Group 2 metals form alkaline solutions in water. (i) Write the equation for the reaction of calcium oxide with water. (ii) Identify the ion that causes an aqueous solution to be alkaline. (b) The table shows the melting points of some Group 2 metal oxides. compound melting point/ °C --- --- MgO 2825 CaO 2613 SrO 2531 BaO 1923 Explain the trend in the melting points of the oxides down Group 2. (c) Oxygen reacts readily with some metals, but each Group 2 metal requires strong…

Chemistry 9701/22 — February/March 2020

Cambridge AS Level · AS Level Structured Questions · worked solutions for every part, with the mark scheme

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Topics Chemical Bonding · Introduction to Organic Chemistry · Group 2 · Reaction Kinetics · Chemical Periodicity · Equilibria · +13 more

Q1Group 2Chemical BondingReaction KineticsChemical PeriodicityEquilibriaElectrochemistryChemical EnergeticsFree sample

Group 2 metals form alkaline solutions in water.

(a)

(i)

Write the equation for the reaction of calcium oxide with water.

(ii)

Identify the ion that causes an aqueous solution to be alkaline.

(b)

The table shows the melting points of some Group 2 metal oxides.

compound	melting point/ °C
MgO	2825
CaO	2613
SrO	2531
BaO	1923

Explain the trend in the melting points of the oxides down Group 2.

(c)

Oxygen reacts readily with some metals, but each Group 2 metal requires strong heating to start the reaction with oxygen.

Suggest why strong heating is required to start these reactions.

(d)

Beryllium oxide reacts with hydrochloric acid to form molecules of $\text{BeCl}_2$ .

Deduce the bond angle in $\text{BeCl}_2$ .

(e)

Unlike the other oxides of Group 2 metals, beryllium oxide is amphoteric.

(i)

Give the meaning of the term amphoteric.

(ii)

Beryllium oxide and aluminium oxide have similar chemical properties.

The $\text{Be(OH)}_4^{2-}$ anion is a product of the reaction between beryllium oxide and excess concentrated $\text{OH}^-(\text{aq})$ .

Construct an equation for this reaction.

(f)

Magnesium oxide reacts reversibly with chlorine according to the following equation.

2\text{MgO(s)} + 2\text{Cl}_2\text{(g)} \rightleftharpoons 2\text{MgCl}_2\text{(s)} + \text{O}_2\text{(g)}

Under certain conditions, a dynamic equilibrium is established.

(i)

State two features of a reaction that is in dynamic equilibrium.

(ii)

The equilibrium constant, $K_p$ , is given by the following expression.

K_p = \frac{p_{\text{O}_2}}{p_{\text{Cl}_2}^2}

At $1.00 \times 10^5\text{ Pa}$ and $500\text{ K}$ , $70\%$ of the initial amount of $\text{Cl}_2\text{(g)}$ has reacted.

Calculate $K_p$ and state its units.

(g)

Magnesium peroxide, $\text{MgO}_2$ , is made in the following reaction.

\text{MgO(s)} + \text{H}_2\text{O}_2\text{(l)} \rightarrow \text{MgO}_2\text{(s)} + \text{H}_2\text{O(l)} \quad \Delta H = -96\text{ kJ mol}^{-1}

compound	enthalpy change of formation, $\Delta H_f$ / $\text{kJ mol}^{-1}$
MgO(s)	$-602$
$\text{H}_2\text{O}_2\text{(l)}$	$-188$
$\text{H}_2\text{O(l)}$	$-286$

(i)

The peroxide ion is $\text{O}_2^{2-}$ .

Deduce the average oxidation number of oxygen in the peroxide ion.

(ii)

Define the term enthalpy change of formation.

(iii)

Use the data given to calculate the enthalpy change of formation of $\text{MgO}_2\text{(s)}$ .

(iv)

Magnesium peroxide decomposes slowly to form magnesium oxide and oxygen.

\text{MgO}_2\text{(s)} \rightarrow \text{MgO(s)} + \frac{1}{2}\text{O}_2\text{(g)}

Use your answer to (g)(iii) and the data in the table to calculate the enthalpy change of this reaction.

If you were unable to obtain an answer to (g)(iii), use the value $\Delta H_f = -550\text{ kJ mol}^{-1}$ . This is not the correct answer.

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