Solubility of Hydroxides & Sulfates (Oxford AQA International A Level Chemistry)
Revision Note
Written by: Philippa Platt
Reviewed by: Stewart Hird
Solubility of Hydroxides & Sulfates
Group 2 hydroxides
The hydroxides dissolve in water as follows:
X(OH)2 (aq) → X (aq) + 2OH– (aq)
When the metal oxides react with water, a Group 2 hydroxide is formed
Going down the group, the solubility of these hydroxides increases
Mg(OH)2 is sparingly soluble
Ba(OH)2 is soluble
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
Solubility of the Group 2 hydroxides table
Group 2 hydroxide | Solubility at 298 K |
|---|---|
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 solubility of the Group 2 hydroxides
Group 2 sulfates
The solubility of the Group 2 sulfates decreases going down the group
Barium sulfate is virtually insoluble
The solubility of the Group 2 sulfates
Examiner Tips and Tricks
The insolubility of barium sulfate is used to test for sulfate ions.
Addition of HCl (aq) followed by BaCl2 (aq) OR HNO3 (aq) followed by BaNO3 (aq) will form a white precipitate of barium sulfate if sulfate ions are present.
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