**Chapter 9**

**Homework 9.1 Molar Ratio Problems**

1. For each of the following chemical equations write all possible mole ratios.

e.g. for the equation 2 Al_{2}O_{3} ---> 4 Al + 3 O_{2}

the answer is 2 mol of Al_{2}O_{3 }for each 4 mol of Al_{
} 4 mol of Al for each 2 mol of Al_{2}O_{3
}2 mol of_{ }Al_{2}O_{3 }for each 3 mol of O_{2
}3 mol of O_{2} for each 2 mol of Al_{2}O_{3
}4 mol of Al for each 3 mol of O_{2}

3 mol of O_{2 }for each 4 mol of Al

a) 2 HgO ---> 2 Hg + O_{2}

b) 4 NH_{3} + 6 NO ---> 5 N_{2} + 6 H_{2}O

c) 2 Al + 3 H_{2}SO_{4} ---> Al_{2}(SO_{4})_{3}
+ 2 H_{2
}2. For each of the following chemical equations write all possible mole
ratios:_{
}a)_{ }2 Ca + O_{2} ---> 2 CaO

b) Mg + 2 HF ---> MgF_{2} + H_{2}

**Homework 9.2 Molar Mass Problems**

1. For the following equations determine to two decimal places the molar
masses of all substances involved:_{
}a)_{ }2 HgO ---> 2 Hg + O_{2
}b) 4 NH_{ }_{3} + 6 NO ---> 5 N_{2} + 6 H_{2}O

c) 2 Al + 3 H_{2}SO_{4} ---> Al_{2}(SO_{4})_{3}
+ 2 H_{2
}d) 2 Ca + O_{ }_{2} ---> 2 CaO

e) Na_{2}CO_{3} + Ca(OH)_{2} ---> 2 NaOH + CaCO_{3}

f) Mg + 2 HF ---> MgF_{2} + H_{2}

**Homework 9.3 Mole-Mole Problems**

1. How many moles of ammonia are produced when 6 mol of hydrogen gas react
with an excess of nitrogen gas according to the following balanced equation:

3 H_{2 }+ N_{2} ---> 2NH_{3}

(ans: 4 mol) (solution)

2. How many moles of potassium chlorate are needed to produce 15 mol of
oxygen according to the following balanced equation:_{
}2 KClO_{3 }---> 2 KCl + 3 O_{2}

(ans: 10. mol) (solution)

3. Given the following balanced equation:

4 NH_{3} + 3 O_{2} ---> 2 N_{2} + 6 H_{2}O

a) How many moles of oxygen will be need to react with 4 mol of NH_{3}?
(ans: 3 mol) (solution)

b) How many moles of N_{2} will be produced when 4 mole of NH_{3} react
with oxygen? (ans:
2 mol) (solution)

c) How many moles of water will be produced when 4 mole of NH_{3} react
with oxygen? (ans:
6 mol) (solution)

d) How many moles of NH_{3} will be needed to produce 4 mol of N_{2}?
(ans: 8 mol) (solution)

e) How many moles of oxygen will be needed to produce 4 mol of N_{2}?
(ans: 6 mol) (solution)

f) How many moles of water will be produced when 4 mol of N_{2} are
produced? (ans:
12 mol) (solution)

4. How many moles of oxygen are required to react with 4.50 mol of ethane,
C_{2}H_{6
}according to the following balanced equation:_{
}2 C_{2}H_{6 + }7 O_{2 }---> 4 CO_{2} +
6 H_{2}O

(ans: 15 mol) (solution)

**Homework 9.4 Mole-Mass / Mass-Mole Problems**

1. When magnesium burns in air, it combines with oxygen to form magnesium
oxide according to the following balanced equation:

2 Mg + O_{2} ---> 2 MgO

What mass of magnesium oxide is produced from 2.00 mol of magnesium? (ans:
80.6 g) (solution)

2. What mass in grams of oxygen combines with 2.00 mol of magnesium according
to the above reaction?

(ans: 32.0 g) (solution)

3. What mass of glucose can be produced from a photosynthesis reaction that
occurs using 10 mol of CO_{2} according to the following balanced equation:

6 CO_{2} + 6 H_{2}O ----> C_{6}H_{12}O_{6} +
6 O_{2}

(ans: 30.3 g) (solution)

