Chemistry 9701 · AS & A Level · Group 17

Group 17 — practice question

A metal from Group 2 reacts with bromine to make the crystalline compound $\text{MBr}_2$. An excess of aqueous $\text{AgNO}_3$ is then added to a solution of $\text{MBr}_2$, causing a precipitate to appear. The mixture is filtered, the precipitate is dried, and its mass is measured.
(a)[2]

State the precipitate's formula and colour.

(b)[1]

Finish the equation to show the reaction between $\text{MBr}_2$ and $\text{AgNO}_3$. $\ldots\,\text{MBr}_2 + \ldots\,\text{AgNO}_3 \rightarrow \ldots$

(c)[3]

A $0.250\,\text{g}$ sample of pure $\text{MBr}_2$ contains $8.415 \times 10^{-4}\,\text{mol}$ of $\text{MBr}_2$. Calculate the relative formula mass, $M_r$, of $\text{MBr}_2$. Use the result to identify $\text{M}$. Show your working.

(d(i))[1]

Describe what is observed when chlorine gas is bubbled into an aqueous solution of $\text{MBr}_2$.

(d(ii))[1]

Name the type of reaction that takes place when $\text{MBr}_2$ reacts with chlorine gas.

(e)[2]

Compound $Y$ is a pure insoluble solid that contains halide ions. One reagent is added straight to compound $Y$ to find out which halide ion is present. Identify the reagent added. State the observation that would confirm $Y$ contains bromide ions.

(f(i))[3]

Three separate $1.0\,\text{g}$ samples of different magnesium salts are tested so that the anion in each sample can be identified. Explain how heating is used to identify which sample is: • $\text{MgCO}_3$ • $\text{Mg(NO}_3)_2$ • $\text{MgO}$

(f(ii))[1]

Complete the electron configuration for the magnesium cation in these salts. $1s^2\,\ldots$

(g)[2]

A sample of $\text{MgCO}_3(s)$ is told apart from a sample of $\text{Mg(OH)}_2(s)$ by adding a small amount of each solid to $\text{HCl(aq)}$. State one similarity and one difference in these two reactions.

Worked solution & mark scheme

This 16-mark question has a full step-by-step worked solution and mark scheme. One marking point: cream-coloured precipitate

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