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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Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.
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