(a) When is a sample of water said to be hard? (b) State one difference between temporary and permanent hardness of water (c) Give one method of removing ha...

(a) A sample of water is said to be hard when it does not readily form a lather (foam) with soap, but instead forms an insoluble scum, because it contains dissolved calcium and magnesium salts.

(b) Temporary hardness is caused by dissolved hydrogen carbonates of calcium and magnesium and can be removed simply by boiling, whereas permanent hardness is caused by the sulphates and chlorides of calcium and magnesium and cannot be removed by boiling.

(c) Hardness can be completely removed by distillation (or by the ion-exchange/permutit method, which removes both temporary and permanent hardness).

(d) Two local materials used for making soap: a vegetable oil or animal fat (for example palm oil or palm-kernel oil) and wood ash (which supplies the alkali/caustic potash).