# NCERT Class 10: Science-Intext Solutions

Reviewed By:
Krishna Kant Majee
M.Sc., B.Ed.

### Chapter 04-Carbon and its Compounds-Intext Solutions

#### NCERT Book Page Number-61

Q.1. What would be the electron dot structure of carbon dioxide which has the formula $CO_{2}$?
Ans. $CO_{2}$

Q.2. What would be the electron dot structure of a molecule of sulphur which is made up of eight atoms of sulphur $(S_{8})$?
[Hint : The eight atoms of sulphur are joined together in the form of a ring.]
Ans. Sulphur molecule $(S_{8})$ :

#### NCERT Book Page Number-68

Q.1. How many structural isomers can you draw for pentane?
Ans. Three structural isomers are possible for pentane.

Q.2. What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?
Ans. The two features of carbon that give rise to a large number of compounds are as follows :
(i) Catenation : It is the ability to form bonds with other atoms of carbon.
(ii) Tetravalency : With the valency of four, carbon is capable of bonding with four other atoms.

Q.3. What will be the formula and electron dot structure of cyclopentane?
Ans. The formula for cyclopentane is $C_{5}H_{10}$. Its electron dot structure is given below:

Q.4. Draw the structures for the following compounds :
(i) Ethanoic acid (ii) Bromopentane* (iii) Butanone (iv) Hexanal
Are structural isomers possible for bromopentane?
Ans:

(ii) There are many structural isomers possible for bromopentane. Among them, the structures of three isomers are given.

Q.5. How would you name the following compounds?

Ans. (i) Bromoethane (ii) Methanal (common name is formaldehyde) (iii) Hexyne.

#### NCERT Book Page Number -71

Q.1. Why is the conversion of ethanol to ethanoic acid an oxidation reaction?
Ans. $CH_{3}CH_{2}OH + (Alkaline KMnO_{4})\rightarrow CH_{3}COOH$
Since, in this reaction one oxygen is added to ethanol, hence it is an oxidation reaction.
Q.2. A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?
Ans. $2HC ≡ CH + 5O_{2}\rightarrow 4CO_{2} + 2H_{2}O + Heat$
When ethyne is burnt in air, it gives a sooty flame. This is due to incomplete combustion caused by limited supply of air. However, if ethyne is burnt with oxygen, it gives a clean flame with temperature 3000°C because of complete combustion. This oxy-acetylene flame is used for welding. It is not possible to attain such a high temperature without mixing oxygen. This is the reason why a mixture of ethyne and air is not used.

#### NCERT Book Page Number -74

Q.1. How would you distinguish experimentally between an alcohol and a carboxylic acid?
Ans. We can distinguish between an alcohol and a carboxylic acid on the basis of their reaction with carbonates and hydrogen carbonates. Acid reacts with carbonate and hydrogen carbonate to evolve $CO_{2}$ gas that turns lime water milky.
Metal carbonate/Metal hydrogen carbonate + carboxylic acid $rightarrow$ Salt + Water + Carbon dioxide
Alcohols, on the other hand, do not react with carbonates and hydrogen carbonates.

Q.2. What are oxidising agents?
Ans. Oxidising agents are the substances that gain electrons in a redox reaction and whose oxidation number is reduced.

#### NCERT Book Page Number -76

Q.1. Would you be able to check if water is hard by using a detergent?
Ans. Detergent gives lather with hard and soft water both, while a soap gives lather with soft water only. Thus, it is not possible to check if water is hard, by using a detergent.

Q.2. People use a variety of methods to wash clothes. Usually after adding the soap, they ‘beat’ the clothes on a stone, or beat it with a paddle, scrub with a brush or the mixture is agitated in a washing machine. Why is agitation necessary to get clean clothes?
Ans. A soap molecule has two parts namely hydrophobic and hydrophilic. With the help of these, it attaches to the grease or dirt particle and forms a cluster called micelle. These micelles remain suspended as a colloid. To remove these micelles, it is necessary to agitate clothes.