If the hardness of water is caused by calcium bicarbonate or magnesium bicarbonate, this hardness is called temporary hardness. After the water with temporary hardness is boiled, the calcium bicarbonate in the water generates calcium carbonate. Magnesium bicarbonate becomes MgCO3 in water, which is even more insoluble in water after heating. The hardness of water has decreased.

If the hardness of water is caused by sulfate or chloride of calcium and magnesium, this hardness is called permanent hardness. Heating water with permanent hardness cannot reduce the hardness of water.

Method of reducing water hardness: 1. Drug softening method. (lime and soda ash)

2. Ion exchange method (sulfonated coal)

Adding calcium hydroxide to hard water is an applied chemical softening method. For permanent hard water, there are many calcium and magnesium ions in permanent hard water. After adding calcium hydroxide, magnesium ions are converted into magnesium hydroxide, which is insoluble and easier to remove.

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References:

Chemistry reading materials

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