Chemistry-Semester Exam Review

Module 1

• What is the difference between a scientific theory and law?

A scientific theory is a set of ideas that attempts to explain why things happen the way they do in the natural world. A law is a generalization that describes a variety of behaviors in nature, but does not attempt to explain.Examples: The theory of evolution and law of gravity.

• What makes science different from other fields of knowledge?

The scientific method which is a systematic approach to problem solving. Science is about observation to answer questions, unlike philosophy which does not need to be based upon observation.

• How many significant figures do each of terms these have?

• 0.005670 cm

• 1.00 cm

• 100 cm

• 100.00 cm

Answers

• 0.005670 cm (4 sig figs)

• 1.00 cm (3 sig figs)

• 100 cm (1 sig fig)

• 100.00 cm (5 sig figs)

Five rules of sig figs.

1.

2.

3.

4.

5.

Five Rules of sig figs

1. Every non-zero is significant.2. Any zero between non-zeroes is significant.3. Any zero at the beginning of a number before

the first non-zero is NOT significant.4. Any zero at the end of a number without a

decimal place is NOT significant.5. Any zero at the end of a number with a

decimal place is significant.

• When adding or subtracting sig figs, you need to find the lowest number decimal places and then add or subtract and round your answer to that number of decimal places.

• ex: 1.005 + 2.0074 =

• ex: 1.005 - 2.0074 =

Rules of sig figs for addition and subtraction.

Answers

• ex: 1.005 + 2.0074 = 3.0124 rounded to 3.012 (three decimal places)

• ex: 1.005 - 2.0074 = -1.0024 rounded to -1.002 (three decimal places)

When multiplying or dividing sig figs, you need to find the lowest number of significant figures and then multiplying and dividing and round your answer to that number of significant

figures.

• ex: 1.005 * 2.0074 =

• ex: 1.005 / 2.0074 =

Answers

• ex: 1.005 * 2.0074 = 2.017437 rounded to 2.017 (four significant figures)

• ex: 1.005 / 2.0074 = 0.500647603865697 rounded to 0.5006 (four significant figures)

Unit Conversion.

• Can you convert 56.5 km to m?

Answer

56.5 km 1000 m = 56500 m 1 km

Can you convert 56.5 km to m?

Unit Conversion

• 500.5 ml to liters?

Answer

• 500.5 ml to liters?

500.5 mL 1 x 10-3 L = 0.5005 1 mL

Chemistry Semester Exam Review

Module 2

Why do theories change and evolve?

A. No one believes the original theory.B. New technology or experimentation leads to

revised ideas.C. If one scientist makes a discovery that

challenges a theory it will change the theory.D. If certain important groups of people think

that the theory is wrong, the theory will be considered invalid.

Why do theories change and evolve?

A. No one believes the original theory.B. New technology or experimentation leads to

revised ideas.C. If one scientist makes a discovery that

challenges a theory it will change the theory.D. If certain important groups of people think

that the theory is wrong, the theory will be considered invalid.

What are models? Why do scientists use them?

A. Models are useful for scientists that can’t collect real data

B. Models allow scientists to predict reactions without making real life observations.

C. Models are used as visual representations of something very small or very large. Something that isn’t easy to see or observe.

D. Models help scientists study things without having to conduct experiments or collect data.

What are models? Why do scientists use them?

A. Models are useful for scientists that can’t collect real data

B. Models allow scientists to predict reactions without making real life observations.

C. Models are used as visual representations of something very small or very large. Something that isn’t easy to see or observe.

D. Models help scientists study things without having to conduct experiments or collect data.

• Describe the main points of Dalton’s atomic theory and what points have changed as a result of experiments performed later. Include details of those experiments such as their expected and observed results and the scientists credited with those discoveries.

• Dalton’s Theory:• All matter is composed of extremely small particles called atoms.• Atoms of a given element are identical in size, mass and other properties.

• Scientists now know that all atoms of a given element have the same number of protons but may have different numbers of neutrons (isotopes).

• Atoms cannot be subdivided, created, or destroyed.• Scientists now know that atoms are divisible and made up of smaller, subatomic

particles. However, the law of conservation of mass still states that matter cannot be created or destroyed in an ordinary chemical reaction.

