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प्रश्न
Give a scientific explanation.
Soap forms a precipitate in hard water.
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उत्तर
When soap is mixed with hard water calcium and magnesium salts of fatty acids are formed. These being water insoluble they form a precipitate and that is why lather is not formed.
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संबंधित प्रश्न
List two problems that arise due to the use of detergents instead of soaps.
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
In a locality, hard water, required for an experiment, is not available. However, the following salts are available in the school laboratory:
1. Sodium sulphate
2. Calcium sulphate
3. Magnesium chloride
4. Sodium chloride
5. Calcium chloride
6. Potassium sulphate
Which of the above salts may be dissolved in water to obtain hard water for the experiment?
(A) 2, 3 and 5
(B) 1, 2 and 5
(C) 1, 2, 4 and 6
(D) 3 and 5 only
Would you be able to check if water is hard by using a detergent?
What change will you observe if you test soap with litmus paper (red and blue)?
Explain the cleansing action of soap. Draw diagrams to illustrate your answer.
In a soap micelle, the soap molecules are arranged radially with:
(a) ionic ends directed towards the centre and hydrocarbon ends directed outwards
(b) hydrocarbon ends directed towards the centre and ionic ends directed outwards
(c) both ionic ends and hydrocarbon ends directed toward the centre
(d) both hydrocarbon ends and ionic ends directed outwards
The chemical which is not required for the preparation of soap in the laboratory is:
(a) vegetable oil
(b) baking soda
(c) caustic soda
(d) common salt
Which one of the following sets of materials can be used to prepare soap?
(A) Neem oil and calcium hydroxide
(B) Castor oil and sodium hydroxide
(C) Mineral oil and sodium hydroxide
(D) Neem oil and magnesium hydroxide
A student takes 4 mL of distilled water in each of four test tubes I, II, III and IV, and then dissolves an equal amount of four different salts namely NaCl in I, CaCl2 in II, MgCl2 in III and KCl in IV. He then adds 8 drops of the given soap solution to each test tube and shakes the contents of the test tube 10 times. In which test tubes will enough lather (foam) be formed ?
(A) I and II
(B) II and III
(C) I and IV
(D) III and IV
What are detergents chemically? List two merits and two demerits of using detergents for cleansing. State the reason for the suitability of detergents for washing, event in the case of water having calcium and magnesium ions.
Differentiate between:
Detergents and Soaps.
What is meant by ‘surface activity’?
What are the differences between Bath soap and soap for washing clothes?
What are the three main constituents of soap?
How does soap clean clothes?
______ to remove strong strains on the clothes.
Why do soaps not work effectively in hard water?
What are the similarities between Soap and synthetic detergent.
