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AP Chemistry Chapter 7

Stoichiometry

Name_______________
Period _________
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Elemental Composition
1. Calculate the mass percent of Cl in each of the following compounds:
a) ClF

b) HClO2

c) CuCl2

d) PuOCl

2. Calculate the percent composition of each of the following:

a) K2Fe(CN)6

b) BaSO3

c) KAlSi2O6

3. Which of the following formulas can NOT be empirical?

a) CH4 b) N2O5 c) Sb2S3
d) CH2 e) B2H6 f) N2O4
g) KMnO4 h) NH4Cl i) CH2O

4. Determine the empirical formula of a compound that contains the following percentages of elements
by mass: Mo = 43.95%, O = 7.33%, Cl = 48.72%

5. Determine the empirical and molecular formulas of a compound that has a mass of 31.04g/mole an
contains the following percentages of elements by mass: C=38.66%, H= 16.24%, N=45.10%
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6. A certain compound contains 26.35% C, 3.30% H and 70.35% O. If the molecular mass of this
compound is 819 g/mol, what are the empirical & molecular formulas of this compound?

7. Ribose is an important sugar found in RNA & DNA. Ribose has a molar mass of 150g/mol and a
chemical composition of 40.0% carbon, 6.67% hydrogen and 53.3% oxygen. What is the empirical
and molecular formula for ribose?

Formula of a Hydrate
8. Write the formula for the hydrate of CaSO4 that has a mass of 97.85 g before heating and 64.01 g
after heating.

9. 140.4 g of hydrated compound of MgSO4 was heated until it had a mass of 68.6 g. What is the
formula of the hydrate?

10. A hydrate of MgSO4 was heated intensely so that the mass changed from 2.389 g to 0.855 g. What
is the formula of the hydrate?

11. If 9.99 g of a hydrated CaCO3 are heated so that the mass then becomes 5.81 g, what is the formula
of the hydrate?
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Balancing Equations AP Chemistry

Convert the following word equations to balanced chemical equations.
1. aluminum hydroxide + sulfuric acid yields aluminum sulfate + water

2. sodium phosphate + calcium chloride yields calcium phosphate + sodium chloride

3. calcium hydroxide + phosphoric acid yield calcium phosphate + water

4. hydrogen + nitrogen monoxide yields water + nitrogen gas

5. iron metal + copper(II)sulfate  iron(III)sulfate + copper metal

6. calcium carbonate  calcium oxide + carbon dioxide gas

7. ammonium sulfate + barium chloride  ammonium chloride + barium sulfate

8. Write a balanced chemical equation for the reaction in which dinitrogen pentoxide reacts with water
to produce nitric acid.

9. Magnesium reacts with titanium (IV) chloride to produce magnesium chloride and titanium. Write
the balanced equation for this reaction.

10. Write a balanced chemical equation for the reaction in which carbon reacts with zinc oxide to
produce zinc and carbon dioxide.

11. Bromine reacts with sodium iodide to form sodium bromide and iodine. Write the balanced
equation for this reaction.

12. Write a balanced chemical equation for the reaction in which phosphorous trichloride reacts with
chlorine gas to produce phosphorous pentachloride.
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13. Calcium hydride reacts with water to produce calcium hydroxide and hydrogen gas. Write a
balanced chemical equation for the reaction.

14. Write a balanced chemical equation for the reaction in which sulfuric acid reacts with potassium
hydroxide to produce potassium sulfate and water.

15. Write a balanced chemical equation for the reaction in which propane (C3H8) reacts with oxygen
gas to produce carbon dioxide and water.

Balance the following reactions by adding coefficients:

1. ______ C4H10(g) + _______ O2(g)  _______ CO2(g) + ______ H2O(g)

2. ______ Ca(OH)2 + ______ H2SO4  ______ H2O + ______ CaSO4

3. ______ C5H12(g) + ______ O2(g)  ______ CO2(g) + ______ H2O(g)

4. ______ CoS(s) + ______ O2(g)  _____ CoO(s) + ______ SO2(g)

5. ______ C6H14(g) + ______ O2(g)  ______ CO2(g) + ______ H2O(g)

6. ______ Fe(s) + ______ O2(g)  ______ Fe2O3(s)

7. ______ La(NO3)3 + ______ NaOH  ______ La(OH)3 + ______ NaNO3

8. ______ Zn + ______ CrCl3  ______ CrCl2 + ______ ZnCl2

9. ______ HfCl3 + ______ Al  ______ HfCl2 + ______ AlCl3

10. ______ NH3(g) + ______ Cl2(g)  ______ NH4Cl(s) + ______ NCl3(g)

11. ______ BaCO3 + ______ C + ______ H2O  ______ CO + ______ Ba(OH)2

12. ______ Cu2S + ______ HNO3  ______ Cu(NO3)2 + ______ CuSO4 + ______ NO2 + ______ H2O

13. ______ CuSO4(aq) + ______ KI(s)  ______ CuI(s) + ______ I2(s) + ______ K2SO4(aq)

14. ______ MnO2(s) + ______ HCl(aq)  ______ MnCl2(aq) + ______ Cl2(g) + ______ H2O(l)

15. ______ Na2CO3(aq) + ______ S(s) + ______ SO2(g)  ______ CO2(g) + ______ Na2S2O3(aq)
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Stoichiometry
1. Several brands of antacid tablets use aluminum hydroxide to neutralize excess acid.
Al(OH)3(s) + 3 HCl(aq)  AlCl3(aq) + 3 H2O(l)
What quantity of HCl, in grams, can a tablet with 0.750 g of Al(OH)3 consume? What quantity of water is
produced?

