2O produced by dissolving 10 g of copper in nitric acid and then evaporating the solution. Ans. 38 g 8. 4.90 g of KClO3, jon heating shows a weight loss of 0.384 g. What percent of the original KClO3 was decomposed ? ans. 20% 9. When the mixture of MgCO3 and CaCO3 was heated for a long time. Theweight decreased by 50%. Calculate the percentage composition of the mixture. Ans.MgCO3:7159%; CaCO3 : 28.41% 9. How many moles of Zn(FeS2)2 can can be made from 2 g of zn, 3g of Fe and 4 g of S ? Ans. 0.0269 mole 10. Calculate the weight of V2O5 produced from 2g of VO and 5.75 g of Fe2O3. VO + Fe2O3 FeO + V2O5 Ans. (2.18g) 11. Equal weights of mercury and iodine are allowed to react completely to form a mixture of mercurous and mercuric iodide leaving one of the reactants. Calculate the ratio by weight of Hg2I2 and HgI2 formed. Ans. 0.532 : 1 12. 5.5 g of a mixture of FeSO4.7H2O and Fe2(SO4)3.9H2O requires 5.4 mL of 0.1 N KmnO4 solution for complete oxidation. Clculate the number of moles of hydrated ferric sulphate in the mixture. Ans. (0.0095 mole) 13. Anhydrous sodium sulphate can absorb water vapour and be converted to the decahydrate. By how many grams fwould the mass of a 1-g sample of the thoroughly dried Na2SO4 increase if exposed to sufficient water vapour to be converted to the decahydrate ? Ans. (1.27 g) 14. A partially dried clay sample contained 50% of sillica and 7% of water. The original clay contained 12% of water. Find the percentage of silica in the original sample. Ans. 47.3% 15. 1g of a sample containing NaCl, NaBr and an inert material, with excess of AgNO3, produces 0.526 g of precipitate of AgCl and AgBr. By heating his precipitate in a current of chlorine. AgBr converted to AgCl and the precipitate then weighed 0.426 g. Find the percentage of NaCl and NaBr in the sample. ans. NaCl : 4.25%, NaBr : 23.2% 16. 3.90 g of a mixture ofk Al and Al2O3, when reacted with a solution of sodium hydroxide, produced 840 mL of a gas at NTP. Find the composition of the mixture. Ans. (Al : 17.3%)



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17. To detemine the content in commercial NaOH, 2g of the latter was dissolved in water and an excess amount of ank AgNO3 solution ws added to this solution. The precipitate formed was washed and dried. Its mass was 0.287 g. Find the mass of NaCl in the initial sample. Ans. (0.117 g) 18. One litre of an acidified solution of KMnO4 containing 15.8 g of KMnO4 is decolourised by passing sufficient amount of SO2. If SO2 is produced by roasting iof iron pyrites (FeS2). What will be the amount of pyrites required to produce the necessary amount of SO2 ? Ans.(15 g) 19. When a mixture of NaBr and NaCl is repeatedly digested with sulphuric acid, all the halogens are expelled and Na2SO4 is formed quantitatively. With a particular mixture, it was found that the weight of Na2SO4 obtained was precisely the same as the weight of NaBr-NaCl mixture taken. Calculate the ratio of the weights of NaCl and NaBr in the mixture Ans. 1.454 : 1 20. 25.4 g of iodine and 14.2 g of chlorine are made to react completely to yield a mixture jof ICl and ICl3 Calculate the number of moles of ICl and ICl3 formed. Ans. 0.1 mole, 0.1 mole 21. An alloy of aluminium and copper was treated with aqueous HCl. The aluminium dissolved according to the reaction :

