Question

Explain the formation of scum when hard water is treated with soap.

Answer 1

Olá User.
Here's your answer.

✴ Soaps are sodium or potassium salts of higher fatty acids. 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.

${Ca}^{2+} \: + 2RCOONa \: --> \\ (RCOO)2 \: + 2 {Na}^{ + }$
${Mg}^{2+} \: + 2RCOONa \: --> \\ (RCOO)2 \: + {2Na}^{ + }$

HOPE IT HELPS!!
@CHARLIE16.

Answer 2

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. ... The new substance, scum, does not dissolve in water.