Worksheet # 13
Stoichiometry
1. A laboratory method of preparing O2 gas involves the decomposition of solid KClO3
according to the following unbalanced equation: KClO3(s) → KCl(s) + O2(g)
a) How many moles of O2 (g) can be produced by the decomposition of 32.8 g KClO3?
b) How many grams of KClO3 must be decomposed to produce 50.0 g O2?
c) How many grams of KCl are formed when 23.8 grams O2 are formed in the
decomposition of KClO3?
2. Suppose 9.5 g of gaseous C2H2 reacts with excess O2 according to the reaction below. What
is the mass of CO2 produced?
C2H2(g) + O2(g) → CO2(g) + H2O(ℓ)
3. Chlorine gas is made in the laboratory by the reaction of gaseous hydrochloric acid with solid
manganese(IV) oxide to produce aqueous manganese(II) chloride, water, and chlorine. If
13.7 g of manganese(IV) oxide reacts with excess hydrochloric acid, how much chlorine is
formed?
4. Solid bismuth oxide can react with carbon to form bismuth metal and carbon monoxide. How
many grams of bismuth oxide reacted if 60.7 grams of bismuth is formed?
5. Solid chromium(III) oxide can react with gaseous hydrogen sulfide to form solid
chromium(III) sulfide and water. How many grams of chromium(III) oxide are required to
form 83.4 g of chromium(III) sulfide?
6. Solid potassium nitrate decomposes on heating to form solid potassium oxide, nitrogen, and
oxygen. How many grams of potassium nitrate must be heated to form 86.6 kg of oxygen?
7. Solid silver oxide decomposes at temperatures in excess of 300 °C, yielding metallic silver
and oxygen gas. A 3.13 g sample of impure silver oxide yields 0.187 g oxygen. If silver
oxide is the only source of O2, what is the percent silver oxide by mass in the sample?
8. The mineral galena (lead(II) sulfide) can be roasted it in the presence of oxygen to form solid
lead(II) oxide and sulfur dioxide. A 5.77 g sample of impure galena yields 2.11 g lead(II)
oxide. If the galena is the only source of lead(II) oxide, what is the percent galena in the
impure sample?
9. How many moles of CO2 are produced by the reaction of 6.0 mol of MgCO3?
MgCO3 = MgO + CO2
10. Suppose that 1.6 mol Al2(SO4)3 are produced. How many moles of H2O are also produced?
2Al(OH)3 + 3H2SO4 = Al2(SO4)3 + 6H2O
11. According to reaction equation below, how many moles of H2C2O4 react completely with 1.5
mol of KMnO4?
2KMnO4 + 5H2C2O4 + 6HCl = 2MnCl2 + 10 CO2 + 2KCl + 8H2O
Worksheet 13
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12. When 0.45 mol of CO2 are produced by the reaction above, how many grams of H2O are also
produced?
13. How many grams of H2SO4 are required for the complete reaction of 65.0 g of Al(OH)3?
2Al(OH)3 + 3H2SO4 = Al2(SO4)3 + 6H2O
14. How many grams of HCl are required for the complete reaction of 316 g KMnO4?
2KMnO4 + 5H2C2O4 + 6HCl = 2MnCl2 + 10CO2 + 2KCl + 8H2O
Answers to Worksheet #13
Stoichiometry
The first step to stoichiometry is to write and balance the equation. If an equation is given to
you, always check to make sure that it is balanced! Once the equation is balanced, use the
stoichiometric coefficients and dimensional analysis to go from what you know everything about
to what you want to know.
