Class 10 Science Chapter 4 Carbon and its compounds

Chapter 4. Carbon and its Compounds

NCERT Solution for Class 10 Science Chapter 4 Exercise - 1

Question (1)

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

Answer :

Electron dot structure of CO₂

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.)

Answer :

Electron dot structure of a sulphur molecule

Question (3)

How many structural isomers can you draw for pentane?

Answer :

Three structural isomers are possible for pentane.

(i) CH₃-CH₂-CH₂-CH₂-CH₃

(ii)

Ncert solutions for class 10 science chapter 4

(iii)

Question (4)

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

Answer :

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.

Question (5)

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

Answer :

The formula for cyclopentane is C₅H₁₀. Its electron dot structure is given below

Question (6)

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

Answer :

(i)

CH₃COOH,

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

(iii)

CH₃CH₂COCH₃

(iv) CH₃CH₂CH₂CH₂CH₂CHO

Question (7)

How would you name the following compound?

CH₃-XH₂-Br

Answer :

(i) Bromoethane

Question (8)

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

Answer :

CH₃CH₂OH →→ CH₃COOH

Ethanol Ethanoic acid

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?

Answer :

2HC=CH+5O₂ 4CO₂+2H₂O+Heat

When ethyne is burnt in air, it gives a sooty flame. This is due to incomplete combustion caused by the limited supply of air. However, if ethyne is burnt with oxygen, it gives a clean flame with a temperature of 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.

Question (10)

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

Answer :

We can distinguish between an alcohol and a carboxylic acid on the basis of their reaction with carbonates and hydrogen carbonates. The acid reacts with carbonate and hydrogen carbonate to evolve CO₂ gas that turns lime water milky.

Alcohols, on the other hand, do not react with carbonates and hydrogen carbonates

Question (11)

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

Answer :

Detergents are ammonium or sulphonate salts of long chain carboxylic acids. Unlike soap, they do not react with calcium and magnesium ions present in hard water to form scum. They give a good amount of lather irrespective of whether the water is hard or soft. This means that detergents can be used in both soft and hard water. Therefore, it cannot be used to check whether the water is hard or not.

Question (12)

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 :

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 (entrapping the dirt), it is necessary to agitate clothes.

Question (13)

Ethane, with the molecular formula C₂H₆, has
(a) 6 covalent bonds.
(b) 7 covalent bonds.
(c) 8 covalent bonds.
(d) 9 covalent bonds.

Answer :

(b) Ethane has 7 covalent bonds.

Question (14)

Butanone is a four-carbon compound with the functional group
(a) carboxylic acid.
(b) aldehyde.
(c) ketone.
(d) alcohol.

Answer :

(c) The functional group of butanone is ketone.

Question (15)

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.
(c) the fuel is wet.
(d) the fuel is burning completely.

Answer :

(b) While cooking, if the bottom of the vessel is getting blackened on the outside, then it means that the fuel is not burning completely.

Question (16)

Explain the nature of the covalent bond using the bond formation in CH₃Cl.

Answer :

Carbon can neither lose four of its electrons nor gain four electrons as both the processes require extra amount of energy and would make the system unstable. Therefore, it completes its octet by sharing its four electrons with other carbon atoms or with atoms of other elements. The bonds that are formed by sharing electrons are known as covalent bonds. In covalent bonding, both the atoms share the valence electrons, i.e., the shared electrons belong to the valence shells of both the atoms.Here, carbon requires 4 electrons to complete its octet, while each hydrogen atom requires one electron to complete its duplet. Also, chlorine requires an electron to complete the octet. Therefore, all of these share the electrons and as a result, carbon forms 3 bonds with hydrogen and one with chlorine.

Question (17)

Draw the electron dot structures for
(a) ethanoic acid.
(b) H₂S.
(c) propanone.
(d) F₂.

Answer :

(a) Ethanoic acid

(b) H₂S

(c) Propane

(d) F₂

Question (18)

What is a homologous series? Explain with an example

Answer :

A homologous series is a series of carbon compounds that have different numbers of carbon atoms but contain the same functional group. For example, methane, ethane, propane, butane, etc. are all part of the alkane homologous series

The general formula of this series is CnH2n+2.
Methane CH₄
Ethane CH₃CH₃
Propane CH₃CH₂CH₃
Butane CH₃CH₂CH₂CH₃
It can be noticed that there is a difference of −CH₂ unit between each successive compound.

Question (19)

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

Answer :

Ethanol is a liquid at room temperature with a pleasant odour while ethanoic acid has vinegar like smell. The melting point of ethanoic acid is 17°C. This is below room temperature and hence, it freezes during winters.
Ethanoic acid reacts with metal carbonates and metal hydrogen carbonates to form salt, water, and carbon dioxide gas while ethanol does not react with them.

Metal carbonate +Carboxylic acid -->salt water +carbon dioxide

For example, CH₃CH₂OH+Na₂CO₃-->no reaction

Question (20)

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

Answer :

A soap is a sodium or potassium salt of long chain fatty acids. It has one polar end and one non-polar end. The polar end is hydrophilic in nature i.e., this end is attracted towards the water. The non-polar end is hydrophobic but lipophilic, i.e., it is attracted towards hydrocarbons. When soap is added to water, soap molecules arrange themselves in a cluster to keep the non-polar portion out of the water such that the non-polar ends are in the interior of the cluster and the polar ends are on the surface of the cluster. Since the dirt present on clothes is organic in nature and insoluble in water, the hydrophobic ends of the clusters attach themselves to the dirt. This cluster formation in which the dirt is entrapped is the micelle. Micelle formation does not occur in alcohol because the alkyl chain of soap becomes soluble in alcohol.

Question (21)

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

Answer :

Most of the carbon compounds give a lot of heat and light when burnt in air. Saturated hydrocarbons burn with a clean flame and no smoke is produced. The carbon compounds, used as a fuel, have high calorific values. Therefore, carbon and its compounds are used as fuels for most applications.

Question (22)

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

Answer :

Soap does not work properly when the water is hard. A soap is a sodium or potassium salt of long chain fatty acids. Hard water contains salts of calcium and magnesium. When soap is added to hard water, calcium and magnesium ions present in water displace sodium or potassium ions from the soap molecules forming an insoluble substance called scum. A lot of soap is wasted in the process.

Question (23)

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

Answer :

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

Question (24)

What is hydrogenation? What is its industrial application?

Answer :

Hydrogenation is the process of addition of hydrogen. Unsaturated hydrocarbons are added with hydrogen in the presence of palladium and nickel catalysts to give saturated hydrocarbons.

This reaction is applied in the hydrogenation of vegetable oils, which contain long chains of unsaturated carbons.

Question (25)

Which of the following hydrocarbons undergo addition reactions:
C₂H₆, C₃H₈, C₃H₆, C₂H₂ and CH₄.

Answer :

Unsaturated hydrocarbons undergo addition reactions. Being unsaturated
hydrocarbons, C₃H₆ and C₂H₂undergo addition reactions.

Question (26)

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

Answer :

Butter contains saturated fats. Therefore, it cannot be hydrogenated. On the other hand, oil has unsaturated fats. That is why it can be hydrogenated to saturated fats (solids)