Carbon and Its Compounds

NCERT Exemplar Problems

Short Answer Part 1

A compound X is formed by the reaction of a carboxylic acid C₂H₄O₂ and an alcohol in presence of a few drops of H₂SO₄. The alcohol on oxidation with alkaline KMnO₄ followed by acidification gives the same carboxylic acid as used in this reaction. Give the names and structures of (a) carboxylic acid, (b) alcohol and (c) the compound X. Also write the reaction.

Answer: The carboxylic acid is ethanoic acid, the alcohol is ethyl alcohol and compound X is ester. The reaction is as follows:

CH₃COOH + CH₃ → CH₃COOCH₂CH₃

Why detergents are better cleansing agents than soaps? Explain.

Answer: Soaps can work properly only in soft water but not in hard water. This happens because soap forms precipitate after reacting with magnesium and calcium salts which are present in hard water. But detergents work equally good in soft water and hard water because they do not form precipitate even in hard water. Hence, detergents are better cleansing agents than soaps.

Write the names of the following compounds

Answer: Pentaoic acid

Answer: Butyne

Answer: Heptanal

Answer: Pentanol

Draw the electron dot structure of ethyne and also draw its structural formula

Answer:

Identify and name the functional groups present in the following compounds.

Answer: Hydroxyl

Answer: Carboxylic acid

Answer: Ketone

Answer: Alkene

Name the functional groups present in the following compounds

1. CH₃COCH₂CH₂CH₂CH₃
   
   Answer: Ketone
2. CH₃CH₂CH₂COOH
   
   Answer: Carboxylic acid
3. CH₃CH₂CH₂CH₂CHO
   
   Answer: Aldehyde
4. CH₃CH₂OH
   
   Answer: Alcohol

How is ethene prepared from ethanol? Give the reaction involved in it.

Answer: When ethanol is heated with excess of concentrated sulphuric acid at 443 K; it produces ethene. Hydrolysis of ethanol is involved in this reaction. This can be shown by following equation.

CH₃CH₂OH + hot conc. H₂SO₄ at 443 K → H₂C=CH₂ + H₂

Intake of small quantity of methanol can be lethal. Comment.

Answer: Methanol gets oxidized into methanal when it goes to the liver. Methanal results in coagulation of the protoplasm of cells. Moreover, it also affects the optic nerve and causes blindness. These effects of methanol make it lethal.

A gas is evolved when ethanol reacts with sodium. Name the gas evolved and also write the balanced chemical equation of the reaction involved.

Answer: Hydrogen gas is evolved in this reaction. This reaction can be shown by following equation.

2CH₃CH₂OH + 2Na → 2CH₃CH₂ONa + H₂