CIE AS Chemistry (9701) exams from 2022

Revision Notes

2.2.5 Group 2: Trends in Solubility of Hydroxides & Sulfates

Trends in Solubility in 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 OHions 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 - Table 1_Trends in Solubility in Group 2 Hydroxides & Sulfates, downloadable AS & A Level Chemistry revision notes

  • 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 OHions 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

Group 2 - Trends Group 2 Hydroxide, downloadable AS & A Level Chemistry revision notes

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 decreasing going down the group

 

Group 2 - Trends Group 2 Sulfate, downloadable AS & A Level Chemistry revision notes

Going down the group, the solubility of the sulfates decreases

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