Al + 3H+ Al3+ +

32 2H

but the copper remained a pure metal. A 0.350 g smaple of the alloy gave 415 cc of H2 measured at 273 K and 1 atm pressure. What is the weight percentage of Al in the alloy ? Ans. 95.3% 22. 1g of dry green algae absorbs 4.7×10�3mole of CO2 per hour by photosynthesis.If the fixed carbon atoms were all stored after photosynthesis as starch, (C6H10O5)n, how long would it take for the algae to double their own weight assuming photosynthesis takes at a constant rate ? Ans. 7.88 hours 23. Crude calcium carbide is made in jan electric furnace by the following reaction : CaO + 3C CaC2 + CO The product contains 85% of CaC2 and 15% of unreacted CaO. (a) How much CaO is to be added to the furnace charge for each 1000 kg of CaC2 (pure) produced? (b) How much CaO is to be added to the furnace charge for each 1000 kg of crude product ? Ans.(a) 1041.5 kg ; (b) 893.7 kg 24. 2.5 g of a mixture of BaO and CaO when treated with an excess of H2SO4 , produced 4.713 g of the mixed sulphates. Find the percentage of BaO present in the mixture. Ans.50% 25. A mixture of NaI and NaCl, when heated with H2SO4, produced the same weight of sodium sulphate as that of the original mixture. Calculate percentage of NaI in the mixture. Ans. 28.85% 26. 7.46 g of KCl was heated with excess of MnO2 and H2SO4. The gas so produced was then passed through a solution of KI. Calculate the weight of iodine. Ans. 12.7 g 27. Carnalite is a double chloride of potassium and magnesium containing 38.86% of water. 0.458 g of it gave 0.71 g of AgCl and 0.666 g of it gave 0.27 g Mg2P2O7. Find the percentage of KCl in the carnalite. Ans. 26.46% 28. What volume of hydrogen at NTP is needed to reduce 125 g of MoO3 to the metal ? Ans. 58.3 litres 29. How much gas (in litres) will be produced at 0°C and 760 mm of pressure when 10 g of oxalic acid was heated with concentrated sulphuric acid ? ans. 4.97 litres 30. A natural gas sample contains 84% (by volume) of CH4, 10% of of C2H6 , 3% of C3H8 and 3% of N2. If a series of catalytic reactions could be used for converting all the carbon atoms of the gas into butadiene, C4H6, with 100% efficiency, how much butadiene could be prepared from 100 g of the natural gas ? Ans. 82 g 31. What weights of P4O6 and P4O10 will be produced by the combustion of 2g of P4 in 2g of oxygen leaving no P4 and O2 Ans. 1.996 g, 2.004 32. From the following reactions, 2CoF2 + F2 2CoF3 (CH2)n + 4n CoF3 (CF2)n + 2nHF + 4n CoF2 calculate how much F2 will be consumed to produce 1 kg of (CF2)n. Ans. 1.52 kg 33. A mixture containing KClO3, KHCO3, K2CO3 and KCl was heated, producing CO2, O2 and H2O gases according to the following equations : 2KClO3(s) 2KCl(s) + 3O2 2KHCO3(s) K2O(s) + H2O(g) + 2CO2(g) K2CO3(s) K2O(s) + CO2(g) The KCl does not react under the conditions of the reaction. If 100.0 g of the mixture produces 1.80 g of H2O, 13.20 g of CO2 and 4.0 g of O2,what was the composition of the original mixture ? Ans. (KClO3 : 10.2 g, KHCO3 : 20g, K2CO3 : 13.8 g



