Lesson: Carbon and its Compounds

Question: 1

Ethane, with the molecular formula $C_{2} H_{6}$ has:

(a) 6 covalent bonds.

(b) 7 covalent bonds.

(d) 9 covalent bonds.

Solution:

Question:2

Butanone is a four-carbon compound with the functional group:

(a) Carboxylic acid

(b) Aldehyde

(d) Alcohol

Solution:

Question:3

While cooking, if the bottom of the vessel is getting blackened on the outside, it means that:

(a) The food is not cooked completely.

(b) The fuel is not burning completely.

(d) The fuel is burning completely.

Solution:

Question:4

Explain the nature of the covalent bond using the bond formation in $C H_{3} C l$ .

Solution:

The structure of $C H_{3} C l$ is given below.

Carbon has four valence electrons. In order to form an octet, it needs four more electrons. It shares 1 electron each with 3 hydrogen atoms and 1 electron with chlorine atom. In this way, chlorine and the three hydrogen atoms attain a stable configuration. Since these bonds are formed because of sharing of electrons, these are therefore called covalent bonds.

Question:5

Draw the electron dot structures for:

(a) Ethanoic acid

(b) $H_{2} S$

(d) $F_{2}$

Solution:

Question:6

What is a homologous series? Explain with an example.

Solution:

A series of carbon compounds is said to be homologous when difference between two successive compounds is $C H_{2}$ .

Example: Methane, ethane, propane, butane, etc. belong to the alkane homologous series. The general formula of this series is $C_{n} H_{2 n + 2}$ .

Formula of methane: $C H_{4}$

Formula of ethane: $C H_{3} C H_{3}$

Formula of propane: $C H_{3} C H_{2} C H_{3}$

Formula of butane: $C H_{3} C H_{2} C H_{2} C H_{3}$

Here, there is a difference of $C H_{2}$ unit between two successive compounds.

Question:7

How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?

Solution:

Ethanol and Ethanoic acid can be differentiated on the basis of their following properties:

Ethanol	Ethanoic acid
Physical Properties:
It has a pleasant smell.	It has a pungent vinegar-like smell.
It does not freeze in winter	It freezes in winter.
Chemical Properties:
It does not react with metal carbonates.	It reacts with metal carbonates.
It does not react with NaOH.	It reacts with NaOH.

Question: 8

Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?

Solution:

A soap molecule has two ends. One end is hydrophilic and the other end is hydrophobic. When soap is dissolved in water and clothes are put in the solution, soap molecules arrange themselves in a cluster. In this, the hydrophilic end is outside the sphere and hydrophobic end is towards the centre of the sphere.

The dirt present in the clothes is insoluble in water. The hydrophobic ends of the clusters attach themselves to the dirt. This cluster formation in which the dirt is entrapped is called micelle.

Micelles will not be formed in ethanol as it is not as polar as soap.

Question:9

Why is carbon and its compounds used as fuels for most applications?

Solution:

Carbon and its compounds are used as fuel as they have large number of carbon and hydrogen. When burnt in the presence of air, they give a large amount of heat as they have high calorific value. Therefore, carbon and its compounds are used as fuels for most applications.

Question: 10

Explain the formation of scum when hard water is treated with soap.

Solution:

Hard water contains salts of calcium and magnesium. When it is treated with soap, the soap molecules react with these salts and form a precipitate. This precipitate is called scum. A large amount of soap is wasted in the formation of scum before it is used to wash clothes. This makes soap unsuitable to wash clothes in hard water.

Question: 11

What change will you observe if you test soap with litmus paper (red and blue)?

Solution:

Soap is basic in nature. So, it will turn red litmus blue. However, the colour of blue litmus will remain blue.

Question: 12

What is hydrogenation? What is its industrial application?

Solution:

The addition of hydrogen to an unsaturated hydrocarbon to obtain saturated hydrocarbon is called hydrogenation. This reaction is carried out in the presence of catalysts like nickel or palladium.

Industrial application:

· In petrochemical industries, hydrogenation is used to convert alkenes into alkanes (paraffins) and cycloalkanes.

· It is also used to prepare vegetable ghee from vegetable oils.

Question: 13

Which of the following hydrocarbons undergo addition reactions?

$C_{2} H_{6}, C_{3} H_{8}, C_{3} H_{6}, C_{2} H_{2} a n d C H_{4}$ .

Solution:

$C_{3} H_{6} a n d C_{2} H_{2}$ are unsaturated hydrocarbons. Unsaturated hydrocarbons undergo addition reactions.

Question: 14

Give a test that can be used to differentiate chemically between butter and cooking oil.

Solution:

Butter contains saturated fat while cooking oil has unsaturated fat. All unsaturated carbon compounds decolorize bromine water whereas saturated hydrocarbons do not decolorize bromine water. So, bromine water test can be applied to differentiate between butter and cooking oil.

Question: 15

Explain the mechanism of the cleaning action of soaps.

Solution:

Soap molecules have two ends. One end is hydrophilic and another end is hydrophobic. When soap is dissolved in water, the soap molecules arrange themselves in a cluster. Since the dirt present in the clothes is insoluble in water, the hydrophobic ends of the clusters attach themselves to the dirt. The dirt is entrapped in the cluster. This cluster formation in which the dirt is entrapped is called micelle. These micelles remain suspended in the water. When rinsed, the dirt particles are washed away with water.