Chem 4 - Sample Exam #2

Sample Exams are designed to give you an idea of the types of questions you can expect.  Exam numbers may not exactly agree with currently assigned material, so you may need to examine other sample exams to see questions that might be on the upcoming exam.

1. Complete the following statements:

The total number of atoms present before and after a chemical reaction takes place must be _equal___.

Name and write the formula for three strong acids that are used frequently in the laboratory

For example, nitric: HNO3, hydrochloric: HCl, sulfuric: H2SO4, phosphoric, H3PO4

Name and write the formula for two bases that are used frequently in the laboratory: Answer: NaOH & KOH

When an ionic compound dissolves, the solution contains __ions__ and is an electrolyte.

2. Write the correct formula for each of the following compounds:

potassium hydroxide _____________NaOH______________________

sodium carbonate _________Na2CO3______________

nitric acid _____HNO3 _____

cobalt(III) nitrate ______Co(NO3)3________

calcium chloride _______CaCl2_________

lead(IV) oxide ______PbO2__________

dinitrogen pentoxide ______N2O5________

ammonium chromate _______(NH4)2CrO4____

iron(II) chloride ________FeCl2________

barium sulfate _______BaSO4 ________

3. When you combine Na metal with water, there is a reaction. One of the products is a gas and the other is NaOH. Write the balanced equation. (Na + 2 HOH --> NaOH + H2 )What is the gas? ___hydrogen, H2_____.

4. Answer the following True/False questions:

_X_ T ___ F A weak acid is one that does not ionize very well

___ T _X_ F Since NaCl is ionic, it always conducts electricity, whether solid or in solution

___ T _X_ F All compounds containing the S2- ion are insoluble in water

___ T _X_ F Every reaction that undergoes oxidation uses oxygen as the oxidizing agent

_X_ T ___ F When an atom gains electrons, it is reduced and becomes an anion

___ T _X_ F When Zinc reacts with HCl, Cl2 and H2 gases are produced

___ T _X_ F For both CH4 and CO2, carbon has a valence of -4

___ T _X_ F Combustion reactions always product water and carbon monoxide

___ T _X_ F A decomposition reaction is the formation of water from H2 and O2

_X_ T ___ F The reaction between H+ and OH- is often called an acid-base reaction

_X_ T ___ F The ionic compound produced from an acid-base reaction is a salt

___ T _X_ F The mass percentage of hydrogen in water is 100%

___ T _X_ F The empirical formula is always different from the actual formula

___ T _X_ F For this reaction C + O2 à CO2, 1 gram of C reacts with exactly 1 gram O2

___ T ___ F Spectator ions love to watch Monday Night Football, and root for the home team

5. List 4 ways you can determine if a chemical reaction has occurred.

6. Show the products and balance the following reactions. Then, write the complete and net ionic equations for each.

Ca(NO3)2 (aq) + H2SO4 (aq)  à CaSO4 (s) + 2 HNO3 (aq)

Na2CO3 (aq) + CoCl2 (aq)  à 2 NaCl (aq) + CoCO3 (s)

7. Balance the following equations. If products are not shown, write the correct formulas yourself, and then balance the equation.

SiO2 + 4 HF  à SiF4 + 2 H2O

4 Co + 3 O2  à  2 Co2O3

4 NH3 +  5 O2 à 4 NO + 6 H2O

FeCl3 + KOH  à Fe(OH)3 + 3 KCl

3 H2 + N2 à 2 NH3

8. Write the balanced equation for the combustion (oxidation) of propane (C3H8) with O2.

C3H8 + 5 O2  à 3 CO2 + 4 H2O

9. The percentage composition of a new compound is 40% sulfur and 60% oxygen. What is its empirical formula? If this compound has molar mass of 160 grams. What is its actual formula?

Empirical formula: SO3

Actual formula: S2O6

10. Calculate the number of moles in 42.5 g phenol (C6H6O). Answer: 0.452 mol

11. What is the molar mass of:

CH4 ___16 g/mol ________

potassium sulfate ___135.1 g/mol ____

AgI ____  236.8 g/mol _____

sodium hydroxide ____40 g/mol ___

CO2 ___44 g/mol _____

sulfuric acid ___96 g/mol ___

12. Show the complete electron configuration for following elements (e.g. N = 1s2 2s2 2p3)

Ne = ___1s2 2s2 2p6________

Li = ____1s2 2s1 ___________

Br = ______ [Ar] 4s2 3d10 4p5 _____________

Cs = ______ [Xe] 6s1 _____________

13. You react Al with O2 to produce Al2O3. You start with 10 grams of Al and 20 grams of O2. Which reactant is limiting? _Al_ Based on the limiting reactant, how many grams of Al2O3 will you produce? 18.9 g Al2O3

14. How many electrons (2n2 ) will be in each of the first three principal energy levels? Show the names for the different electron orbitals present in each energy level.

# Subshells

Maximum # Electrons (2n2 )

Names of orbitals present (n2 )

Orbital names

n =1

1

2

1

s

n = 2

2

8

4

s, p

n = 3

3

18

9

s, p, d

EXTRA CREDIT (4 points): Do all oxidation reactions require oxygen? ____ Yes _X_ No

(i) Write an equation for the oxidation of Mg with O2. (ii) Show the reaction that occurs when you add this product to water. (These reactions were performed in the lab.)

(i) 2 Mg + O2 à 2 MgO

(ii) MgO + HOH à Mg(OH)2

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