Testing procedure (Method of analysis) for Bromides, Calcium Salts and Carbonates

Bromides

A. Dissolve a quantity of the substance under examination equivalent to about 3 mg of bromide ion in 2 rn1 of water or use 2 ml of the prescribed solution. Acidify with 2 M nitric acid, add 1 ml of 0.1 M silver nitrate, shake and allow to stand; a curdy, pale yellow precipitate forms. Centrifuge and wash the precipitate rapidly with three quantities, each of 1 ml, of water in subdued light. Suspend the precipitate in 2 ml of water and add 1.5 ml of 10 M ammonia; the precipitate dissolves with difficulty.

B. Dissolve about 10 mg of the substance under examination in 2 ml of water and 1 ml of chlorine solution; bromine is evolved, which is soluble in 2 or 3 drops of chloroform, forming a reddish solution. To the aqueous solution containing the liberated bromine add phenol solution; a white precipitate is produced.

NOTE - 1n testing for bromides in the presence of iodides, all iodine must first be removed by boiling the aqueous solution with an excess of lead dioxide.

Calcium Salts

A. Dissolve 20 mg of the substance under examination in 5 ml of 5 M acetic acid or add 1 ml of glacial acetic acid to 5 ml of the prescribed solution. Add 0.5 rn1 of potassium ferrocyanide solution, the solution remains clear. Add about 50 mg of ammonium chloride; a white, crystalline precipitate is formed.

B. To 5 ml of a 0.4 percent w/v solution of the substance under examination add 0.2 ml of a 2 percent w/v solution of ammonium oxalate; a white precipitate is obtained that is only sparingly soluble in dilute acetic acid but is soluble in hydrochloric acid.

C. Dissolve 20 mg of the substance under examination in the minimum quantity of dilute hydrochloric acid and neutralize with dilute sodium hydroxide solution or use 5 ml of the prescribed solution. Add 5 ml of ammonium carbonate solution; a white precipitate is formed which, after boiling and cooling the mixture, is only sparingly soluble in ammonium chloride solution.

Carbonates

A. Suspend 0.1 g of the substance under examination in a test-tube in 2 ml of water or use 2 ml of the prescribed solution. Add 2 ml of 2 M acetic acid, close the tube immediately using a stopper fitted with a glass tube bent at two right-angles, heat gently and collect the gas in 5 ml of 0.1 M barium hydroxide, a white precipitate is formed that dissolves on the addition of an excess of dilute hydrochloric acid.

B. Treat a solution of the substance under examination with a solution of magnesium sulphate; a white precipitate is formed (distinction from bicarbonates).

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