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प्रश्न
Why is soap not suitable for washing clothes when the water is hard?
उत्तर
(1) Hard water contains calcium and magnesium salts; and, when a soap is used for washing clothes with hard water, a good amount of it gets utilised in reacting with the calcium and magnesium ions to form an insoluble scum. So, a large amount of soap gets wasted in this process.
(2) The curdy precipitate called scum, produced by the reaction of hard water on soap, sticks to the clothes making them difficult to be cleaned. Therefore, soaps are not suitable for washing clothes in hard water.
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संबंधित प्रश्न
While preparing soap a small quantity of common salt is generally added to the reaction mixture of vegetable oil and sodium hydroxide. Which one of the following may be the purpose of adding common salt?
(A) To reduce the basic nature of the soap
(B) To make the soap neutral
(C) To enhance the cleansing power of the soap
(D) To favour the precipitation of the soap
A student takes about 4 ml of distilled water in four test tubes marked P, Q, R and S. He then dissolves in each test tube an equal amount of one salt in one test tube, namely sodium sulphate in P, potassium sulphate in Q, calcium sulphate in R and magnesium sulphate in S. After that he adds an equal amount of soap solution in each test tube. On shaking each of these test tubes well, he observes a good amount of lather (foam) in the test tube marked
(A) P and Q
(B) Q and R
(C) P, Q and S
(D) P, R and S
People use a variety of methods to wash clothes. Usually after adding the soap, they ‘beat’ the clothes on a stone, or beat it with a paddle, scrub with a brush or the mixture is agitated in a washing machine. Why is agitation necessary to get clean clothes?
State one use of esterfication process.
A student requires hard water for an experiment in his laboratory which is not available in the neighbouring area. In the laboratory there are some salts, which when dissolved in distilled water can convert it into hard water. Select from the following groups of salts, a group, each salt of which when dissolved in distilled water will make it hard.
(A) Sodium chloride, Potassium chloride
(B) Sodium sulphate, Potassium sulphate
(C) Sodium sulphate, Calcium sulphate
(D) Calcium sulphate, Calcium chloride
What change will you observe if you test soap solution with a litmus paper (red and blue)? Give reason for your observation.
How is soap made? Write a word equation involved in soap making.
Give the reason of formation of scum when soaps are used with hard water.
Write an answer to the following question.
Name three chemicals responsible for the surface activity of various detergents.
What are the differences between Bath soap and soap for washing clothes?
