Purpose
To demonstrate how pH affects the solubility of Mg(OH)₂.
Procedure
Introduction
Discussion:
- Ask students if they have heard of milk of magnesia.
- Show a bottle and inquire what it is used to treat.
Initial Experiment
Dissolution:
- Take some solid milk of magnesia and add it to water.
- Demonstrate that it does not dissolve well.
- Discuss its solubility product constant (Ksp) and explain that it is sold as a suspension (use a clear bottle for visibility).
Common Ion Effect
Adding NaOH:
- Take 1 M sodium hydroxide (NaOH) and ask students to predict the solubility of Mg(OH)₂.
- Add some milk of magnesia to the NaOH solution.
- Observe the cloudiness and discuss the common ion effect.
Le Chatelier’s Principle
Adding HCl:
- Take 1 M hydrochloric acid (HCl) and explain that it is very similar to stomach acid.
- Repeat the dissolution exercise with HCl and discuss Le Chatelier’s Principle in relation to solubility changes.
Discussion on Dosage
Recommended Dosage:
- Ask students if people always take the recommended dose of milk of magnesia.
- Discuss the effects of an overdose (excess magnesium hydroxide).
- Demonstrate that excess magnesium hydroxide does not dissolve and compare its behavior to that of sodium hydroxide as an antacid.