Solutions Used in Hardness Determination

Solutions Used in Hardness Determination. Standard Solution. It is prepared from a mixture of 0.1 N solutions of calcium and magnesiiun salts in the ratio 3 1. 

Gradually heat a chemically pure preparation of magnesium sulphate heptahydrate in a drying cabinet to 250 C, bringing it up to a constant weight. After cooling in a desiccator, weigh 3.0088 g of 

Dry a chemically pure preparation of calcium carbonate in a drying cabinet at 110 °C and after cooling in a desiccator, weigh 5.004 g. Transfer the substance into a one-litre measuring flask, add about 10 ml of distilled water and then concentrated hydrochloric acid dropwise, avoiding an excess (usually about 8-9 ml are needed) up to complete dissolution of the calcium carbonate. Pour in distilled water up to the mark on the flask. 

To prepare a 0.02 N standard solution of calcium and magnesium salts, pour 75 ml of a 0.1 N calcium chloride solution and 25 ml of a 0.1 TV magnesium sulphate solution into a 500-ml measuring flask, and then add distilled water up to the mark on the flask. 

EDTA Solution. Prepare a 0.02 TV EDTA solution by dissolving 3.75 g of EDTA (complexon) in distilled water in a one-litre measuring flask and then bring the volume up to the mark on the flask. 

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