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Chemistry: Molarity and Stoichiometry 1. Calcium hydroxide (�slaked lime�) and sulfuric acid react to produce calcium sulfate and water according to the following balanced equation: Ca(OH)2(aq) + H2SO4(aq) CaSO4(s) + 2 H2O(l) a. How many liters of 0.5 M calcium hydroxide do you need in order to have 5.5 moles of calcium hydroxide? b. Find the number of moles of sulfuric acid needed to react with 5.5 moles of calcium hydroxide. c. If the sulfuric acid has a concentration of 0.82 M, how many liters of it are needed to react with 5.5 moles of calcium hydroxide? 2. Calcium carbonate (�limestone�) reacts with hydrochloric acid according to the following balanced equation: CaCO3(aq) + 2 HCl(aq) CO2(g) + CaCl2(aq) + H2O(l) a. What mass of calcium carbonate is needed to make 1.2 liters of a 1.7 M calcium carbonate solution? b. What volume of 3.0 M hydrochloric acid is needed to completely react with the amount of calcium carbonate in Part 2a above? c. Based on Parts 2a and 2b above, how many moles of water would be produced? 3. Ammonium chloride and calcium hydroxide react according to the following balanced equation: 2 NH4Cl(aq) + Ca(OH)2(aq) CaCl2(aq) + 2 NH3(g) + 2 H2O(l) a. What mass of ammonium chloride is needed to make 1.0 liter of a 2.0 M ammonium chloride solution? b. What mass of calcium hydroxide is needed to make 2.0 liters of a 2.0 M calcium hydroxide solution? c. How many grams of calcium chloride will be made when 1.0 liter of a 1.0 M calcium hydroxide solution react with excess ammonium chloride? 4. Zinc and hydrochloric acid react according to the following balanced equation: Zn(s) + 2 HCl(aq) ZnCl2(aq) + H2(g) a. What volume of 0.1 M hydrochloric acid will react with 26 grams of zinc? b. What mass of zinc will react with 2.0 liters of 0.25 M hydrochloric acid? c. How many liters of hydrogen will you make (at STP) if you react 2.74 L of 0.45 M hydrochloric acid with excess zinc? Answers: 1a. 11.0 L of 0.5 M Ca(OH)2(aq) 3a. 107 g NH4Cl 1b. 5.5 mol H2SO4 3b. 296 g Ca(OH)2 1c. 6.71 L of 0.82 M H2SO4(aq) 3c. 111 g CaCl2 2a. 204 g CaCO3 4a. 7.95 L of 0.1 M HCl(aq) 2b. 1.36 L of 3.0 M HCl(aq) 4b. 16.4 g Zn 2c. 2.04 mol H2O 4c. 13.8 L H2 (at STP)

Chemistry: Stoichiometry � Problem Sheet 1 1. Silver and nitric acid react according to the following balanced equation: 3 Ag(s) + 4 HNO3(aq) 3 AgNO3(aq) + 2 H2O(l) + NO(g) A. How many moles of silver are needed to react with 40 moles of nitric acid? B. From the amount of nitric acid given in Part A, how many moles of silver nitrate will be produced? C. From the amount of nitric acid given in Part A, how many moles of water will be produced? D. From the amount of nitric acid given in Part A, how many moles of nitrogen monoxide will be made? 2. Given the balanced equation: 2 N2H4(l) + N2O4(l) 3 N2(g) + 4 H2O(g) A. How many moles of dinitrogen tetrahydride are required to produce 57 moles of nitrogen? B. How many moles of dinitrogen tetroxide are required to produce 57 moles of nitrogen? C. How many moles of water are produced when 57 moles of nitrogen are made? 3. Calculate the mass of aluminum oxide produced when 3.75 moles of aluminum burn in oxygen. Answers: 1A. 30 mol Ag 1C. 20 mol H2O 2A. 38 mol N2H4 2C. 76 mol H2O 1B. 30 mol AgNO3 1D. 10 mol NO 2B. 19 mol N2O4 3. 191 g Al2O3 4. At a very high temperature, manganese is isolated from its ore, manganomanganic oxide, via the following balanced equation: 3 Mn3O4(s) + 8 Al(s) 4 Al2O3(s) + 9 Mn(s) A. How many manganese atoms are liberated if 54.8 moles of Mn3O4 react with excess aluminum.



