Chapter 12 : Stoichiometry
Definition:
a branch of chemistry that deals with the application of the laws of
definite proportions and of the conservation of mass and energy to
chemical activity
the quantitative relationship between constituents in a chemical
substance
the quantitative relationship between two or more substances especially
in processes involving physical or chemical change
1 cup M&M Candies
2 cups All-Purpose Flour
1/2 tsp. Baking Soda
1/2 tsp. Baking Powder
1 1/4 cups Sugar
Layer the ingredients in the order given into a
wide-mouth 1-quart canning jar.
Pack each layer in place before adding the next
ingredients.
To Make Cookies Add:
1 Jar M&M Cookie Mix
3/4 cup Butter or Margarine, Softened
2 Eggs, Slightly Beaten
1 tsp. Vanilla
Preheat the oven to 375 degrees.
In a large bowl, cream the butter, eggs, and
vanilla.
Add the M&M Cookie Mix and
Stir until the mixture is well blended.
Drop by rounded tablespoonfuls onto greased
cookie sheet.
Bake for 10-12 minutes.
Cool on a wire rack.
Yield: 3 dozen cookies
Here's the Recipe:
1 cup M&M Candies
2 cups All-Purpose Flour
1/2 tsp. Baking Soda
1/2 tsp. Baking Powder
1 1/4 cups Sugar
Yield: 3 dozen cookies
The reaction between nitrogen and oxygen to produce nitrogen
dioxide:
N2(g) + O2(g)---> NO2(g)
N2(g) + 3 H2(g)---> 2 NH3(g)
N2(g) + 3 H2(g)---> 2 NH3(g)
How many moles of
ammonia gas can be created
from 5 moles of nitrogen
gas?
How many moles of
nitrogen gas are needed
to react with 12 moles of
hydrogen gas?
How many moles of ammonia
can be created from 11.7
moles of hydrogen?
2 C(s) + O2(g) -----> 2 CO(g)
Law of Conservation of Mass
Mass of all reactants added together must equal the
mass of all products added together.
2 C(s) + O2(g) -----> 2 CO(g)
Using mol ratios to calculate mass
How many grams of nitrogen dioxide will be produced if 4
mol of nitrogen gas are reacted with excess oxygen?
N2(g) + 2 O2(g)---> 2 NO2(g)
What mass of oxygen gas was used to produce 13 mol of
nitrogen dioxide?
N2(g) + 2 O2(g)---> 2 NO2(g)
Using mass and mol ratios to calculate mass
If 134.7 g of nitrogen gas is reacted with excess oxygen, how
many grams of nitrogen dioxide will be formed?
N2(g) + 2 O2(g)---> 2 NO2(g)
If 350.6 g of nitrogen dioxide are formed, how many grams of
oxygen gas were reacted?
N2(g) + 2 O2(g)---> 2 NO2(g)
Bonus:
Dry air is about 20.95% oxygen by volume. How many
oxygen molecules are in a 75.0g sample of air? The
density of air is 1.19 g/L.
Al(s) + H2SO4(aq) →
If 28.83 g of Aluminum is completely reacted, how many
grams of Hydrogen sulfate (hydrochloric acid) are
needed?
Other Stoichiometric Calculations
According to the following reaction, how much ammonium
chloride could be made from 593 mL of hydrochloric acid?
NH3 + HCl  NH4Cl
Density:
Hydrochloric acid = 1.20 g/mL
How many mL of chlorine gas would be needed to produce 35.9 g of sodium chloride?
2Na (s) + Cl2 (g)  2NaCl (s)
For each of the reactions listed, determine the
mole ratio of reactants that
produces the maximum amount of precipitate.
Be sure to balance the
equations.
a. AgNO3(aq) NaCl(aq) AgCl(s) NaNO3(aq)
b. Cu NO3 2(aq) K2CO3(aq) CuCO3(s)
KNO3(aq)
c. ZnCl2(aq) NaOH(aq) Zn(OH)2(s) NaCl(aq)
d. CaCl2(aq) Na2C2O4(aq) CaC2O4(s)
NaCl(aq)
Limiting Reactant
If 13 mol of sodium react with 7 mol of chlorine, which
reactant will be completely used up? Which will not?
2Na + Cl2  2NaCl
If 4 mol of aluminum hydroxide are reacted with 11 mol of
hydrochloric acid, which will be completely used up? Which
will not?
Al(OH)3 + 3HCl  AlCl3 + 3H2O
If 217.3 mol of oxygen gas are combined with 415.7 mol of
magnesium metal, which is the limiting reactant?
2Mg + O2  2MgO
45.9 g of sodium metal are combined with 74.3 g of
chlorine gas. Which is the limiting reactant?
2Na + Cl2  2NaCl
117.3 g of aluminum hydroxide is combined with 450.0 g of
hydrochloric acid. Which is the limiting reactant?
Al(OH)3 + 3HCl  AlCl3 + 3H2O
94.0 g of magnesium metal are combined with 113.0 g of
oxygen gas. What is the maximum amount of magnesium
oxide that could form?
2Mg + O2  2MgO
STOICHIOMETRY LAB
PROCEDURE:
1. Measure the mass of the aluminum foil provided. Tear into small pieces, do not fold or
crush the aluminum foil
or it will negatively affect your reaction.
2. Mass out approximately 4.0 grams of copper (II) sulfate and mix with 50 ml of distilled
water and a pinch of
salt in beaker (make sure to record the exact mass you have). Add the aluminum after the
CuSO4 has dissolved.
3. Place the beaker over a Bunsen burner, and begin to heat. Use a stirring rod to regularly stir
the mixture. If and
when the solution begins to boil turn off the flame. During this time the aluminum will
dissolve, and the copper
begins to precipitate.
4. When all of the aluminum has dissolved or the solution becomes clear allow the mixture to
sit for about five
minutes and cool, periodically stirring the mixture.
5. Mark a piece of filter paper with your initials. Mass the filter paper.
6. Filter the copper out of solution using your filter paper, a funnel, and an empty beaker.
7. Wash the copper by running distilled water through the funnel with the copper and filter
paper.
8. Allow the water to drain, and store your copper in the designated drying oven.
9. The following class period, mass your copper and filter paper.
Trial 1:
1. Determine the theoretical yield of copper based on the
amounts of reactants you used. (you will perform the calculation
twice, once for each reactant).
2. What was the actual yield of copper?
3. Which was the limiting reactant? Please explain your answer.
4. Determine the percent yield. (p. 372)
Trial 2:
Repeat procedure above.
Al (in grams)
CuSO4 (in grams)
Cu produced (in grams)
% Yield
Al (in grams)
CuSO4 (in grams)
Cu produced (in grams) % Yield
Al (in grams)
CuSO4 (in grams)
Cu produced (in grams) % Yield
Percent Yield
65.0 g of sodium metal is reacted with excess chlorine gas.
If 107 grams of sodium chloride were produced, what is
the percent yield of this reaction?
2Na + Cl2  2NaCl
If 140.0 g of hydrochloric acid is combined with excess aluminum
hydroxide and 57.5 g of water are formed, what is the percent
yield of this reaction?
Al(OH)3 + 3HCl  AlCl3 + 3H2O
4800 g of magnesium metal are reacted with 1300 L of oxygen gas.
If 6300 g of magnesium oxide are formed, what is the percent yield
of this reaction?
2Mg + O2  2MgO
In the following reaction, 1270 g of ammonia are combined with
935 mL of hydrochloric acid to form 235 mL of ammonium chloride.
What is the percent yield for this reaction?
NH3 + HCl  NH4Cl