Trends in Solubility of Group 2 Hydroxides & Sulfates (CIE AS Chemistry)

Group 2 hydroxides

• Going down the group, the solutions formed from the reaction of Group 2 oxides with water become more alkaline
• When the oxides are dissolved in water, the following ionic reaction takes place:

O^2- (aq) + H₂O(l) → 2OH^- (aq)

• The higher the concentration of OH^- ions formed, the more alkaline the solution
• The alkalinity of the formed solution can therefore be explained by the solubility of the Group 2 hydroxides

Solubility of the Group 2 hydroxides table

Group 2 hydroxide	Solubility at 298 K (mol / 100 g of water)
Mg(OH)2	2.0 x 10–5
Ca(OH)2	1.5 x 10–3
Sr(OH)2	3.4 x 10–3
Ba(OH)2	1.5 x 10–2

• The hydroxides dissolve in water as follows:

X(OH)₂ (aq) → X (aq) + 2OH^– (aq)

• • Where X is the Group 2 element
• When the metal oxides react with water, a Group 2 hydroxide is formed
• Going down the group, the solubility of these hydroxides increases
• This means that the concentration of OH^- ions increases, increasing the pH of the solution
• As a result, going down the group, the alkalinity of the solution formed increases when Group 2 oxides react with water

The solubility of the Group 2 hydroxides 

Going down the group, the solubility of the hydroxides increases which means that the solutions formed from the reactions of the Group 2 metal oxides and water become more alkaline going down the group

Group 2 sulfates

• The solubility of the Group 2 sulfates decreases going down the group

The solubility of the Group 2 sulfates

 

Going down the group, the solubility of the sulfates decreases