Group 2 carbonates decompose on heating to form the corresponding metal oxide and carbon dioxide. The mechanism for this decomposition involves the carbonate ion breaking down to form carbon dioxide and oxide ions.

Add two curly arrows to the carbonate ion in Figure 2.1 to suggest a mechanism for this decomposition.

Draw with the mouse or a finger.

2(b)Group 1 Group 2 MetalsMedium2 marks

The radii of some cations are shown in Table 2.1.

cation	Ca $^{2 +}$	Cu $^{2 +}$	Pb $^{2 +}$
radius / nm	0.099	0.073	0.120

Use the data in Table 2.1 to predict the trend in thermal stability of the metal carbonates containing these cations. Explain your answer.

Answer

0 words

2(c)Group 1 Group 2 MetalsMedium3 marks

Suggest why the solubility of the Group 2 sulfates decreases down the group.

Answer

0 words

2(d)(i)Solubility Equilibria KspMedium2 marks

Magnesium hydroxide, Mg(OH)

_{2}

, is sparingly soluble in water at 298 K. Write the expression for the solubility product,

K_{s p}

, of Mg(OH)

_{2}

, and state the units for

K_{s p}

K_{s p}

Units

2(d)(ii)Solubility Equilibria KspMedium1 mark

A saturated solution of Mg(OH)

_{2}

has a pH of 10.35 at 298 K. Calculate the concentration of hydroxide ions, OH

^{-}

, in mol dm

^{- 3}

, in this solution.

Concentration of OH

^{-}

2(d)(iii)Solubility Equilibria KspMedium1 mark

Use your answers to 2(d)(i) and 2(d)(ii) to calculate the value of

K_{s p}

for Mg(OH)

_{2}

K_{s p}

for Mg(OH)

_{2}