NCERT Solutions for Class 10 Science Chapter 4 Carbon and its Compounds

Chapter 4 Carbon and its Compounds Class 10 Science NCERT Solutions will make learning and understanding more easier. NCERT Solutions for Class 10 will definitely useful in improving marks in the board examinations. It will make learning and understanding more easier with detailed and accurate NCERT Solutions. These are essential in developing skills and and helpful in understanding the concepts in better way.

Chapter 4 Carbon and its Compounds Class 10 Science NCERT Solutions

NCERT In Text Questions

Page No: 61

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

Solution

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

Page No: 68

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

Solution

Three structural isomers are possible for pentane.

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

Solution

The two features of carbon that give rise to a large number of compounds are:

(i) Catenation: It is the property of element due to which it forms covalent bonds with other atoms of same element to form chain of atoms.

(ii) Tetravalency: Carbon has valency 4 so it is capable of bonding with 4 other carbon atoms or atoms of other compounds giving rise to compounds with specific properties depending on the elements present in the compound.

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

Solution

The formula for cyclopentane is C₅H₁₀.

Page No: 69

4. Draw the structures for the following compounds.

(i) Ethanoic acid

(ii) Bromopentane*

(iii) Butanone

(iv) Hexanal

*Are structural isomers possible for bromopentane?

Solution

(i) Ethanoic acid

(ii) There are many structural isomers possible for bromopentane.

(iii) Butanone

(iv) Hexanal

5. How would you name the following compounds?

Solution

(i) Bromoethane

(ii) Methanal (formaldehyde)

(iii) Hexyne

Page No: 71

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

Solution

The conversion of ethanol to ethanoic acid is an oxidation reaction because it involves addition of oxygen to alcohol (ethanol) to convert it to ethanoic acid.

CH₃CH₂OH + (Alkaline KMnO₄) → CH₃COOH

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

Solution

On combustion in air, ethyne  produces a yellow flame with lots of black smoke. Due to this incomplete combustion, heat produced is low and temperature obtained is also low. For welding purposes, high temperature (3000° C) is required. When a mixture of ethyne and oxygen is used, complete combustion is achieved and very high temperature required for welding is obtained. Hence, a mixture of ethyne and oxygen is used for welding instead of a mixture of ethyne and air.

2HC ≡ CH + 5O₂ → 4CO₂ + 2H₂O + Heat

Page No: 74

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

Solution

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 CO2 gas that turns lime water milky.

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

2. What are oxidising agents?

Solution

The substances which can oxidise other substances by providing oxygen are called oxidising agents.

Page No: 76

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

Solution

Detergents are ammonium or sulphonate salts of long chain carboxylic acids. 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.

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?

Solution

A soap molecule has two ends-one-end are hydrophobic and the others end is 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.

Page No: 77

Exercise

1. Ethane, with the molecular formula C₂H₆ has

(a) 6 covalent bonds.

(b) 7 covalent bonds.

(c) 8 covalent bonds.

(d) 9 covalent bonds.

Solution

(b) 7 covalent bonds.

2. Butanone is a four-carbon compound with the functional group

(a) carboxylic acid.

(b) aldehyde.

(c) ketone.

(d) alcohol.

Solution

(c) ketone.

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.

(c) the fuel is wet.

(d) the fuel is burning completely.

Solution

(b) the fuel is not burning completely.

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

Solution

In chloromethane (CH₃Cl), carbon atom has four valence electrons (Z=6; i.e., 2, 4) whereas each hydrogen atom has 1 electron (Z= 1), chlorine atom have 7 valence electron (Z=17, i.e., 2, 8, 7). In order to complete their octet, carbon shares its three valence electrons with three hydrogen atoms and one of its valence electron with chlorine atom. Since, bonds are formed because of sharing of electrons, hence these are covalent bonds.

The structure of CH3Cl is given below:

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

Solution

(a) ethanoic acid.

(b) H₂S

(c) propanone.

(d) F₂.

6. What is a homologous series? Explain with an example.

Solution

Homologous series is a series of compounds which have same functional group but have different number of carbon atoms.

For example, methane, ethane, propane, butane, etc. are all part of the alkane homologous series. The general formula of this series is C_nH_2n+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.

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

Solution

Physical Properties:

• Smell: Ethanol has a pleasant smell whereas ethanoic acid has a pungent smell.

• Taste: Ethanol has a burning taste whereas ethanoic acid has a sour taste.

• Boiling points: The boiling point of ethanol is low whereas that of ethanoic acid is comparatively high.

Chemical Properties:

• Action on litmus: Ethanol has no action on any litmus (so it is a neutral compound) but ethanoic acid turns blue litmus to red (so it is an acidic compound).

• Action on sodium hydrogencarbonate: Ethanol has no reaction with sodium hydrogencarbonate but ethanoic acid gives brisk effervescence of carbon dioxide with sodium hydrogencarbonate.

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

The micelle formation takes place when soap is added to water because the hydrocarbon chains of soap molecules are hydrophobic (water repelling) which are insoluble in water but the ionic ends of the soap molecules are hydrophilic (water attracting) and hence soluble in water. In a soap micelle, the uncharged ends of the hydrocarbon chains are on the inside whereas the charged ionic ends are on the outside.

No, micelle formation will not be possible in ethanol because the alkyl chain of soap becomes soluble in alcohol. Ethanol is not as polar as soap, so micelles is not formed in other solvents such as ethanol.

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

Solution

Carbon and its compounds are used as fuels for most applications because they produce a large amount of heat and light, when burnt in air. Saturated hydrocarbons burn with clean flame and no smoke is produced.

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

Solution

Hard water contains calcium and magnesium salts. When soap is treated with hard water, then the calcium and magnesium ions of hard water react with soap to form an insoluble precipitate called 'scum'. The scum is formed because the calcium and magnesium salts of soap are insoluble in water.

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

Solution

Soap solution is basic in nature so it will turn red litmus paper to blue but it will have no effect on blue litmus paper.

12. What is hydrogenation? What is its industrial application?

Solution

Unsaturated hydrocarbons undergo addition reaction with hydrogen in presence of catalysts like Pd, Pt or Ni, such a process is known as hydrogenation.

This reaction is used for the hydrogenation of vegetable oil into vanaspati ghee.

13. Which of the following hydrocarbons undergo addition reactions:

C_2, H₆, C₃H₈, C₃H₆, C₂H₂ and CH₄.

Solution

Unsaturated hydrocarbons undergo addition reactions. Being unsaturated hydrocarbons, C₃H₆ and C₂H₂ undergo addition reactions.

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

Solution

Cooking oil is unsaturated hydrocarbon whereas butter is saturated hydrocarbon. We know that brown colour of bromine disappears when a drop of bromine is added to an unsaturated compound whereas there is no reaction between saturated hydrocarbons and bromine. Thus, when a drop of bromine is added to cooking oil, its colour disappears whereas when a drop of bromine is added to butter, it becomes brown.

15. Explain the mechanism of the cleaning action of soaps.

Solution

Soaps contain two parts, a large hydrocarbon which is a hydrophobic (water repelling) and a negative charged head, which is hydrophillic (water attracting). When a soap or detergent is dissolved in water the molecule gather together as clusters, called micelles. The tails stick inwards and the head outwards. The hydrocarbon tail attaches itself to oily dirt. When water is agitated, the oily dirt tends to lift off from the dirty surface and dissociates into fragments. The solution now contains small globules of oil surrounded by detergent molecules. The negatively charged heads present in water prevent the small globules from coming together and form aggregates. Thus, the oily dirt is removed from the object.

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