Unit 8 Review Stoichiometry

1
Unit 8 ReviewStoichiometry
2
1. Describe how a chemist uses stoichiometry?

• To determine the amount of reactants needed or
  products formed based on the amount of another
  reactant or product.

3
How many grams of sodium nitrate are formed if
20.0 g of Na3N are reacted with excess silver
nitrate? Na3N (aq) 3 AgNO3 (aq)
? Ag3N (s) 3 NaNO3 (aq)
4
What mass of ammonia, NH3, is necessary to react
with 2.15 x 1024 molecules of oxygen in the
following equation? ____ NH3(g) ____ O2(g) ?
____ H2O(g) ____NO2(g)
5
5. What is a limiting reactant? How does a LR
affect a reaction? What do you call the
left-over chemicals?

• Limiting reactant is the reactant that is used up
  first.
• LR being used up stops the reaction and
  determines how much product can form.
• Left-over chemicals are called Excess Reactants
  (ER).

6
6. If 75.00 grams of zinc metal and 100.0 grams
of copper (I) nitrate react, how many grams of
copper metal will be produced according to the
following equation? What is the limiting
reactant? Zn (s) 2 CuNO3 (aq) ? 2 Cu
(s) Zn(NO3)2 (aq)
7
Accelerated Only How many grams of excess
reactant are left over?
8
Use the reaction to determine the limiting
reactant in the following scenarios?O2 2
NO ? 2 NO27. 4 molecules O2 reacts with 6
molecules NO ___________8. 1 mole O2 reacts
with 3 moles NO ___________9. 5 moles O2
reacts with 7.00 moles NO ___________10.
30.0 g O2 reacts with 30.0 g NO
___________
NO
O2
NO
NO
9
What is percent yield? What does it tell you
about a reaction? What is the equation for
percent yield?

• Ratio of grams actually formed to grams that
  should have formed.
• Describes the efficiency of a reaction.

10
12. How does the actual yield of a chemical
reaction compare to the theoretical yield? Why?

• The actual yield of a reaction is measured in a
  lab and theoretical yield is calculated. They
  are different because of lab errors,
  contamination, inefficient reactions, etc

11
Burning 20.0 grams of magnesium metal produces
32.5 grams of solid product. What is the percent
yield for this reaction? ____ Mg (s)
____ O2 (g) ? ____ MgO (s)
12
14. 10.0 grams of iron (II) sulfide is reacted
according to the following equation. The percent
yield is 97.25. How many grams of rust (Fe2O3)
are actually formed? ____ FeS (s) ____ O2
(g) ? ____ Fe2O3 (s) ____ SO2 (g)
13
15. A student carried out this experiment in the
lab by reacting 22.4 g of oxygen with excess
hydrogen and 24.5 g of water were formed. What
is the percent yield
14
3.74 g of copper is formed when 1.87 g of
aluminum reacts with excess of copper (II)
sulfate. 2Al (s) 3 CuSO4 (aq) ?
Al2(SO4)3 (aq) 3Cu (s)

• calculate the theoretical yield
• calculate the percent yield
• calculate the experimental error.