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 SCUM-
Scum is an insoluble precipitate of calcium and magnesiumsalts of fatty acids
formed by the reaction of soap with hard water.

Soap + Hard water → Calcium salt + Magnesium salt. (Scum)

Chemically, soap combines with calcium and magnesiumions present in hard
waterto form an insoluble precipitate called scum.

When clothes are cleaned with soap using hard water, some of the soap reacts with
calcium and magnesium salts present in hard water to form scum.
So, - very less soap is left behind for cleaning purposes.
- The scum gets deposited on the clothesand hinders the process of cleaning.

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