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Soaps and hard water

This type of question, asked 3 times: 2023, 2025, 2026. All 4 questions below, oldest first.

Try each one first, then open its answer.

  1. Question 1

    2023

    34 (b)
    (i) With the help of diagram, show the formation of micelles, when soap is applied on oily dirt. (ii) Take two test tubes X and Y with 10 mL of hard water in each. In test tube ‘X’, add few drops of soap solution and in test tube ‘Y’ add a few drops of detergent solution. Shake both the test tubes for the same period. (1) In which test tube the formation of foam will be more ? Why ? (2) In which test tube is a curdy solid formed ? Why ?

  2. Question 2

    2023

    36 (b)
    (i) What is saponification ? Differentiate between soaps and detergents on the basis of the following : (1) Their chemical composition (2) Their mechanism in hard water (ii) Explain the formation of micelles between oily dirt and soap molecules. Also draw its diagram.

  3. Question 3 (case study, 4 parts)

    2025

    ‘A’ and ‘B’ are two salts used for washing purposes. Salt ‘A’ is used for bathing also. Four test tubes I, II, III and IV as mentioned below are taken. I. Rain water + solution of salt ‘A’ II. Rain water + solution of salt ‘B’ III. Tubewell water + solution of salt ‘A’ IV. Tubewell water + solution of salt ‘B’ The test tubes are shaken one by one almost identically for the same time and the lengths of foam formed in each test tube is noted.
    37 (a)
    In which one of the four test tubes is the foam formed the minimum ?
    37 (b)
    Differentiate between salt A and salt B.
    37 (c) (i)
    What are esters ? What happens when an ester reacts with an alkali (say sodium hydroxide) ? Give chemical equation for the reaction.
    37 (c) (ii)
    What is the cause of hardness of water ? Sometimes it is observed that while bathing foam is formed with difficulty and an insoluble substance is formed. Name this substance and write the cause of its formation.

  4. Question 4

    2026

    20
    While washing dirty clothes by soap, micelles are formed. Select the correct statement about micelles.

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