Question
(a) (i) Describe and explain the trend in the solubility of the Group 2 hydroxides down the group
Group 2 hydroxides decompose on heating to give the corresponding metal oxide and water vapour.
(ii) Suggest which of $\mathrm{Mg}(\mathrm{OH})_2$ and $\mathrm{Sr}(\mathrm{OH})_2$ will decompose at a lower temperature.
Explain your answer.[2] [Total: 6]
▶️Answer/Explanation
Ans:
(a)(i ) M1 solubility increases down the group
M2 $\Delta H_{\text {latt }}$ and $\Delta H_{\text {hyd }}$ both become less exothermic / less negative
M3 $\Delta H_{\text {latt }}$ changes more (than $\Delta H_{\text {hyd }}$ as $\mathrm{OH}^{-}$being smaller than $\mathrm{M}^{2+}$ )
M4 $\Delta H_{\text {sol }}$ becomes more exothermic / more negative
(a)(ii) M1 $\mathrm{Mg}(\mathrm{OH})_2$ AND $\mathrm{Mg}^{2+}$ has a smaller ionic radii/ $\mathrm{Mg}^{2+}$ has a higher charge density $\mathrm{M} 2 \mathrm{OH}^{-}$ion is polarised/distorted more