1. 2 KClO3(s) → 2 KCl(s) + 3 O2(g)
1molKClO3 3molO2
= 0.401molO2
a) molO2 = 32.8 gKClO3
122.55 g 2molKClO3
b) mass ( g ) KClO3 = 50.0 gO2
c) mass ( g ) KCl = 23.8 gO2
1molO2 2molKClO3 122.55 g
= 128 gKClO3
32.00 g 3molO2 1molKClO3
1molO2 2molKCl 74.55 g
= 37.0 gKCl
32.00 g 3molO2 1molKCl
2. 2 C2H2(g) + 5 O2(g) → 4 CO2(g) + 2 H2O(ℓ)
1molC2 H 2 4molCO2 44.01g
mass ( g )CO2 = 9.5 gC2 H 2
= 32 gCO2
26.036 g 2molC2 H 2 1molCO2
3. 4 HCl(g) + _ MnO2(s) → _ MnCl2(aq) + 2 H2O(ℓ) + _ Cl2(g)
1molMnO2 1molCl2 70.90 g
mass ( g )Cl2 = 13.7 gMnO2
= 11.2 gCl2
86.94 g 1molMnO2 1molCl2
4. _ Bi2O3(s) + 3 C(s) → 2 Bi(s) + 3 CO(g)
1molBi 1molBi2O3 466.0 g
mass ( g ) Bi2O3 = 60.7 gBi
= 67.7 gBi2O3
209.0 g 2molBi molBi2O3
5. _ Cr2O3(s) + 3 H2S(g) → _ Cr2S3(s) + 3 H2O(ℓ)
1molCr2 S3 1molCr2O3 152.00 g
mass( g )Cr2O3 = 83.4 gCr2 S3
= 63.3 gCr2O3
200.21g 1molCr2 S3 1molCr2O3
6. 4KNO3(s) → 2K2O(s) + 2N2(g) + 5O2(g)
Worksheet 13
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mass( g ) KNO3 = 86.6 gO2
1molO2 4molKNO3 101.11g
= 219 gKNO3
32.00 g 5molO2 1molKNO3
7. 2 Ag2O(s) → 4 Ag(s) + _ O2(g)
1molO2 2molAg 2O 231.8 g
= 2.71gAg 2O
mass ( g ) Ag 2O = 0.187 gO2
32.00 g 1molO2 1molAg 2O
⎛ 2.71g ⎞
% Ag 2O = ⎜
⎟100 = 86.6%
⎝ 3.13g ⎠
8. 2PbS(s) + 3O2(g) → 2PbO(s) + 2SO2(g)
1molPbO 2molPbS 239.27 g
mass ( g ) PbS = 2.11gPbO
= 2.26 gPbS
223.2 g 2molPbO 1molPbS
⎛ 2.26 g ⎞
% PbS = ⎜
⎟100 = 39.2%
⎝ 5.77 g ⎠
⎛
mol CO 2 ⎞
9. 6.0 mol CO 2 ⎜ ? mol CO 2 = 6.0 mol MgCO3 ⋅
⎟
⎜
mol MgCO3 ⎟⎠
⎝
⎛
6 mol H 2 O ⎞
10. 9.6 mol H 2 O ⎜ ? mol H 2O = 1.6 mol Al2 (SO 4 )3 ⋅
⎟
⎜
⎟
mol
Al
(SO
)
2
4
3
⎝
⎠
⎛
5 mol H 2 C2 O5
11. 3.8 mol H 2 C2 O5 ⎜ ? mol H 2C2 O 4 = 1.5 mol KMnO 4 ⋅
⎜
2 mol KMnO 4
⎝
⎞
⎟
⎟
⎠
⎛
8 mol H 2 O 18.0 g H 2 O ⎞
⋅
12. 6.5 g H 2 O ⎜ ? g H 2 O = 0.45 mol CO 2 ⋅
⎟
⎜
mol H 2 O ⎟⎠
10
mol
CO
2
⎝
13. 122 g H 2SO 4
⎛
mol Al(OH)3
⎜ ? g H 2 SO 4 = 65.0 g Al(OH)3 ⋅
⎜
78.0 g Al(OH)3
⎝
⋅
3 mol H 2SO 4
2 mol Al(OH)3
⋅
98.1 g H 2SO 4 ⎞
⎟
mol H 2SO 4 ⎟⎠
⎛
mol K MnO 4
14. 219 g HCl ⎜ ? g HCl = 316 g K MnO 4 ⋅
⎜
158 g KMnO 4
⎝
6 mol HCl
36.5 g HCl ⎞
⋅
⋅
⎟
mol HCl ⎟⎠
2 mol KMnO 4
Worksheet 13
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