Identification tests of magnesium hydroxide

Learn the identification tests of magnesium hydroxide through a laboratory experiment or practical.

Aim:

To carry out identification tests of magnesium hydroxide on the given sample.

Reference: Indian Pharmacopoeia (IP) 2010

Requirements:

Glasswares and miscellaneous:

Test tube, test tube stand, holder, measuring cylinder, pipette, glass rod, dropper, rubber stopper, and balance, etc.

Chemicals:

Magnesium hydroxide (Mg(OH)2), Nitric acid (HNO3), sodium hydroxide (NaOH), ammonia solution (NH3), ammonium chloride (NH4Cl), and disodium hydrogen phosphate (Na2HPO4), etc.

Principle of identification tests of magnesium hydroxide:

The formation and dissolution of various precipitates is the principle involved in the identification of Mg(OH)2.

• The first stage involves an acid-base reaction between Mg(OH)2 and HNO3, which results in the formation of the salt Mg(NO3)2.
• The generated Mg(NO3)2 interacts with dilute ammonia in the second stage to re-form Mg(OH)2.
• In the third stage, Mg(OH)2 in the form of white precipitate interact with NH4Cl to form a salt, MgCl2.
• MgCl2reacts with Na2HPO4 to create magnesium hydrogen phosphate crystals in the fourth stage.

Preparation of chemicals:

Preparation of 2 M nitric acid:

Take 12.60 ml of nitric acid using a pipette and dilute to 100.00 ml of distilled water in a volumetric flask, and properly mixing it.

Preparation of 2 M sodium hydroxide solution:

Take 08.00 gm of NaOH and dissolve to 100.00 ml of distilled water in a volumetric flask, and properly mixing it.

Preparation of dilute ammonia solution:

Take 42.50 ml of strong ammonia solution and dilute to 100.00 ml of distilled water in a volumetric flask, and properly mixing it.

Preparation of 2 M ammonium chloride solution:

Take 10.70 gm of ammonium chloride and dissolve to 100.00 ml of distilled water in a volumetric flask, and properly mixing it.

Preparation of 0.25 M disodium hydrogen phosphate:

Take 08.95 gm of disodium hydrogen phosphate and dissolve to 100.00 ml of distilled water in a volumetric flask, and properly mixing it.

Procedure for identification of magnesium hydroxide:

1. Take 15.00 mg magnesium hydroxide and dissolved in 02.00 ml of 2 M nitric acid solution, neutralized it with 2 M sodium hydroxide.
2. Add 01.00 ml of dilute ammonia solution by which white precipitate forms. Re-dissolve it by adding 1 ml of 2M ammonium chloride.
3. Add 01.00 ml of 0.25 M disodium hydrogen phosphate by which a white crystalline precipitate is formed.

Observations:

1. Addition of nitric acid produces a clear/turbid solution.

2. Addition of dilute ammonia solution produces a clear/turbid solution.

3. Addition of ammonium chloride produces a clear/turbid solution.

4. Addition of disodium hydrogen phosphate produces a clear/turbid solution.

Results:

The given sample passes/fails identification tests as per IP 2010. Therefore, the given sample is of..............................

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