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Chemical Formula

CaSO4 2H2O 

Molecular Weight

172.27 

[Compositional Specifications of Calcium Sulfate]

Content

Calcium Sulfate contains 98.0～105.0% of calcium sulfate (CaSO4·2H2O). 

Description

Calcium Sulfate occurs as a white to light yellow-white powder or crystalline powder.  

Identification

To1 gof Calcium Sulfate, add 100 ml of water, shake well, and filter. The filtrate responds to the tests for Calcium Salt and Sulfate.  

Purity

(1) Clarity of Solution : Test Solution Weigh0.2 gof Calcium Sulfate, add 10 ml of diluted hydrochloric acid, and dissolve while heating. The turbidity of test solution should not be more than almost clear. 
     
(2) Free alkali : Weigh0.5 gof Calcium Sulfate, add 100 ml of water, shake, filter, measure 10 ml of the filtrate, and add 1 drop of phenolphthalein solution. No pink color develops. 
     
(3) Chloride : Test Solution Weigh0.2 gof Calcium Sulfate, add 20 ml of water, shake well, filter, and measure 5 ml of the filtrate. 6 ml of diluted nitric acid is added, test solution. The solution tested for chlorides, its content should not be more than the amount that corresponds to 0.3 ml of 0.01 N hydrochloric acid. 
(4) Carbonate : Weigh0.5 gof Calcium Sulfate, add 5 ml of diluted hydrochloric acid. No effervescence occurs. 
     
(5) Arsenic : Weigh1 gof Calcium Sulfate, add water and 6 ml of hydrochloric acid, dissolve while heating on a water bath, cool, and add water to make exactly 40 ml. 10 ml of which is test solution. Test Solution is tested for arsenic and the content should not be more than 4ppm. 
(6) Heavy metals : Test Solution Weigh2 gof Calcium Sulfate, add 5 ml of water and 1 ml of hydrochloric acid, dissolve while boiling, cool, filter, neutralize the filtrate with ammonia solution. add 2 ml of diluted acetic acid and water to make 50 ml, and filter if necessary. This solution as the test Solution. This Test Solution is tested for heavy metals and its content should not be more than 10ppm. 

Loss on Ignition

The weight loss of Calcium Sulfate should be 18～24% 

Assay

Weigh accurately about1 gof Calcium Sulfate, add 40 ml of diluted hydrochloric acid, dissolve while heating on a water bath, cool, and add water to make exactly 100 ml. Proceed as directed in under Calcium Salt Determination, using this solution as the test solution. 
                    0.05 MEDTA 1 ml = 8.609 mg of CaSO4·2H2O