Other alkaline solutions
2 marks · EasyMagnesium hydroxide ([32mMg(OH)_2[0m) is often used as an antacid. It does not dissolve well in water, but any dissolved part is alkaline. Explain why a solution of magnesium hydroxide is alkaline.
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Because it releases hydroxide ions (OH^-) into the solution, which make solutions alkaline.
Also accept: Because it dissociates to form hydroxide ions in solution, raising pH above 7.
Common mistakes: States 'magnesium hydroxide' without mentioning OH^-
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Marking points
M1 · 1 mark · Mentions that magnesium hydroxide releases/dissociates to form hydroxide ions (OH^-) in water.
A1 · 1 mark · Explains that hydroxide ions are responsible for alkalinity/raise pH above 7.
Worked solution
Magnesium hydroxide, when dissolved, dissociates to give hydroxide ions (OH^-) in solution:
The presence of OH^- ions makes the solution alkaline.