Chemistry 9701 · AS & A Level · Hydrocarbons

Hydrocarbons — practice question

Propane, $\text{C}_3\text{H}_8$, together with butane, $\text{C}_4\text{H}_{10}$, are constituents of Liquefied Petroleum Gas (LPG), a fuel that is widely used for domestic cooking and heating.
(a(i))[1]

To which class of compounds do these two hydrocarbons belong?

(a(ii))[1]

Write a balanced equation for the complete combustion of butane.

(b(i))[1]

When propane or butane is used for cooking, the saucepan may be coated with a black solid deposit. What is the chemical name of this black solid?

(b(ii))[1]

Write a balanced equation for its formation from butane.

(c)[2]

Propane and butane have different values of standard enthalpy change of combustion. Define the term standard enthalpy change of combustion.

(d(i))[2]

A $125\,\text{cm}^3$ sample of propane gas, at $20\,^{\circ}\text{C}$ and $101\,\text{kPa}$, was completely burned in air. The heat released caused the temperature of $200\,\text{g}$ of water to rise by $13.8\,^{\circ}\text{C}$. Assume that no heat was lost during the experiment. Use the equation $pV = nRT$ to calculate the mass of propane used.

(d(ii))[1]

Use the relevant Data Booklet values to calculate how much heat is released in this experiment.

(d(iii))[2]

Use the data above, together with your answers to (i) and (ii), to calculate the energy released when $1\,\text{mol}$ of propane burns.

(e(i))[2]

The boiling points of methane, ethane, propane, and butane are shown below. Suggest an explanation for why the boiling points increase from methane to butane.

(e(ii))[2]

The butane isomer, 2-methylpropane, $(\text{CH}_3)_3\text{CH}$, has a boiling point of $261\,\text{K}$. Suggest an explanation for the difference between this value and the value for butane in the table above.

Worked solution & mark scheme

This 15-mark question has a full step-by-step worked solution and mark scheme. One marking point: Named as alkanes or paraffins, rather than hydrocarbons

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