NCERT Class X Science Class: Chapter –4. Carbon and its Compounds – Part-13

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Question 51:

Esters are sweet-smelling substances and are used in making perfumes. Suggest some activity and the reaction involved for the preparation of an ester with well labeled diagram.

Answer:

Activity:

  • Take ethanol (absolute alcohol) and glacial acetic acid along with a few drops of concentrated sulphuric acid in a test tube.

  • Warm in a water-bath at about for at least minutes as shown in the Figure (It should not be heated directly on flame as the vapours of ethanol catch fire)

  • Pour into a beaker containing of water and smell the resulting mixture.

Image Diagram of reaction of ethanoic acid and ethanol

Image Diagram of Reaction of Ethanoic Acid and Ethanol

Image Diagram of reaction of ethanoic acid and ethanol

Question 52:

A compound C (molecular formula, reacts with – metal to form a compound R and evolves a gas which burns with a pop sound. Compound C on treatment with an alcohol A in presence of an acid forms a sweet smelling compound S (molecular formula, . On addition of to C, it also gives R and water. S on treatment with solution gives back R and A. Identify C, R, A, S and write down the reactions involved.

Answer:

  • C — Ethanoic acid

  • R — Sodium salt of ethanoic acid (sodium acetate) and gas evolved is hydrogen

  • A — Methanol

  • S — Ester (Methyl acetate)

(A)>

(B)>

(C)>

(D)>

Question 53:

Look at Figure and answer the following questions

  1. What change would you observe in the calcium hydroxide solution taken in tube B?

  2. Write the reaction involved in test tubes A and B respectively.

  3. If ethanol is given instead of ethanoic acid, would you expect the same change?

  4. How can a solution of lime water be prepared in the laboratory?

Image calcium hydroxide solution

Image Calcium Hydroxide Solution

Image calcium hydroxide solution

Answer:

(a) It will turn milky

When CO2is passed through calcium hydroxide solution (taken in test tube B), i.e., limewater, it turns milky due to the formation of insoluble calcium carbonate

(b)

(Test tube A)

(Test tube B) With excess , milkiness disappears.

(c) If ethanol is taken instead of ethanoic acid, no change will occur because ethanol is a very weak acid and hence cannot decompose to give gas.

As do not react, a similar change is not expected

(d) The lime water is prepared by dissolving calcium oxide in water and decanting the supernatent liquid.

When quick lime is added to water in a test tube. Some of it will dissolve to form calcium hydroxide (lime water) while majority of it remains suspended. Filter the solution. The clear solution thus obtained is called lime water