Chemistry 0620 · IGCSE · The mole and the Avogadro constant

The mole and the Avogadro constant — practice question

Hydrocarbons are substances made up of carbon and hydrogen only. • 10 cm$^3$ of a gaseous hydrocarbon, $\text{C}_x\text{H}_y$, is burned in 100 cm$^3$ of oxygen, and the oxygen is in excess. • After cooling back to room temperature and pressure, 25 cm$^3$ of oxygen is unreacted, 50 cm$^3$ of carbon dioxide is present and some liquid water is formed. All volumes are measured under identical conditions of temperature and pressure.
(a(i))[1]

What is meant by an excess amount of oxygen?

(a(ii))[1]

What volume of oxygen reacted with the hydrocarbon?

(a(iii))[1]

Fill in the table to show the smallest whole-number ratio of volume of hydrocarbon reacted : volume of oxygen reacted : volume of carbon dioxide produced.

(a(iv))[2]

Use your answer to (a)(iii) to determine the mole ratio in the equation below. Finish the equation and deduce the formula of the hydrocarbon. $\ldots\ldots \, \text{C}_x\text{H}_y(g) + \ldots\ldots \, \text{O}_2(g) \rightarrow \ldots\ldots \, \text{CO}_2(g) + \ldots\ldots \, \text{H}_2\text{O}(l)$ formula of hydrocarbon =

(b(i))[1]

Complete the chemical equation below. $\text{C}_{10}\text{H}_{22} \rightarrow \text{C}_3\text{H}_6 + \ldots\ldots\ldots\ldots$

(b(ii))[1]

What does the term unsaturated mean?

(b(iii))[2]

Describe a test that demonstrates that propene is an unsaturated compound. test result

(c(i))[1]

State which type of polymerisation takes place.

(c(ii))[1]

Deduce the greatest mass of polypropene that could be obtained from 1 kg of propene.

(c(iii))[2]

Give the empirical formula for propene and for polypropene.

Worked solution & mark scheme

This 13-mark question has a full step-by-step worked solution and mark scheme. One marking point: “more than enough to react with the whole hydrocarbon OR some oxygen is left over” …

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