# Balancing Reactions and Stoichiometry Problem Set

This problem set was developed by S.E. Van Bramer for Chemistry 145 at Widener University. Problems adapted from Zumdahl, Chemistry, Saunders (1993) p121. (DOUBLE CHECK)

1. Balance the following reactions:
1. Fe2O3 + CO -> Fe3O4 + CO2
2. Fe3O4 + CO -> FeO + CO2
3. C12H22O11(s) + O2(g) -> CO2(g) + H2O
4. Fe(s) + O2(g) -> Fe2O3
5. Ca(s) + H2O(l) -> Ca(OH)2(aq) + H2(g)

2. Over the years, the thermite reaction has been used for welding railroad rails, in incendiary bombs, and to ignite solid-fuel rocket motors. The reaction is:

Fe2O3(s) + 2Al(s) -> 2Fe(l) + Al2O3(s)

What masses of iron(III) oxide and aluminum must be used to produce 15.0 g iron? What is the maximum mass of aluminum oxide that could be produced? How much aluminum oxide would be produced if the yield is 93%?

3. Elixirs such as Alka-Seltzer use the reaction of sodium bicarbonate with citric acid in aqueous solution to produce a fizz. Balance the following reaction. What mass of C6H8O7 should be used for every 1.0*102 mg of NaHCO3? What mass of CO2(g) could be produced by this mixture?

4. A confiscated white substance, suspected of being cocaine, was purified by a forensic chemist and subjected to elemental analysis. Combustion of a 50.86-mg sample yielded 150.0 mg CO2 and 46.05 mg H2O. Analysis for nitrogen showed that the compound contained 9.39% N by mass. The formula of cocaine is C17H21NO4. Can the forensic chemist conclude that the suspected compound is cocaine?

Please send comments or suggestions to svanbram@science.widener.edu

Scott Van Bramer
Department of Chemistry
Widener University
Chester, PA 19013