Question

reaction for scum formed by soap in hard water​

Answer 1

When a soap is used in hard water, a solid substance we call scum forms. This is because charged calcium and magnesium particles (called ions ) present in the water react with soap to form an insoluble substance. Scum builds up on clothes, baths and sinks. Detergents do not form scum.

Answer 2

Answer:

Hardness in water is due to the presence of Ca^2+ and Mg^2+ ions, present as their salts. The soap first reacts with calcium abd magnesium ions to form insoluble precipitate of calcium and magnesium salts of fatty acids which float as an off- white layer over wated. This layer is called scum.

Explanation: