Stoichiometry Problems 1

1.  When lead (II) sulfide is burned in air, lead (II) oxide and sulfur dioxide are produced.  If 0.890
moles of sulfur dioxide were produced, how many moles of oxygen gas were required to react with
the lead (II) sulfide?                                 ___ PbS  +  ___ O2
à  ___ PbO  +  ___ SO2

2.  In the synthesis reaction of aluminum and oxygen to produce aluminum oxide, how many grams of
aluminum are required to react with 0.223 moles of oxygen?
___ Al  +  ___ O2
à  ___ Al2O3

3.  Calculate the number of grams of oxygen produced if 2.50 grams of potassium chlorate are
decomposed completely by heating.
___ KClO3
à  ___ KCl  +  ___ O2

4.  How many moles of oxygen are needed for the complete combustion of 3.0 moles of methane
(CH4)?                                  ___ CH4  +  ___ O2
à  ___ CO2  +  ___ H2O

5.  Using the same equation from #4, how many grams of carbon dioxide are formed when 8.0 grams
of methane react?                  ___ CH4  +  ___ O2
à  ___ CO2  +  ___ H2O

6.  When elemental sulfur combines with oxygen gas, sulfur dioxide is formed.  What is the total
number of grams of oxygen needed to react completely with 2.0 moles of sulfur?
___ S  +  ___ O2
à  ___ SO2

7.  In the synthesis of water from its elements, what is the total number of grams of oxygen gas
needed to produce 54 grams of water?          ___ H2  +  ___ O2
à  ___ H2O

8.  How many moles of aluminum oxide will be formed when 27 grams of aluminum react completely
with excess oxygen gas?                                       ___ Al  +  ___ O2
à  ___ Al2O3

9. What mass (in grams) of sodium oxide is produced by the reaction of 1.44 grams of sodium with
excess oxygen?                                           __ Na +   __ O2
à     __ Na2O

10. What mass (in grams) of water will be given off when 1.92 x 1022 molecules of octane (C8H18) are
burned completely in air?                             __ C8H18 +     __ O2
à      __ CO2 +     __ H2O

11. How many grams of Al2(SO4)3 are need to react with KCl in order to produce 1.245 moles of K2SO4?
__ Al2(SO4)3  +     __ KCl
à      __ AlCl3  +    __ K2SO4

12. Hydrogen gas can be produced through the following unbalanced reaction.
__ Mg  +    __ HCl
à     __ MgCl2  +    __ H2

a. What mass of HCl is consumed by the reaction of 2.50 moles of magnesium?

b. What mass of each product is produced in part a.?

13. Acetylene gas, C2H2, used in welding, produces an extremely hot flame when it burns in pure
oxygen according to the following unbalanced reaction.
__ C2H2 +    __ O2
à    __ CO2 +    __ H2O
How many molecules of CO2 are produced when 2.50 x 104 grams of C2H2 burn completely?

1.)  1.34 moles O2          2.)  8.02 g Al                 3.)  0.980 g O2               4.)  6.0 moles O2            5.)  22 g CO2
6.)  64 g O2                    7.) 48 g O2                     8.)  0.50 moles Al2O3                  9.)  1.94 g Na2O
10.)  5.16 g H2O 11.)  142.1 g Al2(SO4)3                12.)  a)  183 g HCl         b)  238 g MgCl2; 5.00 g H2
13.)  1.16 x 1027 mcs CO2

PERCENT YIELD

1.)  Use the following information to answer the questions.  In the following reaction, 41.0
grams of lead (II) chloride are reacted with excess sodium chromate.

___ PbCl2  +  ___ Na2CrO4  à  ___ PbCrO4  +  ___ NaCl

(A)  How many moles of lead (II) chromate will be produced?

(B)  What is the theoretical yield (in grams) of sodium chloride in this reaction?

(C)  If a student performed this experiment and recovered 16.5 grams of sodium
chloride, what is the student’s percent yield?

2.)  Use the following information to answer the questions.  In the following reaction, 1.70
moles of zinc nitrate are reacted with excess chromium (II) phosphide.

___ Zn(NO3)2  +  ___ Cr3P2  à  ___ Zn3P2  +  ___ Cr(NO3)2

(A)  What is the theoretical yield (in grams) of zinc phosphide?

(B)  If a student performed this experiment and recovered 149 grams of zinc
phosphide, what is the student’s percent yield?

3.)  Use the following information to answer the questions.  In the following reaction, 10.0
grams of copper (II) sulfate are reacted with excess iron (III) phosphate.

___ CuSO4  +  ___ FePO4  à  ___ Cu3(PO4)2  +  ___ Fe2(SO4)3

(A)  How many grams of copper (II) phosphate can be produced?

(B)  If a student performed this experiment and recovered 6.70 grams of copper (II)
phosphate, what is the student’s percent yield?

Answers:           1.)        (A) 0.147 moles             (B) 17.2 g                      (C) 95.9 %
2.)        (A) 146 g                       (B) 102 %
3.)        (A) 7.95 g                      (B) 84.3 %

UNIT 9 TEST REVIEW

1.) A reaction between methane and sulfur produces carbon disulfide (CS2), a liquid often used in the production of cellophane.

___ CH4  +  ___ S8  à  ___ CS2  +  ___ H2S

If 1.50 moles of S8 are used, (A) how many moles of CS2 are produced?  (B) How many moles of H2S are produced?

2.) Lead (II) oxide is obtained by roasting galena, lead (II) sulfide, in air.

___ PbS  +  ___ O2  à  ___ PbO  +  ___ SO2

(A) Determine the theoretical yield (in grams) of PbO if 200.0 grams of PbS are heated.

(B) What is the percent yield if 170.0 grams of PbO are obtained?

3.) Some rockets are fueled by the reaction of hydrazine (N2H2) and hydrogen peroxide (H2O2).  How many moles of nitrogen gas can be produced by reacting 255 grams of hydrazine with excess hydrogen peroxide?

___ N2H2  +  ___ H2O2  à  ___ N2  +  ___ H2O

4.) One in a series of reactions that inflate automobile air bags is the decomposition of sodium azide (NaN3).

_  NaN3  à   _  Na  +   _  N2

Determine the mass of N2 produced if 100.0 grams of NaN3 are decomposed.

5.) Titanium is a transition metal used in many alloys because it is extremely strong and lightweight.  Titanium tetrachloride (TiCl4) is extracted from titanium oxide using chlorine and carbon.

TiO2  +  C  +   _  Cl2  à  TiCl4  +  CO2

If you begin with 1.25 moles of TiO2, what mass of Cl2 gas is needed?

6.) How many molecules of iodine can be produced by the complete reaction of 43.97 grams of KI?

___ CuCl2  +  ___ KI  à  ___ CuI  +  ___ KCl  +  ___ I2

7.) What mass of ammonia (NH3) is needed to react completely with oxygen to produce 3.54 x 1024 molecules of water?

___ NH3  +  ___ O2  à  ___ NO  +  ___ H2O

ANSWERS:  1.) (A) 3.00 moles CS2   (B) 6.00 moles H2S                  2.) (A) 186.6 g PbO   (B) 91.10 %

3.) 8.50 moles N2           4.) 64.60 g N2                5.) 178 g Cl2           6.) 3.988 x 1022 mcs I2                        7.) 66.6 g NH3