NCERT Class 10 Chapter 3 Carbon CBSE Board Sample Problems Long Answer

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Question

What do you understand by a homologous series? Explain giving one example of homologous series.

OR

Define homologous series of carbon compound. List any two characteristics of a homologous series.

Solution

  • A homologous series is a group or family of compounds which contains the same functional group but have different chain lengths. Thus, these have the same chemical properties but different physical properties that vary in a regular manner.

  • Characteristics of a homologous series are:

    • It has a general formula in terms of number of carbon atoms.

    • It has the same functional group, if any.

    • The members of a homologous series, i.e., homologous, have similar chemical properties.

    • Various homologous can be prepared by the general method of preparation for the series.

    • Two successive (adjacent) homologous differ by 1 carbon atom and 2 hydrogen atoms in their molecular formulae.

    • The member of a homologous series show a gradual change in their physical properties with increase in molecular mass.

Question

Explain the mechanism of the cleaning action of soaps.

Solution

  • Most of the dirt is oily in nature. The oil does not dissolve in water. Moreover, soap molecules are sodium or potassium salts of long chair carboxylic acids, each soap molecule has two parts which are (j) ionic part and (ii) hydrocarbon chain. Ionic part is water-loving or hydrophilic and soluble in water.

  • The hydrocarbon chain is hydrophobic and is not soluble in water. Inside water, the soap molecules have a unique orientation in which its clusters of molecules form a structure called micelle. In the micelle, the ionic parts of soap molecules are oriented towards water and hydrocarbon chain tails away from water (as shown in the diagram).

  • The oily dirt is collected in centre of the micelle and gets entrapped into it. These micelles stay in water as colloids. Thus, dirt suspended in the micelles is easily rinsed away.

Formation of Micelles

Formation of Micelles

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Question

Write the chemical formula and name of the compound which is the active ingredient of all alcoholic drinks. List its two uses. Write chemical equation and name of the product formed when this compound reacts with - Sodium metal hot concentrated sulphuric acid

Solution

, Ethanol or Ethyl alcohol. It is a good solvent, and also used in medicines.

i)

ii)

Question

An organic compound A is widely used as preservative in pickles and has a molecular formula. The compound reacts with Ethanol to form a sweet smelling compound B.

Identify the compound A

Write the chemical equation for its reaction with ethanol to form compound B.

Which gas is produced when compound A reacts with sodium carbonate?

Name the sweet smelling compound B.

Solution

  • A ¡s Ethanoic Acid,

  • gas is formed

  • The sweet smelling compound B is Ester

Question

How are soaps different from detergents?

What makes water hard?

How ¡s scum formed?

Solution

Soaps Detergents

  • These are sodium or potassium salts of long chain carboxylic acids

  • Soaps are not effective in hard water

  • Soaps form insoluble precipitates with calcium and magnesium ions.

Detergents

  • These are ammonium or sulphonate salts of long chain carboxylic acids.

  • Detergents are effective in hard water

  • They do not form insoluble precipitates with calcium and magnesium ions.

  • The soluble salts of calcium and magnesium make the water hard.

  • Scum is formed by the reaction of calcium or magnesium ions with soap molecules. These ions react with soap molecules forming calcium or magnesium salts of long chain carboxylic acids which are insoluble and precipitate out.