Lesson: Carbon and its Compounds

Question:1

What would be the electron dot structure of carbon dioxide which has the formula $C O_{2}$ ?

Solution:

Question:2

What would be the electron dot structure of a molecule of sulphur which is made up of eight atoms of sulphur?

(Hint $-$ The eight atoms of sulphur are joined together in the form of a ring.)

Solution:

Question:3

How many structural isomers can you draw for pentane?

Solution:

Question:4

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

Solution:

The following are the features due to which carbon atoms can form a large number of compounds:

· Catenation $-$ Carbon can form bond with other carbon atoms.

· Tetravalency $-$ The valency of carbon is four. It means that one carbon atom can form bonds with four different atoms. Even if one of these four atoms is changed, a new compound is formed.

Question:5

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

Solution:

The formula of cyclopentane is $C_{5} H_{10}$ .

Question: 6

Draw the structures for the following compounds.

(a) Ethanoic acid

(b) Bromopentane*

(d) Hexanal.

*Are structural isomers possible for bromopentane?

Solution:

Question: 7

How would you name the following compounds?

Solution:

(i) Bromoethane

(ii) Methanal (formaldehyde)

(iii) Hexyne

Question: 8

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

Solution:

$C H_{3} C H_{2} O H + 2 [O] \overset{A l k a l i n e K M n O_{4}}{\to} C H_{3} C O O H + H_{2} O$

In this reaction, one oxygen atom is added to ethanol to form ethanoic acid. Hence, it is an oxidation reaction.

Question: 9

A mixture of oxygen and ethyne is burnt for welding.

Can you tell why a mixture of ethyne and air is not used?

Solution:

When a mixture of oxygen and ethyne is burnt for welding, the following reaction takes place:

$2 C_{2} H_{2} + 5 O_{2} \to 4 C O_{2} + 2 H_{2} O + H e a t$

Due to the presence of oxygen, complete combustion takes place.

The air, however, contains limited supply of oxygen. So, when ethyne is burnt in air, it results in incomplete combustion.

Question: 10

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

Solution:

An alcohol and a carboxylic acid can be distinguished on the basis of their reaction with carbonates and hydrogen carbonates.

On reacting with an acid, a carbonate or a hydrogen carbonate give $C O_{2}$ . $C O_{2}$ gas turns lime water milky.

$\begin{array}{l} 2 C H_{3} C O O H + N a_{2} C O_{3} \to 2 C H_{3} C O O N a + H_{2} O + C O_{2} \\ C H_{3} C O O H + N a H C O_{3} \to C H_{3} C O O N a + H_{2} O + C O_{2} \end{array}$

An alcohol, however, does not react with carbonates and hydrogen carbonates.

Question: 11

What are oxidising agents?

Solution:

The substances that give oxygen or replace hydrogen in a chemical reaction are called oxidising agents.

Question: 12

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

Solution:

No, it is not possible to check if water is hard by using detergent as detergents form lather with both hard and soft water.

Question: 13

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?

Solution:

One end of a soap molecule is hydrophobic and the other is hydrophilic. The hydrophobic end attaches to the dirt particles and forms a cluster called micelle.

The hydrophilic end remains attached to water.

When the cloth is agitated, these micelles get dispersed in water due to which the soap water becomes dirty and the clothes get cleaned.