Cls 10 sci chp 4 soln

 Class 10 Science 

 Chapter 4 Carbon and its Compounds 

 Solutions 

Intext Questions 

Page Number: 61

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

Ans:

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

Ans:

Page Number: 68 – 69

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

Ans:

Three, these 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 ?

Ans:

(i) Tetravalency

(ii) Catenation.

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

Ans:

The molecular formula of cyclopentane is C5 H10 .

The electron dot structure of cyclopentane is.

4. Draw the structures for the following compounds :

(i) Ethanoic acid

(ii) Bromopentane

(iii) Butanone

(iv) Hexanal

Ans:

(i) Ethanoic acid (CH3COOH)

(ii) Bromopentane (C5H11Br)

(iii) Butanone (CH3 — CH2 — COCH3)

(iv) Hexanal (C5H11CHO)

5. How would you name the following compounds ?

Ans:

(i) Bromoethane

(ii) Methanal

(iii) 1 – Hexyne

Page Number: 71

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

Ans:

Conversion of ethanol into ethanoic acid is an oxidation reaction because addition of oxygen to a substance is called oxidation. Here, oxygen is added to ethanol by oxidising agent like 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 ?

Ans:

A mixture of ethyne and air is not used for welding because burning of ethyne in air produces a sooty flame due to incomplete combustion, which is not enough to melt metals for welding.

Page Number: 74

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

Ans:

Acid reacts with carbonate and hydrogen carbonate to evolve CO2 gas that turns lime water milky.

2CH3COOH + Na2CO3 → 2CH3COONa + H2O + CO2

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

2. What are oxidising agents ?

Ans:

Oxidising agents are the substances which give oxygen to another substances or which remove hydrogen from a substance.

Page Number: 76

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

Ans:

Detergent gives lather with hard and soft water both, while a soap gives lather with soft water only. Thus, it is not possible to check if water is hard; by using a detergent.

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 ?

Ans:

It is necessary to agitate to get clean clothes because the soap micelles which entrap oily or greasy particles on the surface of dirty cloth have to be removed from its surface.

Exercise questions

1. Ethane, with the molecular formula C2H6 has

(a) 6 covalent bonds

(b) 7 covalent bonds

c) 8 covalent bonds

(d) 9 covalent bonds

Ans: (b) 7 covalent bonds.

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

(a) carboxylic acid

(b) aldehyde

c) ketone

(d) alcohol

Ans: 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.

Ans: (b) The fuel is not burning completely.

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

Ans:

Carbon has four valence electrons. It shares 1 electron each with 3 hydrogen atoms and 1 electron with chlorine. The bond between C and Cl atoms is covalent but due to higher value of electro-negativity of Cl, the C–Cl bond is polar in nature.

5. Draw the electron dot structures for

(a) ethanoic acid

(b) propanone

c) H2S

(d) F2.

Ans:

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

Ans:

A homologous series is a group of organic compounds having in which the successive compounds differ by -CH2 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.

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

Ans:

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

Ans:

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 soap molecules are hydrophilic (water attracting) and hence soluble in water.

Such micelle formation will not be possible in other solvents like ethanol in which sodium salt of fatty acids do not dissolve.

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

Ans:

Carbon and its compounds give a large amount of heat per unit weight. therefore, used as fuels for most applications.

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

Ans:

Hard water contains salts of calcium and magnesium. Calcium and magnesium on reacting with soap form insoluble precipitate called scum. The scum formation lessens the cleansing property of soaps in hard water.

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

Ans:

Red litmus will turn blue because soap is alkaline in nature. Blue litmus remains blue in soap solution.

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

Ans:

The addition of hydrogen to an unsaturated hydrocarbon to obtain a saturated hydro-carbon is called hydrogenation. The process of hydrogenation takes place in the presence of nickel (Ni) or palladium (Pd) metals as catalyst.

Application : The process of hydrogenation has an important industrial application. It is used to prepare vegetable ghee (or vanaspati ghee) from vegetable oils.

13. Which of the following hydrocarbons undergo addition reactions :

C2H6, C3H8, C3H6, C2H2 and CH4

Ans:

Addition reactions take place only in unsaturated hydrocarbons. So addition reaction take place only in C3H6 and C2H2.

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

Ans:

we can distinguish chemically between a cooking oil and butter by the bromine water. Add bromine water to a little of cooking oil and butter taken in separate test-tubes.

> Cooking oil decolourises bromine water showing that it is an unsaturated compound.

> Butter does not decolourise bromine water showing that it is a saturated compound.

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

Ans:

> The molecules of soap are sodium or potassium salts of long chain carboxylic acids.

> The ionic end of soap interacts with water while the carbon chain interacts with oil.

> The soap molecules thus form structure called micells. This forms an emulsion in water.

> The soap micelles thus helps in pulling out the dirt in water and we can wash our clothes clean.