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B. How many moles of aluminum oxide are made if 3580 g of manganomanganic oxide are consumed? C. How many moles of manganomanganic oxide will react with 5.33 x 1025 atoms of aluminum? D. If 4.37 moles of aluminum are consumed, how many molecules of aluminum oxide are produced? 5. Camels store the fat tristearin (C57H110O6) in the hump. Besides being a source of energy, the fat is a source of water for the camel because when the fat is burned, the following reaction occurs: 2 C57H110O6(s) + 163 O2(g) 114 CO2(g) + 110 H2O(l) A. At STP, what volume of oxygen is required to consume 0.64 moles of tristearin? B. At STP, what volume of carbon dioxide is produced in Part A? C. If 22.4 L of oxygen is consumed at STP, how many moles of water are produced? D. Find the mass of tristearin required to produce 55.56 moles of water (about 1 liter of liquid water). Answers: 4A. 9.9 x 1025 atoms Mn 4C. 33.2 mol Mn3O4 5A. 1168 L O2 5C. 0.675 mol H2O 4B. 20.9 mol Al2O3 4D. 1.3 x 1024 m�cules Al2O3 5B. 817 L CO2 5D. 899 g C57H110O6

Stoichiometry 1. Ammonia (NH3) may be produced by the reaction of nitrogen and hydrogen according to the balanced equation: N2 + 3 H2 → 2 NH3 a. If 23.2 grams of nitrogen react, how many grams of NH3 are produced? b. If 23.2 grams of nitrogen react, how much hydrogen also reacts? 2. Nitroglycerin, C3H5(NO3)3 decomposes forming N2, O2, CO2 and H2O according to the balanced reaction: 4 C3H5(NO3)3 → 6 N2 + O2 + 12 CO2 + 10 H2O a. How many grams of nitroglycerin are needed to produce 1 kilogram of CO2? b. If 100.0 grams of nitroglycerin are reacted, what volume of liquid water will be found? (HINT: Density of liquid water is 1.0 g/ml) 3. Sodium and oxygen react in a direct combination reaction to produce sodium oxide. a. Write a balanced equation for this reaction. b. If 155 grams of sodium react, how much oxygen (in grams) is needed? c. If 557 grams of oxygen react with excess sodium, how many grams of sodium oxide will form? 4. Some copper is produced by reaction of CuSO4 with zinc metal. a. Write the balanced equation. b. In order to recover all the copper, how much zinc should be used if there are 63.5 grams of copper sulfate in the solution? c. How much copper can be recovered in part (b)? d. If the experiment began with 28.7 grams of copper, what is the percentage of the copper recovered? 5. When sodium hydroxide and sulfuric acid, H2SO4, react together, a neutralization reaction occurs. a. Write the balanced equation. b. If 0.80 moles of sulfuric acid react, how much NaOH is needed? c. If 0.80 moles of sulfuric acid react, how many grams of each product will form? 6. Balance the following: NO2 + H2O HNO3 + NO a. How many moles of NO are produced from 13.8 grams of NO2? b. How many grams of NO are produced form 13.8 grams of NO2? 7. When iron is heated in air (oxygen), Fe2O3 is created. If 1.50 grams of Fe are heated, what will be the weight of Fe2O3 created? 8. You wish to make Ca4S3. How many grams of S are needed to react with 2.50 g of Ca?



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9. Green plants produce glucose, C6H12O6, and molecular oxygen by photosynthesis of carbon dioxide and water: 6 CO2 + 6 H2O C6H12O6 + 6 O2 How many grams of CO2 are required to produce one mole of glucose? 10. KClO3 + 6 KBr + 3 H2SO4 KCl + 3 Br2 + 3 H2O + 3 K2SO4 a. How many moles of Br2 are produced when 0.80 moles of KBr reacts? b. How many moles of H2SO4 are needed to react with 3.7 grams of KClO3? c. If 300.0 grams of KClO3 and 400.0 grams of KBr are mixed with excess H2SO4, how much Br2 can be produced? 11. hat mass of SO3 is produced when 0.600 grams of SO2 is combined with 0.400 grams of O2? 2 SO2 + O2 2 SO3 12. Hydrogen gas combines with nitrogen dioxide to produce ammonia (NH3) and water. What mass of ammonia results when 25.0 g of hydrogen combines with 185 grams of nitrogen dioxide? 13. Consider the combination reaction of carbon with oxygen gas to produce carbon dioxide. If 1.0 gram of carbon is mixed with 1.0 gram of oxygen gas� a. What is the limiting reagent? b. Calculate the amount of the non-limiting reagent which remains unreacted after reaction is complete.

