Chemistry 5070 · O Level · The mole and the Avogadro constant

The mole and the Avogadro constant — practice question

(a(i))[3]

Magnesium carbonate is added to dilute hydrochloric acid. $\text{MgCO}_3 + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{CO}_2 + \text{H}_2\text{O}$ If $25.0\,\text{cm}^3$ of dilute hydrochloric acid is mixed with excess magnesium carbonate, the carbon dioxide obtained at room temperature and pressure has a volume of $120\,\text{cm}^3$. Calculate the concentration, in $\text{mol dm}^{-3}$, of the dilute hydrochloric acid.

(a(ii))[2]

The reaction is carried out again at a higher temperature, while every other condition remains unchanged. Describe how the rate of reaction changes. Explain your answer using ideas about collisions between particles.

(a(iii))[2]

The reaction is carried out again with hydrochloric acid at a higher concentration, while every other condition remains unchanged. Describe how the rate of reaction changes. Explain your answer using ideas about collisions between particles.

(b)[1]

Duralumin is an alloy made from aluminium, magnesium, copper and manganese. State the meaning of the term alloy.

(c)[1]

Copper is purified through electrolysis with an impure copper anode and a pure copper cathode. Write the ionic equation for the change occurring at the cathode.

(d)[1]

A metal object may be coated by electroplating it with another metal. State one use of electroplating.

Worked solution & mark scheme

This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: Amount of CO$_2$ = 120/24000 or $5 \times 10^{-3}$

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