Explain why washing clothes with hard water is not effective.

(N/A) Hard water contains dissolved salts of calcium $(Ca^{2+})$ and magnesium $(Mg^{2+})$ ions. When soap is added to hard water,these ions react with the soap molecules to form an insoluble precipitate known as scum. Because the soap is consumed in forming this scum,it is unable to form a lather with the water,which is necessary for cleaning clothes. Consequently,a large amount of soap is wasted,and the cleaning process becomes ineffective.