General Chemistry I

Writing & Balancing Chem. Equations, Plus Conversions

Answers to Practice Problems

1.  For the following, give the correctly balanced chemical equation for:

 

a. the reaction of silver acetate with magnesium chloride to produce magnesium acetate and silver chloride.           

                            2 AgC2H3O2  +  MgCl2  ¾¾®  2 AgCl  +  Mg(C2H3O2)2

 

 

b. the reaction of calcium oxide with tetraphosphorus decoxide to produce calcium phosphate.

                            6 CaO  +   P4O10  ¾¾®  2 Ca3(PO4)2

 

 

c.  the reaction of aluminum sulfate with sodium hydroxide to produce aluminum hydroxide and sodium sulfate.

                             Al2(SO4)3  +  6 NaOH  ¾¾®  2 Al(OH)3  +  3 Na2SO4

 

 

d.  the reaction of calcium hydroxide and hydrochloric acid to produce calcium chloride and water.

                             Ca(OH)2  +  2 HCl  ¾¾®  CaCl2  +  2 H2O

 

 

e.  the complete combustion of C7H6O2.

                            2  C7H6O2  +  15 O2  ¾¾®  14  CO2  +  6  H2O

 

 

f.  the reaction of nitrogen dioxide with water to produce nitric acid and nitrogen monoxide.

                            3 NO2  +  H2O  ¾¾®  2 HNO3  +  NO

 

 

g. the complete combustion of butane, C4H10.

                             2 C4H10  +  13 O2  ¾¾®  8 CO2  +  10 H2O

 

 

h.  the reaction of nitric acid with calcium hydroxide to produce calcium nitrate and water.

                             2 HNO3  +  Ca(OH)2  ¾¾®  Ca(NO3)2  +  2 H2O

 

2.  How many moles of nickel(II) hydroxide are produced from the complete reaction of 2.5 moles of nickel(II) chloride with excess sodium hydroxide?  (Sodium chloride is the other product.)                                   

Moles NiCl2  ¾®  Moles Ni(OH)2

2.5 moles nickel(II) hydroxide

3.  How many grams of nickel(II) hydroxide are produced from the reaction of 18.6 g of nickel(II) chloride with excess sodium hydroxide?  (Same chemical equation as above.)

Grams NiCl2  ¾®  Moles NiCl2  ¾®  Moles Ni(OH)2  ¾®  Grams Ni(OH)2

13.3 grams nickel(II) hydroxide

4. Use the following balanced chemical equation to answer the questions below.

 

2 HNO3  +  Ca(OH)2  ¾¾®  Ca(NO3)2  +  2 H2O

 

 

 

a.  What mass, in grams, of calcium hydroxide is required to react completely with 24.7 g of HNO3?

Grams HNO3  ¾®  Moles HNO3  ¾®  Moles Ca(OH)2  ¾®  Grams Ca(OH)2

14.5 grams calcium hydroxide

 

 

b.  What mass, in grams, of calcium nitrate forms from the complete reaction of 35.0 g of HNO3 with excess calcium hydroxide?

Grams HNO3  ¾®  Moles HNO3  ¾®  Moles Ca(NO3)2  ¾®  Grams Ca(NO3)2

45.6 grams calcium nitrate

 

 

c.  What is the percent yield of calcium nitrate if the reaction of 43.5 g nitric acid with 28.3g of calcium hydroxide yields 48.2 g of calcium nitrate?

Grams HNO3  ¾®  Moles HNO3  ¾®  Moles Ca(NO3)2  ¾®  Grams Ca(NO3)2

Grams Ca(OH)2  ¾®  Moles Ca(OH)2  ¾®  Moles Ca(NO3)2  ¾®  Grams Ca(NO3)2

Nitric acid is limiting reagent, theoretical yield is 56.6 g,

Percent yield = actual yield ÷ theoretical yield X 100 = 85.2%

 

5. Use the following balanced chemical equation to answer the questions below.

 

3 Mg  +  B2O3  ¾¾®  2 B  +  3 MgO

 

 

 

a. How many grams of magnesium are required to produce 11.4 g of boron?    

Grams B  ¾® Moles B ¾®  Moles Mg  ¾®  Grams Mg

38.5 g magnesium

 

b. What mass, in grams, of B2O3 is required to completely react with 124.4 g of magnesium?  

