How is soap prepared? Why it does not form lather with hard water… - Vidyadip

Question

How is soap prepared? Why it does not form lather with hard water?

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Answer

When oil or animal fat is boiled with an aqueous solution of sodium or potassium hydroxide, sodium or potassium salts of carboxylic acids (fatty acids) are formed.
These salts are called soap.
When soap is mixed with hard water, calcium and magnesium salts of fatty acids are formed.
These being water insoluble, they form a precipitate and that is why lather is not formed.

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