Question

Explain the action of soap with hard water.

Answer 1

• The cleaning capacity of soap is reduced when used in hard water. 
• Soaps are sodium or potassium salts of long chain fatty acids. 
• When soap is added to hard water, the divalent magnesium and calcium cations present in hard water react with soap.
• The sodium salts present in soaps are converted to their corresponding magnesium and calcium salts which are precipitated as scum or precipitate. 

M²⁺ + 2RCOONa (RCOO)₂ M_(s) + 2Na⁺_(aq) ; 

Where, M Ca or Mg; 

R = C₁₇ H₃₅ .