2. If 10.0 g of carbon is combined with an exact, stoichiometric amount of oxygen (26.6 g) to produce carbon
dioxide, what mass, in grams, of CO2 can be obtained? That is, what is the theoretical yield of CO2?

3. The equation for one of the reactions in the process of reducing iron ore to the metal is
Fe2O3(s) + 3 CO(g)  2 Fe(s) + 3 CO2(g)
(a) What is the maximum mass of iron, in grams, that can be obtained from 454 g (1.00 lb) of iron(III) oxide?

(b) What mass of CO is required to reduce the iron(III) oxide to iron metal?

4. Burning coal and oil in a power plant produces pollutants such as sulfur dioxide, SO2. The sulfur-containing
compound can be removed from other waste gases, however, by the following reaction:
2 SO2(g) + 2 CaCO3(s) + O2(g)  2 CaSO4(s) + 2 CO2(g)
(a) Name the compounds involved in the reaction.

(b) What mass of CaCO3 is required to remove 155 g of SO2?

(c) What mass of CaSO4 is formed when 155 g SO2 is consumed completely?

5. Your body deals with excess nitrogen by excreting it in the form of urea, NH2CONH2. The reaction producing
it is the combination of arginine (C6H14N4O2) with water to give urea and ornithine (C5H12N2O2).
C6H14N4O2 + H2O  NH2CONH2 + C5H12N2O2
If you excrete 95 mg of urea, what quantity of arginine must have been used?
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Limiting Reactants
1. The reaction of methane and water is one way to prepare hydrogen: CH4(g) + H2O(g)  CO(g) + 3 H2(g)
If you begin with 995 g of CH4 and 2510 g of water, what is the maximum possible yield of H2?

2. Disulfur dichloride, S2Cl2, is used to vulcanize rubber. It can be made by treating molten sulfur with gaseous
chlorine: S8(l) + 4 Cl2(g)  4 S2Cl2(l)
Starting with a mixture of 32.0 g of sulfur and 71.0 g of Cl2, which is the limiting reactant? What mass of S2Cl2 (in
grams) can be produced?

3. Using the same reactants from the above reaction determine the mass of excess reactant remaining when the
limiting reactant is consumed?

Percent Yield
4. Diborane, B2H6, is a valuable compound in the synthesis of new organic compounds. One of several ways this
born compound can be made is by the reaction
2 NaBH4(s) + I2(s)  B2H6(g) + 2 NaI(s) + H2(g)
Suppose you use 1.203 g of NaBH4 with an excess of iodine and obtain 0.295 g of B2H6. What is the percent yield of
B2H6?

5. Disulfur dichloride, which has a revolting smell, can be prepared by directly combining S8 and Cl2, but it can also
be made by the following reaction:
3 SCl2(l) + 4 NaF(s)  SF4(g) + S2Cl2(l) + 4 NaCl(s)
Assume you begin with 5.23 g of SCl2 and excess NaF. What is the theoretical yield of S2Cl2? If only 1.19 g of
S2Cl2 is obtained, what is the percent yield of the compound?
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Combustion Analysis:

1. The molecular formula of a hydrocarbon is determined by analyzing its combustion products.

(a) The hydrocarbon burns completely, producing 7.2 grams of water and 14.14 grams of CO2. What is
the empirical formula of the hydrocarbon?

(b) Calculate the mass in grams of O2 required for the complete combustion of the sample of the
hydrocarbon described in (a).

2. A 15.00-g sample of an unknown hydrocarbon is analyzed by combustion analysis. The sample produced
50.70 grams of carbon dioxide and 10.42 grams of water. Find the empirical formula of the unknown.

3. The characteristic odor of pineapple is due to ethyl butyrate, a compound containing C, H and O. When 2.78
g of ethyl butyrate burns completely, it produces 2.58 g of water and 6.32 g of CO2. What is the empirical
formula of the compound?

4. A 15.00g sample of a compound containing carbon, hydrogen and nitrogen is analyzed by combustion
analysis. The sample produced 29.3 grams of carbon dioxide and 20.8 grams of water. Find the empirical
formula of this compound.
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Additional Pre-Test Practice

1. Calculate the percent water in cobalt III nitrate hexahydrate.

2. Find the mass percent of strontium dichromate.

3. Find the empirical formula for a compound containing 37.51 %Carbon, 4.20% Hydrogen, and 58.29% Oxygen.
Name the acid!

4. Determine the molecular formula for the compound whose empirical formula is OCNCl. The molecular mass of
the compound is 232.4 g/mol.

5. Aspirin (C9H8O4) is produced by the reaction of salicylic acid (C7H6O3) and acetic anhydride (C4H6O3).
C7H6O3(s) + C4H6O3(l)  C9H8O4(s) + CH3CO2H(aq)
If you mix 100. g of each of the reactants, what is the maximum mass of aspirin that can be obtained?

6. Nicotine, a component of tobacco, is composed of C, H and N. A 5.250 g sample of nicotine was combusted,
producing14.242 g of CO2 and 4.083 g of H2O. What is the empirical formula? If the substance has a molar
mass of 1605, what is its molecular formula?