AP Chemistry Practice Problems
Module 2: Stoichiometry
The headings on these problems correspond to the headings on your content pages. You should work on
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Module 2: Stoichiometry Practice Problems dropbox according to your schedule.
Naming and Writing Formulas and Molecules
1. Name the following molecular compounds:
a. ClF3
b. S2Cl2
c. N2O5
d. AsCl5
2. Name the following ionic compounds:
a. NaF
b. Mg2C
c. Li3N
d. Al2O3
e. K2Se
3. Name the following ionic compounds.
a. Mn2O3
b. Hg2Cl2
c. PbS
d. CrCl3·4H2O
4. Name the following.
a. K3PO4
b. NH4C2H3O2
c. Fe2(CO3)3
d. Na2S2O3·5H2O
5. What are the formulas (including charges) for
(a) cyanide ion
(b) ammonium ion
(c) nitrate ion
(d) sulfite ion
(e) chlorate ion
(f) sulfate ion
6. What are the names of the following ions?
(a) Cr2O7-2
(b) OH−
(c) CH3COO−
(This can also be written as C2H3O2-.
You should recognize this in either
form.)
(d) CO3−2
(e) CN−
(f) ClO4−1
7. Identify each of the following as molecular or ionic and give its name.
a. V(NO3)3
b. Co(C2H3O2)2
c. Au2S3
d. Au2S
e. GeBr4
f. K2CrO4
g. Fe(OH)2
h. I2O4
i. I4O9
j. P4Se3
8. Write formulas for the following.
a. dialuminum hexachloride
b. tetraarsenic decaoxide
c. magnesium hydroxide
d. copper(II) bisulfate
e. ammonium thiocyanate
f. potassium thiosulfate
g. diiodine pentaoxide
9. Write formulas for the following.
a. mercury(II) acetate
b. barium hydrogen sulfite
c. boron trichloride
d. calcium phosphide
e. magnesium dihydrogen phosphate
f. calcium oxalate
g. xenon tetrafluoride
Dimensional Analysis
Problems are in the sidebar of the content. You do not have to submit those. But, you do need to practice
them and check the answers (also in the sidebar). You will have similar problems on your assessments.
The Mole, Mole Ratio, Mole and Mass
10. How many moles of nitrogen molecules correspond to 1.80 × 1024 molecules of N2?
11. How many moles of vanadium atoms, V, are needed to combine with 0.565 mol of O atoms to make
vanadium pentoxide, V2O5?
12. How many atoms are in 1.50 mol of carbon-12? How many grams does this much carbon-12 weigh?
13. Determine the mass in grams of each of the following:
a. 0.546 mol S
b. 3.29 mol N
c. 8.11 mol Al
14. Calculate the formula mass of each of the following and round your answer to the nearest 0.1 u:
a. Ca(NO3)2
b. Na2SO4·10H2O
c. Fe4[Fe(CN)6]3
15. What is the mass in grams of the following?
a. 0.754 mol ZnCl2
b. 0.194 mol KIO3
c. 0.322 mol POCl3
d. 4.31 × 10−3 mol (NH4)2HPO4
16. Calculate the number of moles of each compound in the following samples:
a. 9.36 g Ca(OH)2
b. 38.2 g PbSO4
17. The number of silicon atoms in 42.1 g of silicon is ______________.
18. 11.6 g of CuCl2 = _______________ moles CuCl2
19. What is the mass in grams of 9.31 x 1021 atoms of carbon?
20. 2.86 f.u. MgO = ________________ moles MgO
21. How many grams of sodium is equal to 6.92 x 1021 atoms of sodium?
Writing and Balancing Equations, Balanced Equations and Mole Ratios, Diatomic Molecules, Hydrates
22. Write chemical formulas for the elements that normally exist in nature as diatomic molecules.
23. Write correct balanced equations for the reactions between (a) calcium and chlorine, (b) magnesium and
oxygen, (c) aluminum and oxygen, and (d) sodium and sulfur.
24. Balance the following equations:
a. Mg(OH)2 + HBr → MgBr2 + H2O
b. HCl + Ca(OH)2 → CaCl2 + H2O
c. Al2O3 + H2SO4 → Al2(SO4)3 + H2O
d. KHCO3 + H3PO4 → K2HPO4 + H2O + CO2
e. C9H20 + O2 → CO2 + H2O
Reaction Stoichiometry
25. The octane in gasoline burns according to the following equation:
a.
b.
c.
d.
