Barium Sulphate BP

BaSO4 --- 233.4 --- 7727-43-7

CHARACTERS

Appearance
Fine, white or almost white powder, free from gritty particles.
Solubility
Practically insoluble in water and in organic solvents. It is very slightly soluble in acids and in solutions of alkali hydroxides.

IDENTIFICATION

A.Boil a suspension of 0.2 g with 5 ml of a 500 g/l solution of sodium carbonate for 5 min, add 10 ml of water, filter and acidify a part of the filtrate with dilute hydrochloric acid. The solution gives the reactions of sulphates.
B. Wash the residue collected in the preceding test with 3 successive small quantities of water. To the residue add 5 ml of dilute hydrochloric acid, filter and add to the filtrate 0.3 ml of dilute sulphuric acid. A white precipitate is formed that is insoluble in dilute sodium hydroxide solution.

TESTS

Solution S
To 20.0 g add 40 ml of distilled water and 60 ml of dilute acetic acid. Boil for 5 min, filter and dilute the cooled filtrate to 100 ml with distilled water.
Acidity or alkalinity
Heat 5.0 g with 20 ml of carbon dioxide-free water on a water-bath for 5 min and  filter. To 10 ml of the filtrate add 0.05 ml of bromothymol blue solution. Not more than 0.5 ml of 0.01 M hydrochloric acid or 0.01 M sodium hydroxide is required to change the colour of the indicator.
Acid-soluble substances
Maximum 0.3 per cent.
Oxidizable sulphur compounds
Shake 1.0 g with 5 ml of water for 30 s and filter. To the filtrate add 0.1 ml of starch  solution, dissolve 0.1 g of potassium iodide in the mixture, add 1.0 ml of a freshly prepared 3.6 mg/l solution of potassium iodate and 1 ml of 1 M hydrochloric  acid and shake well. The colour of the solution is more intense than that of a  standard prepared at the same time and in the same manner, but omitting the  potassium iodate.
Soluble Barium salts
Maximum 10 ppm.
Heavy metals
Maximum 10 ppm.
Loss on ignition
Maximum 2.0 per cent, determined on 1.0 g at 600 ± 50 C.

Barium Sulfate USP

BaSO4 233.39
Sulfuric acid, barium salt (1:1) --- [7727-43-7].

Barium Sulfate contains not less than 97.5 percent and not more than 100.5 percent of BaSO4.

Identification

A: Mix 0.5 g with 2 g each of anhydrous sodium carbonate and anhydrous potassium carbonate, heat the mixture in a crucible until fusion is complete, treat the resulting fused mass with hot water and filter: the filtrate, acidified with hydrochloric acid, meets the requirements of the tests for Sulfate.
B: Dissolve a portion of the well-washed residue from Identification test A in 6 N acetic acid: the solution meets the requirements of the tests for Barium.
pH: between 3.5 and 10.0, in a 10% (w/w) aqueous suspension.
Heavy metals— Boil 4.0 g with a mixture of 2 mL of glacial acetic acid and 48 mL of water for 10 minutes. Dilute with water to 50 mL, filter, and use 25 mL of the filtrate: the limit is 0.001%.
Limit of sulfide— To 10 g in a 500-mL conical flask add 100 mL of 0.3 N hydrochloric acid. Cover the mouth of the flask with a circle of filter paper that has been moistened at the area over the mouth of the flask with 0.15 mL of lead acetate TS, the paper being held in place with a string tied around the neck of the flask. Boil the mixture gently for 10 minutes, taking care to avoid spattering the paper. Any darkening of the paper is not greater than that produced by a similarly treated control consisting of 100 mL of 0.3 N hydrochloric acid containing 5 :g of sulfide: not more than 0.5µg per g is found.
Limit of acid-soluble substances— Cool the mixture obtained in the test for Limit of sulfide, add water to restore approximately the original volume, and filter it through paper that previously has been washed with a mixture of 10 mL of 3 N hydrochloric acid and 90 mL of water, returning the first portions, if necessary, to obtain a clear filtrate. Evaporate 50 mL of the filtrate on a steam bath to dryness, and add 2 drops of hydrochloric acid and 10 mL of hot water. Filter again through acid washed paper, prepared as directed above, wash the filter with 10 mL of hot water, and evaporate the combined filtrate and washings in a tarred dish on a steam bath to dryness. The residue, when dried at 105 for 1 hour, weighs not more than 15 mg: not more than 0.3% of acid-soluble substances is found.
Limit of soluble Barium salts— Treat the residue obtained in the test for Limit of acid-soluble substances with 10 mL of water, pass the solution through a filter previously washed with 100 mL of 0.3 N hydrochloric acid, and add 0.5 mL of 2 N sulfuric acid. Any turbidity formed within 30 minutes is not greater than that produced in a similarly treated control consisting of 10 mL of water containing 0.5 mL of 2 N sulfuric acid and 50 :g of barium: not more than 0.001% of soluble barium salts is found.