4. Sodium chloride is produced from its elements according to the following
balanced equation:

2 Na + Cl_{2} ---> 2 NaCl

a)What mass of sodium would be required to produce 25.0 mol of sodium chloride?
(ans: 574.8 g) (solution)

b) What mass of chlorine would be required to produce 25.0 mol of sodium chloride?
(ans: 886.3 g) (solution)

5. How many moles of mercury (II) oxide, HgO, are needed to produce 125 g of
oxygen according to the following balanced equation:

2 HgO ---> 2 Hg + O_{2}

(ans: 7.81 mol) (solution)

6. How many moles of mercury are produced when 125 g of oxygen are produced
according to the equation above? (ans: 7.81 mol) (solution)

7. What mass of HCl is consumed by the reaction of 2.50 mol of magnesium according
to the following balanced equation:_{
}Mg + 2 HCl ---> MgCl_{2} + H_{2}

(ans: 182 g) (solution)

8. How many moles of water are needed to react with 32.0 g of calcium
carbide to produce acetylene, C_{2}H_{2}, according to the
following balanced equation:_{
}CaC_{2} + 2 H_{2}O ---> C_{2}H_{2} +
Ca(OH)_{2}

(ans: 0.998 mol) (solution)

**Homework 9.5 Mass-Mass Problems**

1. How many grams of ammonium nitrate are required to produce 33.0 g of N_{2}O,
nitrous oxide or laughing gas, according to the following balanced equation:

NH_{4}NO_{3} ---> N_{2}O + 2 H_{2}O

(ans: 60.0 g) (solution)

2. How many grams of water are produced when 33.0 g of nitrous oxide are produced
according to the above reaction? (ans: 27.0 g) (solution)

3. What mass of silver is produced from 100 g of copper according to the following
balanced equation:

Cu + 2 AgNO_{3} ---> Cu(NO_{3})_{2} + 2 Ag

(ans: 340. g) (solution)

4. What mass of aluminum is produced by the decomposition of 50 g of aluminum
oxide according to the following balanced equation:

2 Al_{2}O_{3} ---> 4 Al + 3 O_{2
}(ans: 26.46 g) (solution)

5. What mass of AgCl is produced from 75.0 g of AgNO_{3} according
to the following balanced equation:

NaCl + AgNO_{3} ---> NaNO_{3} + AgCl

(ans: 63.3 g) (solution)

6. How many grams of carbon dioxide are produced when 250 g of acetylene, C_{2}H_{2},
react with oxygen according to the following balanced equation:

2 C_{2}H_{2} + 5 O_{2} ---> 4 CO_{2} + 2H_{2}O

(ans: 845 g) (solution)

**Homework 9.6 Limiting Reactant Problems**

1. Which is the limiting reactant when 0.750 mol of N_{2}H_{4},
hydrazine, reacts with 0.50 mol of hydrogen peroxide according to the following
balanced equation:

N_{2}H_{4} + H_{2}O_{2} ---> N_{2} +
4 H_{2}O

(solution) (alternate
solution)

2. If 20.5 g of chlorine is reacted with 20.5 g of sodium which reactant is
in excess and which is the limiting reactant according to the following balanced
equation:

2 Na + Cl_{2} ---> 2 NaCl

(solution)

3. If 2.00 mol of Zn are heated with 1.00 mol of sulfur, identify the limiting
reactant for the following balanced equation:

8 Zn + S_{8} ---> 8 ZnS

(solution)

4. a) If 2.40 mol of carbon are exposed to 3.10 mol of steam, identify the
limiting reactant in the following balanced equation:

C + H_{2}O ---> H_{2} + CO

(solution)

b) How many moles of excess reactant remain? (solution)

**Homework 9.7 Percent Yield Problems**

1. If 75.0 g of CO reacts to produce 68.4 g CH_{3}OH,
methanol, what is the percent yield of methanol according to the following balanced
equation:

CO + 2 H_{2} ---> CH_{3}OH

(solution)

2. When 200 g of calcium carbonate are heated the actual yield of calcium
oxide is 105 g. What is the percent yield if the the following is the balanced
equation:

CaCO_{3} ---> CaO + CO_{2
}

(solution)