Stoichiometry Practice Problems Key

1. The Claus reactions, shown below, are used to generate elemental sulfur from hydrogen sulfide.

2H2S + 3O2  2SO2 + 2H2O SO2 + 2H2S  3S + 2H2O

How much sulfur (in grams) is produced from 15.0 g of O2?

a. 67.6 g b. 10.0 g c. 15.0 g d. 30.1 g e. none of these

2. When 189.4 g of ethylene (C2H4) burns in oxygen to give carbon dioxide and

water. How many grams of CO2 are formed?

a. 594.1 g b. 297.1 g c. 148.6 g d. 6.75 g e. 243.3 g

3. How many grams of Ca(NO3)2 can be produced by reacting excess HNO3 with 6.55 g of Ca(OH)2?

a. 7.25 g b. 14.5 g c. 29.0 g d. 13.1 g e. 6.55 g

4. When 20.0 g C2H6 and 60.0 g O2 react:

a. Write a balanced chemical equation.

2C2H6 + 7O2  4CO2 + 6H2O

b. How many grams of water are formed?

29.0 g

5. A 5.95 g sample of AgNO3 is reacted with BaCl2 to experimentally give 4.19 g of silver chloride. What is the percent yield of this product? a. 59.4% b. 70.4% c. 41.7% d. 83.5% e. 100%

6. The mineral mimetite has the formula Pb5(AsO4)3Cl. What mass % of oxygen does it contain?

a. 38.70% b. 16.34% c. 50.32% d. 12.90% e. 1.08%

7. A compound composed of sulfur and fluorine is found to contain 25.24% by mass of sulfur. If the molar mass of the compound is 254.11 g/mol, what is the molecular formula?

a. S3F8 b. S2F8

c. SF5 d. S2F5

e. S2F10

8. What is the molar mass of the compound formed between magnesium and phosphorous?

Mg3P2 = 134.87 g/mol

22 9. How many atoms of phosphorous are in 6.5 x 10 formula units of the compound in #8?

1.3 x 1023 atoms P