Trends in Solubility of Group 2 Hydroxides & Sulfates
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:
O2- (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