How many moles of O2 are needed to react fully with 6 mol of octane?
How many moles of CO2 can form from 0.5 mol of octane?
How many moles of water are produced by the combustion of 8 mol of octane?
If this reaction is used to synthesize 6.00 mol of CO2, how many moles of oxygen are needed? How
many moles of octane?
26. In dilute nitric acid, HNO3, copper metal dissolves according to the following equation:
How many grams of HNO3 are needed to dissolve 11.45 g of Cu according to this equation?
27. How many moles of UF6 would have to be decomposed to provide enough fluorine to prepare 1.25 mol of
CF4? (Assume sufficient carbon is available.) The equations have been provided below.
UF6  U + 3F2
2F2 + C  CF4
Percent Composition, Empirical and Molecular Formulas
28. Calculate the percentage composition by mass of each of the following: (a) (CH3)2N2H2 (b) Al2(SO4)3.
29. What are the empirical formulas of the following compounds? (a) C2H4(OH)2, (b) H2S2O8, (c) C4H10, (d) B2H6,
(e) C2H5OH.
30. A sample of Freon, a gas once used as a propellant in aerosol cans, was found to contain 0.423 g of C,
2.50 g Cl, and 1.34 g F. What is the empirical formula of this compound?
31. One compound of mercury with a formula mass of 519 contains 77.26% Hg, 9.25% C, and 1.17% H (with
the balance being O). Calculate the empirical and molecular formulas.
32. When 0.684 g of an organic compound containing only carbon, hydrogen, and oxygen was burned in
oxygen, 1.312 g CO2 and 0.805 g H2O were obtained. What is the empirical formula of the compound?
33. The following are empirical formulas and the masses per mole for three compounds. What are their
molecular formulas?
a. Na2SiO3; 732.6 g/mol
b. NaPO3; 305.9 g/mol
34. A sample of a compound of mercury and bromine with a mass of 0.389 g was found to contain 0.111 g
bromine. Its molecular mass was found to be 561. What are its empirical and molecular formulas?
Empirical Formulas of Hydrates, Molecular Formulas
35. Water is added to 4.267 grams of UF6. The only products are 3.730 grams of a solid containing only
uranium, oxygen, and fluorine and 0.970 gram of a gas. The gas is 95.0 percent fluorine, and the remainder
is hydrogen.
a. From these data, determine the empirical formula of the gas.
b. What fraction of the fluorine of the original compound is in the solid and what fraction in the gas after
the reaction?
c. What is the formula of the solid product?
d. Write a balanced equation for the reaction between UF6 and H2O. Assume that the empirical formula of
the gas is the true formula.
Limiting Reactants
36. 10 HI + 2 KMnO4 + 3 H2SO4 → 5 I2 + 2 MnSO4 + K2SO4 + 8 H2O
How many moles of HI would be necessary to produce 2.5 mol of I2, starting with 4.0 mol of KMnO4 and
3.0 mol of H2SO4?
a) 20
b) 10 c) 8.0 d) 5.0 e) 2.5
37. Silver nitrate, AgNO3, reacts with iron(III) chloride, FeCl3, to give silver chloride, AgCl, and iron(III) nitrate,
Fe(NO3)3. A solution containing 18.0 g of AgNO3 was mixed with a solution containing 32.4 g of FeCl3. How
many grams of which reactant remains after the reaction is over?
Percent Yield
38. Given the following equation:
H3PO4 + 3 KOH → K3PO4 + 3 H2O
If 49.0 g of H3PO4 is reacted with excess KOH, determine the percent yield of K3PO4 if you isolate 49.0 g of
K3PO4.
39. Given the following equation:
Al(OH)3 (s) + 3 HCl (aq) → AlCl3 (aq) + 3 H2O (l)
If you start with 50.3 g of Al(OH)3 and you isolate 39.5 g of AlCl3, what is the percent yield?
40. The Solvay process for the manufacture of sodium carbonate begins by passing ammonia and carbon
dioxide through a solution of sodium chloride to make sodium bicarbonate and ammonium chloride. The
equation for the overall reaction is
In the next step, sodium bicarbonate is heated to give sodium carbonate and two gases, carbon dioxide
and steam.
What is the theoretical yield of sodium carbonate, expressed in grams, if 120 g NaCl were used in the first
reaction? If 85.4 g of Na2CO3 were obtained, what was the percentage yield?