(a) what is rectified spirit?
(b)why does soap not work in hard water?
We cannot entertain more than 5 questions in a subject per day. In case of multiple questions within a query, please post each question individually and let us know where you are getting stuck so that we would be able to explain things better.
Rectified spirit is highly concentrated ethanol which has been purified by means of repeated distillation, a process that is called rectification. It typically contains 95% alcohol by volume. Rectified spirits are used in mixed drinks, in the production of liquors, for medicinal purposes etc.
Answer to your second question:
Soaps when added to water reduce the surface tension of water and allow the formation of lather. There is a certain minimum amount of soap - the critical micelle concentration - that is necessary for the lather to form. That is why if you use soap with really dirty dishes the initial lather disappears, even in soft water.
In case of hard water there are relatively large amounts of calcium and magnesium ions. Each of these ions can react with two soap molecules which form an insoluble precipitate. Since the soap has been effectively removed from solution there is not enough molecules left to form the soap lather.
You have rated this answer /10