• Atoms of different elements can combine in simple, whole-number ratios to form chemical compounds.

• In chemical reactions, atoms are combined, separated, or rearranged. • Others/Changes:• The cathode ray experiments resulted in Thomson adding electrons to the atomic model.• Rutherford’s gold foil experiment disproved Thomson’s plum pudding model by demonstrating

that the mass of an atom is packed into a small, positive nucleus. He added the nucleus to the model of that atom, surrounded by electrons.

• Bohr’s observation of the line spectra led to his idea that electrons exist on orbits around the nucleus, which he added to the model of the atom.

• Schrodinger’s quantum model resulted from experiments that demonstrated the dual nature of light and the electron. He added energy levels and orbitals to the electron cloud surrounding the nucleus.

• A neutral atom has the atomic number 14 and a mass number of 31, how many protons, neutrons, and electrons are found within the atom?

• A neutral atom has the atomic number 14 and a mass number of 31, how many protons, neutrons, and electrons are found within the atom?

Protons: 14, neutrons : 17 (31-14 = 17), electrons : 14

• An atom is determined to contain 8 protons, 10 electrons, and 9 neutrons. What are the atomic number, mass number and charge of this atom or ion?

A. atomic number: 8 mass number: 17, charge: -2B. atomic number 9, mass number: 27, charge:

neutral +1C. atomic number 10, mass number: 17, charge: +2D. atomic number 8, mass number: 27, charge: -2

• An atom is determined to contain 8 protons, 10 electrons, and 9 neutrons. What are the atomic number, mass number and charge of this atom or ion?

A. atomic number: 8 mass number: 17, charge: -2B. atomic number 9, mass number: 27, charge:

neutral +1C. atomic number 10, mass number: 17, charge: +2D. atomic number 8, mass number: 27, charge: -2

• How many grams of carbon (C) are present in a sample of 2.5 × 1024 atoms C?

• How many grams of carbon (C) are present in a sample of 2.5 × 1024 atoms C?

• 49.9 g C

Which of the following contains the greatest number of moles?

A. 6.02 × 1023 atoms AgB. 5.1 mol AgC. 0.3 mol FeD. 125 g Fe

Which of the following contains the greatest number of moles?

A. 6.02 × 1023 atoms AgB. 5.1 mol AgC. 0.3 mol FeD. 125 g Fe

When an element is heated in a Bunsen burner flame, the resulting color of the flame changes can be used to identify the element. What causes the colored light that is observed?

When an element is heated in a Bunsen burner flame, the resulting color of the flame changes can be used to identify the element. What causes the colored light that is observed?

When an electron moves from a higher to lower orbital, energy is released as waves of light.

What occurs when an excited electron returns to its ground state?

A. Protons are releasedB. Energy is emitted as photons of lightC. It transfers to another atomD. The electron is no longer able to bond

What occurs when an excited electron returns to its ground state?

A. Protons are releasedB. Energy is emitted as photons of lightC. It transfers to another atomD. The electron is no longer able to bond

• How are the frequency, wavelength and energy of an electromagnetic wave related?

• As frequency __________, energy __________• As wavelength _________, energy __________• As frequency _________, wavelength

_________

• How are the frequency, wavelength and energy of an electromagnetic wave related?

• As frequency increases, energy increases• As wavelength increases, energy decreases• As frequency increases, wavelength decreases

What would be the most likely charge of an ion formed from an atom with the electron configuration: 1s2 2s2 2p5

• A. +2B. -2C. +1D. -1

What would be the most likely charge of an ion formed from an atom with the electron configuration: 1s2 2s2 2p5

• A. +2B. -2C. +1D. -1

Chemistry Semester One Exam Review

Module 3

Periodic Trends

1). Atomic radius/atomic size.

2). Ionization energy

3). Electronegativity

Periodic Trends1). Atomic radius/atomic size. There is a gradual decrease in atomic radii from left to right across a period.

There is a general increase in atomic radii going down each group of elements on the periodic table.

2). Ionization energy Ionization energy has a general increase for elements across a period from left to

right.

