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calcium sulphate dihydrate
(ph eur monograph 0982)
caso4,2h2o 72.2 10101-41-4
calcium sulphate dihydrate contains not less than 98.0 per cent and not more than the equivalent of 102.0 per cent of caso4,2h2o.
a white, fine powder, very slightly soluble in water, practically insoluble in alcohol.
a. it complies with the test for loss on ignition (see tests).
b. solution s (see tests) gives reaction (a) of sulphates (2.3.1).
c. solution s gives reaction (a) of calcium (2.3.1).
dissolve1.0 gin 50 ml of a 10 per cent v/v solution of hydrochloric acid r by heating at50°cfor 5 min. allow the solution to cool.
acidity or alkalinity
shake1.5 gwith 15 ml of carbon dioxide-free water r for 5 min. allow to stand for 5 min and filter. to 10 ml of the filtrate, add 0.1 ml ofphenolphthalein solution r and 0.25 ml of0.01m sodium hydroxide. the solution is red. add 0.30 ml of0.01m hydrochloric acid. the solution is colourless. add 0.2 ml of methyl red solution r. the solution is reddish-orange.
shake0.5 gwith 15 ml of water r for 5 min. allow to stand for 15 min and filter. dilute 5 ml of the filtrate to 15 ml with water r. the solution complies with the limit test for chlorides (300 ppm).
5 ml of solution s complies with limit test a for arsenic (10 ppm).
to0.25 gadd a mixture of 5 ml of hydrochloric acid r and 20 ml of water r. heat to boiling, cool and filter. 10 ml of the filtrate complies with the limit test for iron (100 ppm).
heavy metals (2.4.8)
to2.5 gadd a mixture of 2 ml of hydrochloric acid r and 15 ml of water r. heat to boiling. cool and then add 0.5 ml of phenolphthalein solution r. cautiously add concentrated ammonia r until the colour changes to pink. add 0.5 ml of glacial acetic acid r and dilute to 25 ml withwater r. filter. 12 ml of the filtrate complies with limit test a for heavy metals (20 ppm). prepare the standard using lead standard solution (2 ppm pb) r.
loss on ignition
18.0 per cent to 22.0 per cent, determined on1.000 gby ignition to constant mass at800°c.
dissolve0.150 gin 120 ml of water r. carry out the complexometric titration of calcium (2.5.11).
1 ml of0.1m sodium edetate is equivalent to 17.22 mg of caso4,2h2o.
action and use