Question

1. Automobiles are often implicated as contributors to global warming because they are a source of the greenhouse gas CO2. How many pounds of CO2 would your car release in a year if it was driven 190. miles per week?

Gasoline is a complex mixture of hydrocarbons. In your calculations, assume that gasoline is octane (molecular formula C8H18) and that it is burned completely to CO2 and H2O in the engine of your car. Also assume that the car averages 27.5 miles per gallon and that the density of octane is 0.703 g cm-3.

2. The boride Ni3B4 is made by the direct combination of nickel and boron at high temperature. How much boron must react with excess nickel to prepare 147 g of Ni3B4 if the yield of the reaction is 92.9%?

3. Manganese(III) oxide can be prepared by heating manganese(IV) oxide in vacuo at high temperature:
4MnO2 2Mn2O3 + O2

The reaction of 403.2 g of MnO2 yields 336.8 g of Mn2O3. Calculate the theoretical yield of Mn2O3 (assuming complete reaction) and its percentage yield.

4. A sample of 6.612 grams of a compound containing carbon and hydrogen reacts with oxygen at elevated temperatures to yield 21.05 grams of CO2 and 7.757 grams of H2O.

(a) Calculate the masses of C and H in the sample.

(b) Does the compound contain any other elements?

(c) What are the mass percentages of C and H in the compound?

(d) What is the empirical formula of the compound?
Enter the elements in the order presented in the question.

Answer 1

Ans 1

The combustion reaction of octane

2 C8H18 + 25 O2 = 16 CO2 + 18 H2O

car averages per cm3

= 27.5 miles / gallon x 1 gallon/3785.412cm3

= 0.0072647 miles/cm3

density of octane = 0.703 g/cm3

Octane used per mile = density / car average

= (0.703 g/cm3) / (0.0072647 miles/cm3)

= 96.7688 g/miles

driven car = 190 miles / week

Octane used per year = Octane used per mile x driven car

= 96.7688 g/miles x 190 miles / week

= 18386.08 g/week x 52.1429 week/year

= 958703.556 g/year

Moles of octane used per year = mass/molecular weight

= 958703.556/114.23

= 8392.748 mol/year

From the stoichiometry of the reaction (per year)

2 mol C8H18 produces = 16 mol of CO2

8392.748 mol C8H18 produces = 16*8392.748/2

= 67141.98 mol/year of CO2

Mass of CO2 released per year = moles x molecular weight

= 67141.98 mol/year x 44 g/mol

= 2954247.15 g/year x 1lb/453.592g

= 6513 lb/year