Grams Mg  ¾®  Moles Mg  ¾®  Moles B2O3  ¾®  Grams B2O3

118.8 grams B2O3

 

c. How many grams of boron are produced from the complete reaction of 87.3 g of magnesium with excess B2O3?

Grams Mg  ¾®  Moles Mg  ¾®  Moles B  ¾®  Grams B

25.9 grams boron

 

d. What is the maximum amount of boron that can be produced from the reaction of 9.13 g of magnesium with 7.95 g B2O3?     

Grams Mg  ¾®  Moles Mg  ¾®  Moles B  ¾®  Grams B

Grams B2O3  ¾®  Moles B2O3  ¾®  Moles B ¾®  Grams B

2.47 grams boron (This is also theoretical yield.)

 

e. The complete reaction of 14.3 g of magnesium with 13.1 g B2O3 produces 19.8 g of magnesium oxide.  What are the limiting reactant, theoretical yield, and percent yield?

Grams Mg  ¾®  Moles Mg  ¾®  Moles MgO  ¾®  Grams MgO

Grams B2O3  ¾®  Moles B2O3  ¾®  Moles MgO  ¾®  Grams MgO

B2O3 is limiting reagent, theoretical yield is 22.8 g,  percent yield is 86.8%

6.  Propane, C3H8, is combusted completely.

 

a. Write and balance the chemical equation for this reaction.

                             C3H8  +  5  O2  ¾¾®  3  CO2  +  4  H2O

 

b. How many molecules of propane are required to produce 25.8 g carbon dioxide in the presence of excess oxygen?

Grams CO2  ¾®  Moles CO2 ¾®  Moles C3H8  ¾®  Molecules C3H8

1.18 x 1023 propane molecules

 

c. How many moles of oxygen are required to completely react with 94.7 g propane?                   

Grams C3H8  ¾®  Moles C3H8  ¾®  Moles O2

10.7 moles oxygen

 

d. What is the maximum amount, in grams, of water that can be formed from the complete reaction of 8.04 x 10-2 g propane with 9.83 x 10-2 g oxygen?    

Grams C3H8  ¾®  Moles C3H8 ¾®  Moles H2O  ¾®  Grams H2O

Grams O2 ¾®  Moles O2  ¾®  Moles H2O  ¾®  Grams H2O

0.0442 grams water

 

e. The complete reaction of 49.7 g oxygen with 14.6 g propane produces 38.0 g carbon dioxide.  What are the limiting reagent, theoretical yield, and percent yield for this reaction?        

Grams O2  ¾®  Moles O2  ¾®  Moles CO2 ¾®  Grams CO2

Grams C3H8  ¾®  Moles C3H8  ¾®  Moles CO2  ¾®  Grams CO2

oxygen is limiting reagent,  theoretical yield is 41.0 g,  percent yield is 92.7%

7.  Calculate the molarity of a solution that contains 7.5 x 10-2 mole sodium sulfate in a total of 250.0 mL of solution.                  0.30 M

8.  Calculate the molarity of a solution made by dissolving 25.0 g sodium chloride in a total of 500.0 mL of water.                          0.855 M

9. A solution is prepared by dissolving 84.0 g potassium phosphate in a total of 1.5 L of solution.  The density of the solution is 1.23 g/mL.

 

a. Calculate the molarity of the solution.                 0.264 M

 

b. Calculate the percent by mass of the solution.     4.55%  

10. Calculate the percent by mass of a solution prepared by dissolving 1.8 x 10-3 mole of magnesium chloride in 200.0 mL of aqueous solution.  The solution density is 1.02 g/mL.         0.084%

11. What mass, in grams, of calcium chloride is required to prepare 750.0 mL of a 5.0% solution?  The solution density is 1.18 g/mL.       44 grams calcium chloride

12.  How many grams of copper(II) sulfate are required to prepare 1.5 L of a 1.2 M solution?              2.9 x 102 grams copper(II) sulfate

13.  How many mL of ethyl alcohol (C2H5OH,  D = 0.789 g/mL) are required to prepare 500.0 mL of a 1.2 M solution of ethyl alcohol?       35 mL

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