MOLE CONCEPT -- EUDIOMERTY 1. A hydrocarbon contains 10.5 g of carbon per g of H. One litre vapours of hydrogen at 127C and I atm pressure weights 2.8 g. Find molecular formula of hydrocarbon. 2. One litre of CO2 is passed over hot coke. The volume becomes 1.4 litre. Find the composition of products, assuming measurements at NTP. 3. 5 mL of a gaseous hydrocarbon was exposed to 30 mL of O2. The resultant gas, on cooling is found to measure 25 mL of which 10 mL are absorbed by NaOH and the reminder by pyrogallol. Determine molecular formula of hydrocarbon. All measurements are made at constant pressure and temperature. 4. When a mixture of 10 mole of SO2, 15 mole of O2 was passed over catalyst, 8 mole of SO3 was formed. How many mole SO2 and O2 did not enter into combination? 5. A mixture of 20 mL of CO, CH4 and N2 was burnet in excess of O2 resulting in reduction of 13 mL of volume. The residual gas was then treated with KOH solution to show a contraction of 14 mL in volume. Calculate volume of CO CH4 and N2 in mixture, all measurements are made at constant pressure and temperature. 6. 50Ml of dry ammonia gas was sparked for a long time in an eudiometer tube over mercury. After sparking, the volume becomes 97 ml. After washing the gas with water and drying, the volume becomes 94 ml. This was mixed with 60.5 ml of oxygen and the mixture was burnt. After the completion of the combustion of H2, the volume of the residual gas was 48.75 ml. Determine molecular formula of ammonia. 7. The percentage by volume of C3H8 in a mixture C3H8, CH4 and CO is 36.5. Calculate the volume of CO2 produced when 100 ml of the mixture is burnt in excess of O2. 8. 100 mL of any gas at NTP was heated with Tin. Tin converted into stannous sulphide and hydrogen was left. The hydrogen when passed over hot CuO, produced 0.081 g of water. If the vapour density of the gas is 17, find its formula. 9. A gaseous alkane is exploded with oxygen. The volume of O2 for complete combustion to CO2 formed is in the ratio of 7 : 4. Deduce molecular formula of alkane. 10. 40 ml ammonia gas taken in an eudiometer tube was subjected to sparks till the volume did not further change. The volume was found to increase by 40 ml. 40ml of oxygen was then mixed than the mixture was further exploded. The gases remained were 30 ml. Deduce formula of ammonia. All measurements are made at constant P and T. Assume H2O in liquid phase. 11. The weight of one lt. sample of ozonised oxygen at NTP was found to be 1.5 g. When 100 ml of this mixture at NTP were treated with terpentine oil, the volume was reduced to 90 ml, Hence calculate the molecular weight of Ozone.



