Sunday, June 19, 2022

Class 10 Science | Intext Questions & Answers | Chapter 4 | Carbon and its Compounds

Page: 61


1. What would be the electron dot structure of carbon dioxide which has the formula CO2?

Answer:

2. What would be electron dot structure of sulphur which is made up of eight atoms of sulphur.


Answer:


Page: 68 – 69


1. How many structural isomers can you draw for pentane?


Answer:

Three. They are n-pentane, iso-pentane and neo-pentane.


2. What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?


Answer:

(i) Tetravalency                      (ii) Catenation.

3. What will be the formula and electron dot structure of cyclopentane?

Answer:

Molecular formula: C5 H10.

Electron dot structure:


4. Draw the structures for the following compounds:
(i) Ethanoic acid                      (ii) Bromopentane
(iii) Butanone                           (iv) Hexanal

Answer:

(i) Ethanoic acid (CH3COOH)


(ii) Bromopentane (C5H11Br)


(iii) Butanone (CH3 — CH2 — COCH3)


(iv) Hexanal (C5H11CHO)


5. How would you name the following compounds?



Answer:

(i) Bromoethane
(ii) Methanal
(iii) 1 – Hexyne


Page: 71


1. Why is the conversion of ethanol to ethanoic acid an oxidation reaction?


Answer:

Addition of oxygen to a substance is called oxidation. Here, oxygen is added to ethanol by oxidising agent (alkaline potassium permanganate or acidified potassium dichromate) and it is converted into acid.

2. A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?


Answer:

Burning of ethyne in air produces a sooty flame due to incomplete combustion. It is not enough to melt metals for welding.


Page: 74


1. How would you distinguish experimentally between an alcohol and a carboxylic acid?


Answer:

Test

Alcohol

Carboxylic acid

Litmus test

No change in colour.

Blue litmus solution turns red.

Sodium hydrogen carbonate test

C2H5OH + NaHCO3  No reaction

CH3COOH + NaHCO CH3COONa + H2O + CO2.

Brisk effervescence due to evolution of CO2.


2. What are oxidising agents?


Answer:

Oxidising agents are the substances which give oxygen to another substance or remove hydrogen from a substance. E.g., acidic K2Cr2O7. It oxidises ethanol into ethanoic acid.


Page: 76


1. Would you be able to check if water is hard by using a detergent?


Answer:

No, because detergents can lather well even in hard water. They do not form insoluble calcium or magnesium salts (scum).


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?


Answer:

When the cloth wetted in soap solution is agitated or beaten, the micelles containing oily or greasy dirt get removed from the surface of cloth and go into water.


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