Question

excess of soap soluion in hard water leads to the formation of lather in hard water.give reason

Answer 1

We know that, the simple soaps are generally the sodium(Na) or Potassium (K) salts of higher fatty acids and the hard water contains Ca and Mg ions which are generally larger than the Na/K ions. When soaps are used in hard water, the Ca⁺² and Mg⁺² ions react with soap and replace other ions by making crudy white precipitate of Ca⁺² and Mg⁺² soaps. It means , these larger ions react with the soap molecules and make the soap as precipitate and so the water soluble nature of the soap molecules is lost and hence, they dont give lather( foam) with hard water.

This scum dormed by Ca⁺² and Mg⁺² salts, decreases the cleasing action of soap.

In case of excess of soap solution, when number of soap molecules is more than the number of calcium or magnesium ions present in the water there may be formation of lather. This is because all the calcium and magnesium ions has already been used up for formation of precipitate and now they are not available in free state and any more soap added to the water will produce lather.