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12. 60 ml of a mixture of nitrous oxide and nitric oxide was exploded with excess of hydrocarbon. If 8 ml of N2 was formed, calculate the volume of each gas in mixture. All measurements are made at constant P and T. Assume H2O in liquid phase. 13. 50 ml of pure and dry oxygen was subjected to a silent electric discharge and on cooling to the original temperature, the volume of ozonised oxygen was found to be 47 ml. The gas was then brought into contact with terpentile oil, when after the absorption of ozone, the remaining gas occupied a volume of 41 ml. Find molecular formula of ozone. All measurements are made at constant P and T. 14. A sample of gaseous hydrocarbon occupying 1.12 lt. at NTP, when completely burnt in air produced and 1.8 g H2 O. Calculate the weight of hydrocarbon taken and the volume of O2 at NTP required for its combustion. 15. 16 ml of a gaseous aliphatic compound CnH3nOm was mixed with 60 ml O2 and sparked. The gas mixture on cooling occupied 44 ml. After treatment with KOH solution, the volume of gas remaining was 12 ml. Deduce the formula of compound. All measurements are made at constant pressure and room temperature. 16. A 5.0 g sample of a natural gas consisting of CH4, C2H4 was burnt in excess of oxygen yielding 14.5 g CO2 and some H2O as products. What is weight percentage of CH4 and C2H4 in mixture? 17. 4 g C3H8 and 14 g O2 are allowed to react to the maximum possible extent to form only CO and H2O. Find the weight of CO formed. 18. A mixture of C2H4 and excess of hydrogen has a pressure of 60 cm of Hg. The mixture on passing over Ni Catalyst gives. C2H4 (g) +H2(g) C2H6(g) The pressure of resultant mixture under original conditions of temperature and volume reduced to 40 cm of Hg. Calculate the fraction occupied by C2H4 in original mixture. 19. A mixture of methane and ethylene in the volume ratio X: Y has a total volume of 30 ml. On complete combustion it gave 40 ml of CO2. If the ratio had been Y: X, instead of X : Y ,what volume of CO2 would have been obtained. 20. 1 volume of gaseous compound C, H, O on complete combustion in presence of 2.5 volume of O2 gives 2 volume of steam and 2 volume of CO2. What is the formula of compound if all measurements are made at STP? Also calculate volume of O2 required to burn completely 4.4 g of this compound. 21. At the Nangal fertilizer plant in Punjab, hydrogen is produced by the electrolysis of water. The hydrogen is used for the production of NH3 and HNO3 (by oxidation of NH3). If the average production of ammonium nitrate is 5000 kg per day, estimate the daily consumption of electricity per day. 22. 10 ml of gaseous organic compound C, H and O only was mixed with 100 ml of O2 and exploded under identical conditions and then cooled. The volume left after cooling was 90 ml. On treatment with KOH a contraction of 20 ml was observed. If vapour density of compound is 23 ,derive molecular formula of compound. 23. 100 ml of CH4 and C2H2 were exploded with excess of O2. After explosion and cooling, the mixture was treated with KOH, where a reduction of 165 ml was observed. Find composition of mixture in 100 ml. 24. 200 ml of a mixture of CH4 and C2H2 were exploded with 800 ml. of O2. After explosion and cooling, the volume was found to be 600 ml. After treatment with KOH, the final volume was found to be 260 ml. Find the composition of mixture if all measurements are made at NTP. Also calculate mole of CO2 formed. 25. On passing 25 ml of a gaseous mixture of N2 and NO over heated Cu, 20 ml of gas remained. Calculate the percentage of each in mixture.



