How to perform an experiment to distinguish between zinc(II) hydroxide and magnesium hydroxide?
Zn(OH)2 is soluble in an excess of NaOH Or in NH3. Mg(OH)2 is not.
To perform an experiment to distinguish between zinc(II) hydroxide and magnesium hydroxide, you can follow these steps:
1. Prepare solutions: Start by preparing solutions of zinc(II) hydroxide and magnesium hydroxide. You can do this by dissolving zinc sulfate and magnesium sulfate in separate beakers of distilled water. Label the beakers accordingly.
2. Observations of solubility: Begin by comparing the solubility of the two hydroxides. Add a few drops of each solution to separate test tubes. Zinc(II) hydroxide is only slightly soluble in water, so you will see a cloudy precipitate forming. Meanwhile, magnesium hydroxide is more soluble in water, resulting in a clear solution.
3. pH measurement: Use a pH paper or pH meter to test both solutions. Zinc(II) hydroxide is slightly basic, so it will have a pH slightly above 7. On the other hand, magnesium hydroxide is a stronger base and will have a higher pH value compared to zinc(II) hydroxide.
4. Heat test: Take a small amount of each hydroxide and place it on separate ceramic tiles or evaporating dishes. Gently heat the samples using a Bunsen burner or a hot plate. Zinc(II) hydroxide will readily decompose upon heating, resulting in the formation of zinc oxide. It will turn from a white powder to a yellowish color. On the other hand, magnesium hydroxide will not undergo decomposition upon heating and will retain its white color.
By following these steps, you should be able to distinguish between zinc(II) hydroxide and magnesium hydroxide based on their solubility, pH, and behavior upon heating.