CH123 General Chemistry:
Dr. Jakubowski
Stoichiometry Questions I
9/19/01
Here are some typical stochiometry problems. You could ask many different
questions for each example given. One example is shown in red. (You could create
your own.)
Work on these before class next time.
1. Red phosphorus, P, reacts with liquid bromine, Br2, to produce phosphorous
tribromide. You reacted 12.7 g of Br2 with an excess of phosphorous, and isolated
10.9 g of the phosphorous tribromide. How much red phosphorous was present in
your isolated sample?
2. The souring of wine occurs when ethanol, C2H5OH(aq) reacts with O2 in the air to
produce acetic acid, CH3COOH(aq) and H2O. You seal 12.0 g of ethanol and 10.0 g
of oxygen in a bottle. How much ethanol remained unreacted?
3. Nicotine, the stimulant in tobacco, causes a very complex set of physiological
effects in the body. When a sample of mass 0.385 g was burned, 1.072 g of carbon
dioxide, 0.307 g of water, and 0.068 g of nitrogen were produced. What is the
empirical formula of nicotine?
4. Butane, C4H10, us used as a relatively cheap, portable heat source, using the
reaction shown below:
2C4H10(g) + 13O2(g) -------> 8CO2(g) + 10H2O(g)
A mixture of 4.66 g of butane and 11.1 L of oxygen (density 1.43g/L) was
combusted. Are there any reactants left over after the reaction? How much?
5. Hydrofluoric acid, HF, is never sold in glass bottles, because glass is composed of
calcium and sodium silicates that react with the HF. The reaction can be depicted,
for simplicity, as the interaction of silicon dioxide and the acid, as shown below in
the unbalanced equation. Assume the container is made of siilcion dioxide only.
SiO2(s) + HF(aq) ------> SiF4(g) + H2O(l)
A glass container contains 256 g of SiO2. HF was accidentally added to the
container. It was rinsed as soon as possible and dried, after which the container’s
mass was 249 g. Assuming all the HF added reacted, how much HF was added?
6. Oil paintings in which "white lead" has been used can be blackened by reaction with
H2S from air pollution or from glaze over the painting itself. The blackening comes
from the formation of lead sulfide, PbS. The PbS may be cleaned off by washing
with hydrogen peroxide, H2O2, which reacts with the lead sulfide to produce
PbSO4(s) and liquid water. 0.24 g of PbS must be removed from the painting.
How much hydrogen peroxide is required?
7. Methyl alcohol, CH3OH, is a clean-burning, easily handled fuel. It can be made as
the sole product of the direct reaction of CO and H2. (These reagents can be
obtained from reacting coal and water under the appropriate conditions.) You are
given 1.0 g of H2 and 74.5 g of CO. How much methyl alcohol can you make? How
much, if any, of each reagent, is remains after the reaction?
8. Vitamin C is a compound containing the elements C, H, and O. 4.00 g of solid
vitamin C is burned in excess oxygen to give 6.00 g of CO2 and 1.632 g of water.
What is the empirical formula of Vitamin C?
9. Potassium superoxide, KO2, is utilized in closed-system breathing apparatus, which
removes from exhaled air both carbon dioxide and water, and forms O2. Water
reacts with the potassium superoxide to form oxygen gas and potassium hydroxide.
The potassium hydroxide then reacts with carbon dioxide to form KHCO3(s). Write
balanced equations for these reactions.
10.Consider the following chemical reaction: (MW's are:CH3NHNH2 - 46.08; N2O4 92.01; N2 - 28.02; H2O - 18.02; CO2 - 44.01)
4CH3NHNH2(l) + 5N2O4(l) ----> 9N2(g) + 12H2O(g) + 4CO2(g)
You react 100 g CH3NHNH2 with 100 g N2O4. How many grams of N2 are
produced?
2