Homework:

• Read Pages 58-61• Do all of % composition worksheet

• Mole problems 3 Packet• Next Quiz: Monday Feb 25 or Tues

Feb 26• Test: March 11th (Monday) or

March 12th (Tuesday)

Percent Composition Lesson 3

•Determining the formula of a compound % by mass of each element in a compound

% CompositionIf 8.20 grams of magnesium combines with 5.40 grams of oxygen to form a compound , what is the % composition of this compound?

% composition9.03 grams of Mg combine completely with 3.48 grams of nitrogen

% Composition of a known compound

compound of MM

cmpd. of mol 1in element of grams Element of Mass %

% composition of C3H8

% composition of each element in

sodium bisulfate

Homework

• Read: pages 59-61• Worksheet: Finding Empirical and

Molecular Formulas • More Mole problems WS II # 1-6• Test: March 11th and 12th

Mole Problems 31. 5.6 Liters2. 3.00 moles3. 8.03 grams4. 38.5 Liters5. 1.3 g/L

Mole Problems 41. 170 grams2. 2.53 grams3. 22.8 grams4. 2.75*1023 atoms5. 106 grams

Mole Problems 5

1. 9.21*1022 molecules NaOH2. 40.9 grams3. 2.07 L4. 3*10-23 grams

1. HCN 3. Ca(NO3)2

3.74% H 24.42% Ca 44.43% C 17.07% N 51.83% N 58.50% O2. H2O 4. Al2(CO3)3

11.21% H 23.06% Al 88.79% O 15.40% C

61.54% O

Percent Composition

More Mole ProblemsQuestion 1 Question 59.20 x 10-17 g 2.11 x 1023 atoms

Question 2 Question 60.5648 moles area = 0.00645

cm3

= 0.00645 mL

Question 3 3.89 x 1020 atoms

1.694 moles 1.02x1024 atomsQuestion 4

a) 2.1 x 1023 moleculesb) 183 g

More Mole ProblemsQuestion 7a)5.1 molb)1.86 x 1025 atomsc)182 mLQuestion 84.36x1016 moleculesQuestion 9

Finding Empirical and Molecular Formulas

Question 1 Question 4a) C3H4O3 CH2Cl

C2H4Cl2

b)CH2O Question 5c) CH2O C4H5N2OQuestion 2CH5N empirical CH5N molecularQuestion 3 Question 6P2O5 SN empirical;

S4N4 molecular

More Mole Problems Worksheet No.3 Answers• 2) STP: 0°C, 1 atm (760 mmHg, 101.3 kPa) • 3) 1.96 g/L• 4) 6.19 x 1022 molecules• 5) 20 moles• 6) 19.97%• 7.a) 5.78 x1022 atoms • 7.b) 0.384 g• 7.c) air: 1.25 g/L; bag: 1.365 g/L, bag will not

float• 8) 4.70%• 9) 5 glasses

Empirical Formula• Lowest whole number ratio of

atoms of the elements in a compound.

Calculate the empirical formula of a compound that is 25.9% nitrogen and 74.1% oxygen• Step 1: find mole ratio

• Step 2: divide by least # of moles

• Step 3: multiply to get a whole number

Molecular Formulas• Molecular formulas are whole

number multiples of the empirical formulas

• The empirical formula and the MM of the molecular formula is needed!

What is the empirical formula of a compound that is 27.3% C and 72.7% O?

Calculate the molecular formula given the empirical formula is CO2 and has a molar mass of 132.03 grams/mol

1. Find the MM of the empirical formula

2. Divide the MM of the molecular formula by the MM of the empirical formula

3. Multiply all elements by the whole # to get the molecular formula