31

26. Calculate the volume of CO2 produced by the combustion of 40 ml of acetone vapours in presence of excess of oxygen. 27. What volume of air at NTP will be required to oxide 210 ml of SO2 at NTP to sulphur trioxide, if the air contains 21 % of O2? 28. What volume of air is needed for the composition of 1 meter3 of a gas having the following composition in percentage volume; 50% of H2, 35% of CH4, 8% of CO, 2% of C2H4 and 5%of non combustible mixture? The air contains 21% of oxygen. 29. A natural gas sample contains 84% (by volume) of CH4, 10% of C2H6, 3% N2. If a series of catalytic reactions could be used for converting all the carbon atoms into butadiene, C4H6, with 100% efficiency how much butadiene could be prepared from 100 g of the natural gas? 30. 16 ml of hydrocarbon gas was exploded with excess of oxygen. On cooling, the volume of resulting gaseous mixture was reduced by 48 ml. When KOH was added, there was a further decrease of 48 ml in volume. Find the molecular formula of compound. 31. 60 ml of a mixture of nitrous oxide and nitric oxide was exploded with excess of hydrogen. If 38 ml of N2 was formed, calculate the volume of each other gas in the mixture. 32. 20 ml of gas containing H and S was heated with tin. When the reaction was over, there was no change in volume. The residual gas was hydrogen. If the molecular weight of the gas is 34, calculate the molecular formula of gas. 33. A mixture of oxygen and hydrogen is analysed by passing it over hot copper oxide and through an drying tube. Hydrogen reduces the CuO according to the equation: CuO +H2 Cu +H2O. Oxygen then oxidises the copper formed: Cu+1/2 O2 CuO. 100 cm3 of the mixture measured at 25C and 750 mm yield 84.5 cm3 of dry oxygen measured at 25C and 750 mm after passing over CuO and drying agent. What is the mole percent of H2 in the mixture? 34. 15 ml of a gaseous hydrocarbon required for complete combustion 357 ml of air containing O2, 21 % by volume and the gaseous products occupied 327 ml. If all volumes are measured at STP find out formula of hydrocarbon. ANSWERS: 1. Molecular Formula = C7H8 2. CO2= 0.6 lt. CO = 0.8 lt. 3. C2H4 4. Mole of SO2= 2 5.CO = 10 ML , CH4 = 4 Ml, N2 = 6 Ml Mole of O2 = 11 6. NH3 7. CO2 = 173 ml 8. Thus gas is H2S 9. Alkane is C2H6 10. Ammonia = NH3 11. Molecular wt. of O3 = 48.2 12. NO= 44 ml, N2O = 16 ml 13. Molecular formula is O3 14. CH4 = 0.8 g, O2 = 2.24 lt. 15. n = 2 ,m =1 16. C2H4 = 39.2 % CH4 = 60.8 % 17. CO = 7.636 g 18. 1/3 19. 50 ml 20. C2H4O, 5.6 lt. O2 21. 3.618 X1010 coulomb 22. C2H6O 23. CH4 = 35 ml, C2H2 = 65 ml 24. CH4 = 30%, C2H% = 70 %, CO2 = 0.015 mole 25. N2 = 60%, NO = 40% 26. 120 ml 27. 500 ml. 28. 5 Cubic meter. 29. 82 g. 30. C3H8 31. NO = 44 ml, N2O = 16 ml 32. H2S 33. 10.33% 34. C3H8

er



32

1. To the correct number of significant figures, (5.0 x 10-5)÷(2.00 x 10-2) is

2.50 x 104 2.5 x 10-7 2.5 x 10-4 2.5 x 10-3 2.50 x 10-3 none of these

4. Which of the following measurements are equivalent?

10 micrograms and 0.1 milligrams 10 nL and 1000 pL

40 km and 40000 cm 0.01 mm and 1 x 10-3 cm

all of these none of these

6. Which of the following lists of elements contains an alkaline earth metal, a transition metal, and a halogen, respectively?

Rb, Y, I Ba, Fe, Br Sr, Zr, Xe K, Ni, O none of these all of these

7. A beam of particles is passed between a positively charged and a negatively charged plate. The beam splits into three parts while passing between the plates. Beam A is slightly deflected towards the negatively charged plate; Beam B is strongly deflected towards the positively charged plate, and beam C is undeflected. Which of the following conclusions is correct?

1. Particles in beam A are positively charged.

2. B particles are more massive than A particles.

3. C particles are negatively charged.

1 and 3 2 only 3 only 1 and 2 1 only 2 and 3

9. Bromine has two common isotopes, 79Br and 81Br. Which is the following statements is true? 81Br has two more electrons than 79Br. 81Br has two more protons than 79Br. 81Br has two more neutrons than 79Br.

