A chemical plant's wastewater stream contains equal concentrations of dissolved sulfate ions (SO42−\text{SO}_4^{2-}SO42−) and hydroxide ions (OH−\text{OH}^-OH−). A chemist wishes to selectively precipitate the sulfate ions as a solid Group 2 metal salt, while ensuring that the hydroxide ions remain dissolved in the solution.
Which Group 2 chloride should be added to achieve this selective precipitation, and why?
BaCl2\text{BaCl}_2BaCl2, because the solubility of Group 2 sulfates decreases down the group, while the solubility of Group 2 hydroxides increases down the group.
MgCl2\text{MgCl}_2MgCl2, because the solubility of Group 2 sulfates increases down the group, while the solubility of Group 2 hydroxides decreases down the group.
BaCl2\text{BaCl}_2BaCl2, because the solubility of both Group 2 sulfates and hydroxides decreases down the group.
MgCl2\text{MgCl}_2MgCl2, because the solubility of both Group 2 sulfates and hydroxides increases down the group.
14 exam-style questions on OCR A A Level Chemistry Group 2. Each one has a worked solution and a mark scheme showing where the marks go.