Question

Discuss the trend of the following:-
(1) Thermal stability of carbonates of group 2 elements
(2) The solubility and the nature of oxides of group 2 elements.

Answer 1

1. The effect of heat on the Group 2 carbonates

All the carbonates in this group undergo thermal decomposition to the metal oxide and carbon dioxide gas. The term "thermal decomposition" describes splitting up a compound by heating it.

All the Group 2 carbonates and their resulting oxides exist as white solids. If "X" represents any one of the elements, the following describes this decomposition:

XCO3(s)→XO(s)+CO2(g)XCO3(s)→XO(s)+CO2(g)

Down the group, the carbonates require more heating to decompose.

• The carbonates become more thermally stable down the group.
  

2.

Group 2 oxides:

• These react with water to form metal hydroxide.

MgO(s)

+

H2O(l)

à

Mg(OH)2(aq)

• These are soluble so dissolve in the water forming an alkali, pH10 - 12