Stoichiometry Problems
1. Disulfide dichloride, S2Cl2, is used in the vulcanization of rubber, a process that prevents the
slippage of rubber molecules past one another when stretched. It is prepared by heating sulfur
in an atmosphere of chlorine:
S8(s) + 4Cl2(g)
4S2Cl2(l)
a. What is the theoretical yield of S2Cl2 in grams when 4.06 grams of Se are heated with
6.24 grams of Cl2? If the actual yield of S2Cl2 is 6.55 grams.
b. What is the percent yield?
2. When tin comes in contact with the oxygen in the air, tin (IV) oxide, SnO2, is formed.
Sn(s) + O2(g)
SnO2(s)
A piece of tin foil, 8.25cm x 21.5cm x 0.600mm (d=7.28g/cm 3) is exposed to oxygen.
a. Assuming that all the tin has reacted, what is the mass of the oxidized tin foil? Air is
about 21% oxygen by volume (d=1.309g/L at 25C and 1 atm).
b. How many liters of air are required to completely react with the tin foil?
3. Oxygen masks for producing O2 in emergency situations contain potassium superoxide, KO2. It
reacts with CO2 and H2O in exhaled air to produce oxygen:
4KO2(s) + 2H2O(g) + 4CO2(g)
4KHCO3(s) + 3O2(g)
If a person wearing such a mask exhales 0.702 grams CO2/min, how many grams of KO2 are
consumed in 25 minutes?
4. When iron and steam react at high temperatures, the following reaction takes place:
3Fe(s) + 4H2O(g)
Fe3O4(s) + 4H2(g)
How much iron must react with the excess steam to form 897 grams of Fe3O4 if the reaction
yield is 69%.
5. Oxyacetylene torches used in welding reach temperatures near 2000C. The reaction involved in
the combustion of acetylene is:
2C2H2(g) + 5O2(g)
4CO2(g) + 2H2O(g)
a. Starting with 175 grams of both acetylene and oxygen, what is the theoretical yield, in
grams of carbon dioxide?
b. If 68.5L (d=1.85g/L) of carbon dioxide is produced, what is the percent yield at the same
conditions of temperature and pressure?
6. The Space Shuttle uses aluminum metal and ammonium perchlorate in its reusable booster
rockets. The products of the reaction are aluminum oxide, aluminum chloride, nitrogen
monoxide gas, and steam. The reaction contains 7.00 grams of aluminum and 9.32 grams of
ammonium perchlorate.
a. Write the balanced equation for the reaction.
b. What is the theoretical yield of aluminum oxide?
c. If 1.56 grams of aluminum oxide is formed, what is the percent yield?
d. How many grams of excess reactant are unused?
7. Aspirin, C9H8O4, is prepared by reacting salicylic acid, C7H6O3, with acetic anhydride,C4H6O3, in
the reaction:
C7H6O3 + C4H6O3
C9H8O4 + C2H4O2(l)
A student is told to prepare 45.0 grams of aspirin. She is also told to use a 55.0% excess of acetic
anhydride and to expect to get an 85.0% yield in the reaction. How many grams of each reactant
should she use?
8. A student prepares phosphorus acid, H3PO3, by reacting solid phosphorus triiodide with water.
PI3(s) + 3H2O(l)
H3PO3(s) + 3HI(g)
The student needs to obtain 0.250L of H3PO3 (d=1.651 g/cm3). The procedure calls for 45.0%
excess of water and a yield of 75.0%. How much phosphorus triiodide should be weighed out?
What volume of water (d=1.00 g/cm3) should be used?