Chemistry Unit 8 Worksheet 4
Samples of Every Kind of Problem
On a separate sheet of paper, write a complete solution to each of the problems below.
Follow the procedure outlined in class. Be sure to circle your final answer.
1. Calculate the number of moles of potassium chlorate, KClO3 (s), that must decompose
to produce potassium chloride, KCl (s), and 1.8 moles of oxygen gas.
Equation:
2 KClO3 
Before:
1.2
0
Change:
-1.2
+1.2
+1.8
0
1.2
1.8
After:
2 KCl
+
3 O2
1.2 moles
KClO3 needed
0
2. In a single displacement reaction, magnesium metal reacts with hydrochloric acid to
produce magnesium chloride and hydrogen gas. How many moles of hydrochloric acid
are needed to completely react with 2.43 g of magnesium?
Equation:
Mg +
Before:
0.100
Change:
-0.100
After:
 MgCl2 + H2
2 HCl
?
-0.200 +
0
?
0
0
0.100 +
0.100
0.100
0.100
0.200 moles
HCl needed
3. Ethane, C2H6 reacts with oxygen gas to produce carbon dioxide gas and water vapor.
What mass of oxygen gas is required to react with 2.20 moles of ethane?
2 C 2H 6
Before:
2.20
xs
0
Change:
-2.20
- 7.70
+ 4.40
+ 6.60
0
xs
4.40
6.60
After:
+

Equation:
7 O2
O2 needed: 7.70 mole x 32.0 g
1 mole
4 CO2
+ 6 H 2O
0
= 246 g O2 required
4. Determine the mass of sodium nitrate produced when 0.73 g of nickel (II) nitrate
reacts with sodium hydroxide according to the following equation:
Ni(NO3)2 + 2 NaOH --> Ni(OH)2 + 2 NaNO3
0.73 g x 1 mole = .0040 mole
183 g
2 NaOH
 Ni(OH)2 +
0.0040
XS
0
- 0.0040
- 0.0080
+0.0040
+0.0080
0
XS
0.0040
0.0080
Equation:
Ni(NO3)2
Before:
Change:
After:
+
NaNO3 produced: 0.0080 mole x 85.0 g
1 mole
Modeling Chemistry
1
2 NaNO3
0
=
0.68 g
U8 ws 4 v1.5
5. In the copper–silver nitrate lab copper metal and silver nitrate solution reacted to
produce silver metal and copper(II) nitrate in solution.
A student placed a copper wire with a mass of 2.93 g in the reaction test tube. The
silver nitration solution contained 1.41 g of silver nitrate.
He obtained 0.87 g of silver metal. Calculate the percent yield. 2.93 g x 1 mole = 0.0461 mole
Equation:
Cu
+
Before:
0.0461
Change:
- 0.00415
After:
2 AgNO3  2 Ag
0.00830
0
- 0.00830
XS
+
0
+ 0.00830
+0.00461
0.00830
0.00461
0
63.5 g
Cu(NO3)2
theoretical yield: 0.00830 mole x 107.9g = 0.896 g
1 mole
Cu
1.41 g x 1 mole = 0.00830 mole
170 g
AgNO3
percent yield: = 0.87 g x 100% = 97%
0.896 g
6. When hydrochloric acid (HCl) is added to sodium hydrogen carbonate, water, aqueous
sodium chloride and carbon dioxide gas are the products. What is the percent yield if
4.68 g of CO2 are collected when 10.0 g of sodium hydrogen carbonate reacts with
excess HCl?
10.0 g x 1 mole = 0.119 mole
84 g
Equation:
HCl
Before:
XS
Change:
After:
+
NaHCO3

H 2O
0.119 0
+
0
NaCl
+
0
0
- 0.119
- 0.119
+ 0.119
+ 0.119
XS
0
0.119
0.119
theoretical yield: 0.119 mole x 44.0g = 5.24 g
1 mole
NaHCO3
CO2
+ 0.119
0.119
percent yield: = 4.68 g x 100% = 89.3%
5.24 g
7. Phosphorus and bromine react vigorously together to form phosphorus tribromide. If
5.0 g of phosphorus and 35 g of bromine react, how many grams of PBr3 could be
produced?
5.0 g x 1 mole = 0.161 mole
Equation:
2P
+
3 Br2
 2 PBr3
Before:
0.161
0.219
Change:
- 0.146
- 0.219
+ 0.146
0.015
0
0.146
After:
31.0 g
0
35 g x 1 mole = 0.219 mole
160 g
0.146 mole x 271 g = 40. g PBr3
1 mole
8. Zinc sulfide and oxygen gas react to form zinc oxide and sulfur dioxide. Determine the
amount of ZnO that should be produced in a reaction between 46.5 g of ZnS and 13.3 g
46.5 g x 1 mole = 0.477 mole ZnS
of oxygen. What is the mass of the xs reactant?
97.5 g
Equation:
2 ZnS
+ 3 O2
Before:
0.477
0.416
Change:
- 0.277
After:
0.200
 2 ZnO
+ 2 SO2
0
0
- 0.416
+ 0.277
+ 0.277
0
0.277
0.277
13.3 g x 1 mole = 0.416 mole O2
32 g
0.277 mole x 81.4 g = 22.5 g ZnO
1 mole
0.200 mole x 97.5 g = 19.5 g ZnS
1 mole
Modeling Chemistry
2
U8 ws 4 v1.5