This video tutorial guides students through solving a free-response question from the 2012 AP Chemistry exam. It covers calculating moles of a hydrocarbon using the ideal gas law, applying Dalton's Law to find partial pressures, and determining the oxygen consumed in a combustion reaction. The tutorial also explains how to balance the chemical equation and calculate the mass of the hydrocarbon. Finally, it predicts the pH of water formed from the combustion process.

What is the formula used to calculate the number of moles of a gas in a vessel?

• n = RT/PV

• n = PRT/V

• n = V/PRT

• n = PV/RT

After adding oxygen to the vessel, the total pressure is 1.4 atm. If the initial pressure of the hydrocarbon was 0.2 atm, what is the partial pressure of oxygen?

• 1.6 atm

• 1.2 atm

• 0.4 atm

• 0.8 atm

How do partial pressures relate to mole ratios in an ideal gas?

• They are inversely proportional.

• They are unrelated.

• They are directly proportional.

• They are equal to mole ratios.

What is the partial pressure of oxygen consumed if the partial pressures of CO2 and H2O are 0.6 atm and 0.8 atm respectively?

• 0.4 atm

• 0.8 atm

• 1.0 atm

• 0.6 atm

What is the balanced chemical equation for the combustion of C3H8?

• C3H8 + 6O2 → 3CO2 + 4H2O

• C3H8 + 4O2 → 3CO2 + 4H2O

• C3H8 + 5O2 → 3CO2 + 4H2O

• C3H8 + 3O2 → 3CO2 + 4H2O

What is the empirical formula of the hydrocarbon if it has 3 carbon atoms and 8 hydrogen atoms?

• C3H8

• C2H6

• C5H12

• C4H10

What is the mass of propane combusted if the number of moles is 6.09 x 10^-3 and the molar mass is 44.1 g/mol?

• 4.69 g

• 5.69 g

• 3.69 g

• 2.69 g

What happens to the pH of water when CO2 dissolves in it?

• It remains unchanged.

• It becomes acidic.

• It becomes basic.

• It becomes neutral.

What is the chemical formula of the acid formed when CO2 dissolves in water?

• H2CO3

• HCl

• HNO3

• H2SO4

Why is the pH of the water less than 7 after the combustion reaction?

• Because CO2 forms a neutral solution.

• Because CO2 does not dissolve in water.

• Because CO2 forms an acidic solution.

• Because CO2 forms a basic solution.