The ionization energy of elements decreases going down a group because the atomic radius of the atoms increases

3). Electronegativity Electronegativity increases from left to right across a period because of the increase

in effective nuclear charge.

Electronegativity decreases down a group, as a result of increased distance between the valence electrons and the nucleus (greater atomic radius).

Write the name of the following compounds

• CO2

• Ba3(PO4)2

• CuO • CaSO4 5H2O,

Write the name of the following compuonds

• CO2 carbon dioxide

• Ba3(PO4)2 barium phosphate

• CuO copper (II) oxide • CaSO4 5H2O calcium sulfate pentahydrate

Write the formula of the following compounds

1). magnesium phosphide

2). iodine dichloride

3). nitric acid

4). tin (IV) nitrate

5). potassium nitrate tetrahydrate.

Write the formula of the following compounds

1). magnesium phosphide Mg3P2

2). iodine dichloride ICl2

3). nitric acid HNO3

4). tin (IV) nitrate Sn(NO3)4

5). potassium nitrate tetrahydrate KNO3 3H2O

Which compound will experience hydrogen bonding?

A. HCl

B. C6H6

C. HF

D. H2SO4

Which compound will experience hydrogen bonding?

A. HCl

B. C6H6

C. HF

D. H2SO4

Draw Lewis Dot Structures for the following compounds

• HCN

• H2O

• O3

Chemistry Semester One Exam ReviewModule 4

Chemical Equations

Because of the principle of the conservation of matter, an equation must be

balanced.It must have the same number of atoms of the same kind on both sides.

Lavoisier, 1788

Chemical EquationsTheir Job: Depict the kind of

reactants and products and their relative amounts in a reaction.

4 Al (s) + 3 O2 (g) ---> 2 Al2O3 (s)

The numbers in the front are called

stoichiometric ____________The letters (s), (g), and (l) are the

physical states of compounds.

Balancing Equations

When balancing a chemical reaction you may add coefficients in front of the compounds to balance the reaction, but

you may not change the

subscripts.Changing the subscripts changes the compound. Subscripts are determined by the valence electrons (charges for ionic or sharing for covalent)

Steps to Balancing EquationsThere are four basic steps to balancing a chemical equation.

1. Write the correct formula for the reactants and the products. DO NOT TRY TO BALANCE IT YET! You must write the correct formulas first. And most importantly, once you write them correctly DO NOT CHANGE THE FORMULAS!

2. Find the number of atoms for each element on the left side. Compare those against the number of the atoms of the same element on the right side.

3. Determine where to place coefficients in front of formulas so that the left side has the same number of atoms as the right side for EACH element in order to balance the equation.

4. Check your answer to see if:The numbers of atoms on both sides of the equation are

now balanced.The coefficients are in the lowest possible whole number

ratios. (reduced)

Balancing Equations

___ H2(g) + ___ O2(g) ---> ___ H2O(l)

___ Al(s) + ___ Br2(l) ---> ___ Al2Br6(s)

Combination (Synthesis) Reactions

Two or more substances combine to form a new compound.

A + X AX

Reaction of elements with oxygen and sulfur Reactions of metals with Halogens Synthesis Reactions with Oxides There are others not covered here!

Decomposition Reactions

A single compound undergoes a reaction that produces two or more simpler substances

Decomposition of:   Binary compounds H2O(l ) 2H2(g) +

O2(g)   Metal carbonates CaCO3(s) CaO(s) +

CO2(g)   Metal hydroxides Ca(OH)2(s) CaO(s) +

H2O(g)   Metal chlorates 2KClO3(s) 2KCl(s) +

3O2(g)   Oxyacids H2CO3(aq) CO2(g) + H2O(l

)

AX A + X

Single Replacement Reactions

Replacement of:

Metals by another metal Hydrogen in water by a metal Hydrogen in an acid by a metal Halogens by more active halogens

A + BX AX + B

BX + Y BY + X

The Activity Series of the Metals

  Lithium   Potassium   Calcium   Sodium   Magnesium   Aluminum   Zinc   Chromium   Iron   Nickel   Lead   Hydrogen   Bismuth   Copper   Mercury   Silver   Platinum   Gold

Metals can replace other metals provided that they are above the metal that they are trying to replace.