79Br has 79 neutrons. 79Br has 35 electrons and 44 protons. none of these

10. The average atomic mass of Cl is 35.453. About 75% of all Cl atoms are 35Cl. If there is only one other common isotope, it is most likely to be 36Cl 37Cl 38Cl 34Cl 35.453Cl None of these

11. Which of the following compounds are correctly named?

Cu(HCO3)2, copper (II) bicarbonate Ba3(PO4)2, tribarium diphosphate AgNO3, argentum nitrate

SrSO3, strontium sulfate FeCO3, iron (III) carbonate none of these

12. Cadmium (II) selenide can be used to prepare solutions which have almost any color in the spectrum. If the selenide ion is Se2-, the formula for this compound is

CdSe2 Cd2Se CdSe Cd2Se2 Cd-II-Se none of these

13. Which of the following is the formula for hydrosulfuric acid?

HS H2S H2SO2 H2SO3 H2SO4 HSO4

14. The following equation for the combustion of glucose is NOT balanced:

C6H12O6(s) + O2(g) = CO2(g) + H2O(l)

If the equation is balanced with smallest integer coefficients, the coefficient of O2(g) is

18 9 6 12 15 none of these

15. Mixing which of the following will produce a precipitation reaction?

none of these HNO3(aq) and Sr(OH)2(aq)

NaOH and KBr Zn and HCl

AgNO3 and NaClO4 Na2SO4(aq) and Ba(OH)2(aq)



33

16. Which of the following species are present in an aqueous acetic acid solution?

H3O+(aq) HC2H3O2(aq) C2H3O2

-(aq) all of these OH-(aq) H2O(l)

17. Which of the following is the net ionic equation for the reaction between hydrochloric acid and potassium hydroxide?

HCl(aq) + KOH(aq) = H2O(l) + KCl(aq) K+(aq) + Cl-(aq) = KCl(aq) K+(aq) + Cl-(aq) = KCl(s) K+(aq) + Cl-(aq) + H+(aq) + OH-(aq) = H2O(l) + K+(aq) + Cl-(aq) H3O

+(aq) + OH-(aq) = 2 H2O(l) HClO4(aq) + KOH(aq) = H2O(l) + KClO4(aq)

18. A well near the beach is suspected to be contaminated with chloride ions from sea water. If chloride is present, which of the following will produce a cloudy suspension when mixed with the water?

LiBr NaNO3(aq) KC2H3O2(aq) AgNO3(aq) acetic acid none of these

19. Ammonium nitrate is used as a nitrogen fertilizer. What is the percentage of nitrogen by mass in ammonium nitrate? (The atomic weights of N, H, and O are 14.0, 1.0, and 16.0, respectively.)

43.8% 35.4% 17.5% 42.9% 35.0% none of these

20. A compound of sulfur and oxygen is 40.1% sulfur by mass. What is the empirical formula for the compound? The atomic weights of S and O are 32.07 and 16.00, respectively.

SO SO4 SO2 S2O3 SO3 none of these

21. The first step in an analysis of water for dissolved oxygen involves the reaction

4 Mn(OH)2(aq) + O2(aq) + 2 H2O(aq) = 4 Mn(OH)3(s)

.If treatment of 1.000 L of water from a creek with excess Mn(OH)2(aq) produces 0.103 g of Mn(OH)3, how many grams of O2(aq) does one liter of the water contain? The molecular weights of Mn(OH)2 and Mn(OH)3 are 88.94 and 105.94, respectively.

(0.103 x 32)/(88.94 x 4) (0.103 x 105.94 x 32)/4 (0.103 x 4 x 32)/105.94

(0.103 x 16)/(105.94 x 4) (0.103 x 32)/(105.94 x 4) (0.103 x 16)/(88.94 x 4)

22. Sucrose (table sugar) has empirical formula CH2O and molecular weight 360. The atomic weights of C, H, and O are 12, 1, and 16, respectively. The molecular formula of sucrose is

C6H12O6 C12H24O12 C360H720O360 CH2O C12H12O12 none of these

23. Oxygen gas is converted to ozone gas by exposure to intense ultraviolet light:

3 O2(g) = 2 O3(g)

If an ultraviolet source converts oxygen to ozone with a 4% yield, how many grams of oxygen are required to produce 1 gram of ozone? The atomic weight of O is 16.

1.5 g 0.04 g 1 g

25 g 0.06 g none of these

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2933413 Stoichiometry Mole Concept for Iitjee