Which of the following statements is/are correct?1. Soaps used for cleaning purpose are sodium or potassium salts of long-chain fatty acids, e.g., stearic, oleic and palmitic acids. 2. Soaps do not work in hard water as it contains calcium and sulfate ions.
Soaps used for cleaning purposes are sodium or potassium salts of long-chain fatty acids , e.g. stearic, oleic, and palmitic acids . Hence, Statement1 is correct. Soaps containing sodium salts are formed by heating fat (i.e. glyceryl ester of fatty acid ) with an aqueous sodium hydroxide solution . This reaction is known as saponification . In this reaction, esters of fatty acids are hydrolyzed and the soap obtained remains in colloidal form . It is precipitated from the solution by adding sodium chloride. The solution left after removing the soap contains glycerol, which can be recovered by fractional distillation . Only sodium and potassium soaps are soluble in water and are used for cleaning purposes. Generally, potassium soaps are soft to the skin than sodium soaps . These can be prepared by using a potassium hydroxide solution in place of sodium hydroxide . Hard water contains calcium and magnesium ions. Hence, Statement 2 is incorrect. These ions form insoluble calcium and magnesium soaps respectively when sodium or potassium soaps are dissolved in hard water . These insoluble soaps separate as scum in water and are useless as a cleansing agent. In fact, these are a hindrance to good washing , because they precipitate adheres onto the fibre of the cloth as gummy mass. Hair washed with hard water looks dull because of this sticky precipitate . Dye does not absorb evenly on cloth washed with soap using hard water, because of this gummy mass .