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CHEMISTRY THE CENTRAL SCIENCE

CHAPTER 3: STOICHIOMETRY I


#100
The combustion of 1 mole of octane fuel corresponds to the following reaction equation.
C8H8 (l) + 25/2 O2(g) --> 8 CO2 (g) + 9 H2O (g)
You will also need the molar mass of C8H8 = 114.2 g/mol, and CO2 = 44.01 g/mol.
Volume of octane used = 125.0 mi / [19.50 mi/gal] = 6.410 gal
6.410 gal X [3.7854 L/gal] = 24.27 L --> 24.27 X 103 mL
Mass of octane used = 24.27 X 103 mL X [0.690 g/mL] = 1.674 X 104 g
Mol of octane used = 1.674 X 104 g / [114.2 g/mol] = 1.466 X 102 mol
From the reaction equation: 1 mol of octane generates 8 mol of CO2
Mass of CO2 generated : [5.575 X 102 mol X 8] X [44.01 g/mol] = 5.162 X 104 g --> 51.62 kg

#101
The ratio Ag:AgNO3 is 0.634985
This means 0.634985 = [Molar mass of Ag] / [Molar mass of AgNO3]
Molar mass of Ag = 107.8682 g/mol
Molar mass of O = 15.9994 g/mol
Molar mass of NO3 = Ψ + (3 X 15.9994 g/mol)
[107.8682 g/mol] / [107.8682 g/mol + Ψ + (3 X 15.9994 g/mol)]= 0.634985 = [Ag] / [Ag + N + (3 X O)]
[107.8682 g/mol] = 0.634985 X [107.8682 g/mol + Ψ + (3 X 15.9994 g/mol)]
[107.8682 g/mol] = 68.4947 g/mol + 0.634985Ψ + 30.4781 g/mol
[107.8682 g/mol] = 98.9728 g/mol + 0.634985Ψ
[107.8682 g/mol] - 98.9728 g/mol = 0.634985Ψ
[8.8954 g/mol] = 0.634985Ψ
[8.8954 g/mol] / 0.634985 = Ψ --> Ψ = 14.0088 g/mol
Accepted value = 14.0067 g/mol
Absolute error = 14.0088 g/mol - 14.0067 g/mol = +0.0021 g/mol
Relative error = [+0.0021 g/mol / 14.0067 g/mol] X 100 = 0.015 %

#102a
Chemical equations:
Burning sulfur
S(s) + O2(g) --> SO2(g)

Reaction with calcium oxide
SO2(g) + CaO(s) --> CaSO3(s)


#102b
1 ton = 2000 lb, 1 lb = 2200 g
Coal usage per day = 2000 tons X 2000 lb/ton = 4.000 X 106 lb
4.000 X 106 lb / 2.20 lb/kg = 1.82 X 106 kg = 1.82 X 109 g
Since this coal is 2.5 % sulfur by mass,
Grams of sulfur burnt per day = 1.82 X 109 g X 0.0250 = 4.545 X 107 g
Mol of sulfur burnt per day = 4.545 X 107 g / [32.065 g/mol] = 1.418 X 106 mol
From the chemical equations...
S(s) + O2(g) --> SO2(g); SO2(g) + CaO(s) --> CaSO3(s)

one mol of sulfur generates one mole of calcium sulfite. Using the molar mass of calcium sulfite = 120 g/mol.
Grams of calcium sulfite produced per day = 1.418 X 106 mol X [120 g/mol] = 1.701 X 108 g





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