Name _____________________________
Exam 4 SOLUTION
1. Sulfur dioxide is a primary pollutant and irritant and is a component of acid rain. It often produced
in the smelting process of metal ores, such as in the balanced example reaction below: [14 pts]
2 ZnS(s) + 3 O2(g) → 2 ZnO(s) + 2 SO2(g)
97.48 g/mol
64.07 g/mol
a. If you begin with 1.00 x 102 g of zinc sulfide, how many grams of sulfur dioxide are produced?
1.00 x 102 g ZnS x
2 mol SO 2
64.07 g SO 2
1 mol ZnS
x
x
= 65.7 g SO 2
97.48 g ZnS 2 mol ZnS
1 mol SO 2
b. If 59.39 g of sulfur dioxide are produced in a “batch”, what is the percent yield of this batch?
59.39 g
x 100 = 90.4%
65.7 g
2. Perform the following: [20 pts]
a. Predict the products for the following reactants, and write a balanced molecular equation, with
phase labels.
Potassium sulfide + cobalt (III) chloride → ?
3 K2S(aq) + 2 CoCl3(aq) → Co2S3(s) + 6 KCl(aq)
b. If you begin with 25.7 g of potassium sulfide (110.27 g/mol) and 20.5 g of cobalt (III) chloride
(16528 g/mol), how much insoluble product can be isolated?
K 2S: 25.7 g K 2S x
1 mol K 2S
110.27 g K 2S
CoCl3 : 20.5 g CoCl3 x
x
1 mol Co2S3
3 mol K 2S
1 mol CoCl3
165.28 g CoCl3
x
x
214.07 g Co2S3
1 mol Co2S3
1 mol Co2S3
2 mol CoCl3
x
= 16.6 g Co2S3
214.07 g Co2S3
1 mol Co2S3
= 13.3 g Co2S3
CoCl3 is the limiting reagent, only 13.3 g of Co2S3 can be isolated.
c. Which compound is the limiting reagent?
CoCl3
d. Which compound is in excess?
K2S
Exam 4
Fall 2007
Page 1 of 3
Chemistry 100
Clark College
3. From the starting materials given, predict the products and provide a balanced molecular equation,
including phase labels. Classify the reaction as well (circling as many categories that apply). [30
pts]
a. Hg2(C2H3O2)2 + NH4Cl
Molecular Eq:
Hg2(C2H3O2)2(aq) + 2 NH4Cl(aq) → Hg2Cl2(s) + 2 NH4C2H3O2(aq)
This reaction is a:
(circle all that apply)
Precipitation
Acid-Base
Double Displacement
Single displacement
Redox
b. HNO3 + CaCO3
Molecular Eq:
2 HNO3(aq) + CaCO3(s) → Ca(NO3)2(aq) + H2O(l) + CO2(g)
This reaction is a:
(circle all that apply)
Precipitation
Acid-Base
Double Displacement
Single displacement
Redox
c. Aluminum metal and sulfuric acid
Molecular Eq:
Al(s) + 3 H2SO4(aq) → Al2(SO4)3(aq) + 3 H2(g)
This reaction is a:
(circle all that apply)
Precipitation
Acid-Base
Double Displacement
Single displacement
Redox
4. For each reaction below, provide net ionic equation. [16 pts]
a. 6 Zn (s) + 2 H3PO4 (aq) → 2 Zn3(PO4)2 (s) + 3 H2 (g)
Net Ionic Eq:
6 Zn (s) + 6 H+(aq) + 2 PO4-3 (aq) → 2 Zn3(PO4)2 (s) + 3 H2 (g)
b. 2 NaI (aq) + 2 H2SO4 (aq) + MnO2 (s) → Na2SO4 (aq) + MnSO4 (aq) + I2 (s) + 2 H2O (l)
Net Ionic Eq:
Exam 4
2 I- (aq) + 4 H+(aq) + MnO2 (s) → Mn+2 (aq) + I2 (s) + 2 H2O (l)
Fall 2007
Page 2 of 3
Chemistry 100
Clark College
5. Predict the product of the following reaction, and provide balanced molecular and net ionic
equations. [12 pts]
Iron (II) iodide + lithium hydroxide → ?
Molecular Eq:
FeI2(aq) + 2 LiOH(aq) → Fe(OH)2(s) + 2 LiI(aq)
Net Ionic Eq:
Fe+2(aq) + 2 OH-(aq) → Fe(OH)2(s)
6. When mixed with a solution of lithium bromide, which of the following compounds will form a
precipitate? [4 pts]
a. Ca(OH)2
b. Pb(C2H3O2)2
c. Fe(NO3)3
d. (NH4)2CO3
7. What is the name and formula for the precipitate in the previous problem? [4 pts]
Name
Exam 4
Lead (II) bromide
Formula
Fall 2007
PbBr2
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