Metals above hydrogen can replace hydrogen in acids.

Metals from sodium upward can replace hydrogen in water

The Activity Series of the Halogens

  Fluorine   Chlorine   Bromine   Iodine

Halogens can replace other halogens in compounds, provided that they are above the halogen that they are trying to replace.

2NaCl(s) + F2(g) 2NaF(s) + Cl2(g)

MgCl2(s) + Br2(g) ??? No Reaction

???

Double Replacement Reactions

The ions of two compounds exchange places in an aqueous solution to form two new compounds.

AX + BY AY + BX

One of the compounds formed is usually a precipitate, an insoluble gas that bubbles out of solution, or a molecular compound, usually water.

Combustion Reactions

A substance combines with oxygen, releasing a large amount of energy in the form of light and heat.

  Reactive elements combine with oxygen

P4(s) + 5O2(g) P4O10(s)

(This is also a synthesis reaction)

  The burning of natural gas, wood, gasoline

C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(g)

Stoichiometry

Sherlock Holmes, in Sir Arthur Conan Doyle’s A Study in Scarlet

“In solving a problem of this sort, the grand thing is to be able to reason backward. This is a very useful accomplishment, and a very easy one, but people do not practice it much.”

Stoichiometry - The study of quantities of materials consumed and produced in chemical reactions.

Review: Chemical Equations

Chemical change involves a reorganization of

the atoms in one or more substances.C2H5OH + 3O2 ® 2CO2 + 3H2O

reactants products

1 mole of ethanol reacts with 3 moles of oxygen to produce 2 moles of carbon dioxide and 3 moles of water

When the equation is balanced it has quantitative significance:

Review: Chemical Equations

Mole Relations

Mole Relations from Chemical Equations

Calculating Masses of Reactants and Products

1. Balance the equation. 2. Convert mass to moles. 3. Set up mole ratios. 4. Use mole ratios to calculate moles

of desired substituent. 5. Convert moles to grams, if

necessary.

Working a Stoichiometry Problem

6.50 grams of aluminum reacts with an excess of oxygen. How many grams of aluminum oxide are formed.

1. Identify reactants and products and write the balanced equation.

Al + O2 Al2O3

b. What are the reactants?

a. Every reaction needs a yield sign!

c. What are the products?

d. What are the balanced coefficients?

4 3 2

Working a Stoichiometry Problem

6.50 grams of aluminum reacts with an excess of oxygen. How many grams of aluminum oxide are formed?

4 Al + 3 O2 2Al2O3

=6.50 g Al

? g Al2O3

1 mol Al

26.98 g Al 4 mol Al

2 mol Al2O3

1 mol Al2O3

101.96 g Al2O3

6.50 x 2 x 101.96 ÷ 26.98 ÷ 4 =

12.3 g Al2O3

Limiting Reactant

The limiting reactant is the reactant

that is consumed first, limiting the amounts of products formed.

Limiting Reagents - Combustion

Limiting Reagents

Solving for Limiting Reactant

What is the limiting reactant if 6.50 grams of aluminum reacts with 8.97 g of water to produce 14.5 g Al2O3? Show, or explain, all of the steps that you used to solve this problem.

2Al + 3H2O Al2O3 + 3H2

=6.50 g Al 1 mol Al

26.98 g Al 2 mol Al

1 mol Al2O3

1 mol Al2O3

101.96 g Al2O3

=8.97 g H2O 1 mol H2O

18.0 g H2O 3 mol H2O

1 mol Al2O3

1 mol Al2O3

101.96 g Al2O3

? g Al2O3

? g Al2O3

Solving for Percent YieldTheoretical Yield

The maximum amount of a given product that can be formed when the limiting reactant is completely consumed

The actual yield (amount produced) of a reaction is usually less than the maximum expected (theoretical yield).Percent Yield

The actual amount of a given product as the percentage of the theoretical yield

Solving for Percent Yield

From the answers that you got from the problem on limiting reactants, (what is the limiting reactant if 6.50 grams of aluminum reacts with 8.97 g of water to produce 14.5 g Al2O3), determine the theoretical yield and the percent yield.