Carbon and its Compounds Class 10 Science

20 Questions | 66 Marks

Explain why carbon forms covalent bonds instead of ionic bonds. 3marks

Define catenation. How does it contribute to the large number of carbon compounds? 2marks

Draw the electron dot structure of ethane (

C_{2} H_{6}

). 2marks

What is the difference between saturated and unsaturated hydrocarbons? Give one example of each. 2marks

Name the functional group present in ethanoic acid. How does it react with sodium carbonate? Write the chemical equation for the reaction. 3marks

What is a homologous series? Give any two characteristics of a homologous series. 2marks

(a) What is observed when ethanol is heated with excess concentrated sulphuric acid at 443 K? Write the balanced chemical equation for the reaction. 2marks(b) What is the role of concentrated sulphuric acid in this reaction? [1 mark]

Explain the formation of micelles when soap is added to water. 3marks

Why are soaps less effective in hard water? What is used as an alternative for cleaning in such cases? 2marks

Distinguish between addition reactions and substitution reactions with examples. 3marks

Name the products formed when ethanol undergoes complete combustion. Write the balanced chemical equation. 2marks

What are structural isomers? Draw the structural isomers of butane (

C_{4} H_{10}

). 3marks

Explain the esterification reaction. Write its chemical equation. 3marks

What are the two characteristic properties of carbon that lead to the formation of a large number of compounds? 2marks

How would you convert ethanol to ethanoic acid? Write the chemical equation for the reaction and name the reagent used. 3marks

Compare the physical and chemical properties of diamond and graphite. 3marks

Assertion (A): Carbon compounds generally have low melting and boiling points.Reason (R): Carbon compounds have weak intermolecular forces.(A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).(B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).(C) Assertion (A) is true, but Reason (R) is false.(D) Assertion (A) is false, but Reason (R) is true. 1mark

Assertion (A): Unsaturated hydrocarbons burn with a yellow, sooty flame.Reason (R): Unsaturated hydrocarbons have a higher percentage of carbon and undergo complete combustion.(A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).(B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).(C) Assertion (A) is true, but Reason (R) is false.(D) Assertion (A) is false, but Reason (R) is true. 1mark

The hydrocarbons with the general formula

C_{n} H_{2 n - 2}

represent:(a) Alkanes(b) Alkenes(c) Alkynes(d) Cycloalkanes 1mark

A carbon compound 'X' is a liquid at room temperature and reacts with sodium metal to produce hydrogen gas. It is also used as a solvent in medicines.(a) Identify 'X'.(b) Write the chemical equation for its reaction with sodium metal.(c) Name the product formed. 3marks

Answers

Carbon has 4 valence electrons. To achieve noble gas configuration, it would need to gain 4 electrons to form

C^{4 -}

or lose 4 electrons to form

C^{4 +}

. Gaining 4 electrons would require a large amount of energy to accommodate the extra electrons in the nucleus with only 6 protons. Losing 4 electrons would also require a large amount of energy to remove them. Therefore, carbon overcomes this problem by sharing its valence electrons with other atoms (of carbon or other elements) to form covalent bonds.

Catenation is the ability of an element to form chains, branches, and rings with itself. Carbon exhibits this property to a great extent due to the strength of the C-C single, double, and triple bonds, its tetravalency, and its small atomic size. This leads to the formation of a vast number of compounds with varying structures and molecular masses.

H H| |H-C-C-H| |H HElectron dot structure:.. ..H : C : C : H.. ..H H

Saturated hydrocarbons contain only single bonds between carbon atoms. They are less reactive. Example: Ethane (

C_{2} H_{6}

).Unsaturated hydrocarbons contain at least one double or triple bond between carbon atoms. They are more reactive. Example: Ethene (

C_{2} H_{4}

) with a double bond, Ethyne (

C_{2} H_{2}

) with a triple bond.

The functional group present in ethanoic acid is the carboxylic acid group (-COOH).Reaction with sodium carbonate:

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}

Carbon dioxide gas is produced, which turns lime water milky. 6. A homologous series is a series of compounds in which the same functional group is present in every member, and the successive members differ by a -CH2- unit. Characteristics: (i) All members have the same functional group. (ii) Successive members differ by a -CH2- unit. (iii) Chemical properties are similar. (iv) Physical properties show a gradual change with increasing molecular mass. 7. (a) When ethanol is heated with excess concentrated sulphuric acid at 443 K, it undergoes dehydration to form ethene.

C H_{3} C H_{2} O H \overset{Conc. H_{2} S O_{4}, 443 K}{\to} C H_{2} = C H_{2} + H_{2} O

(b) Concentrated sulphuric acid acts as a dehydrating agent, removing a molecule of water from ethanol.

Soap molecules have a dual nature: a hydrophilic (water-attracting) ionic head and a hydrophobic (water-repelling) hydrocarbon tail. When soap is added to water, the hydrophobic tails cluster together to form the centre of the micelle, while the hydrophilic heads face outwards towards the water. This arrangement traps oily dirt in the centre, allowing it to be washed away with water.

Soaps are sodium or potassium salts of long-chain carboxylic acids. In hard water, these salts react with calcium and magnesium ions to form insoluble precipitates called scum. This makes the soap less effective.Detergents are used as an alternative because their ionic ends do not form insoluble precipitates with these ions, making them effective in hard water.

Addition reactions involve the addition of another atom or group of atoms across a double or triple bond in an unsaturated hydrocarbon without the loss of any atom. Example: Hydrogenation of vegetable oils.Substitution reactions involve the replacement of one or more hydrogen atoms in a saturated hydrocarbon by other atoms or groups. Example: Reaction of methane with chlorine in the presence of sunlight.

Complete combustion of ethanol produces carbon dioxide and water, releasing heat and light.

C_{2} H_{5} O H + 3 O_{2} \to 2 C O_{2} + 3 H_{2} O

Structural isomers are compounds that have the same molecular formula but different structural arrangements of atoms. Butane (

C_{4} H_{10}

): (i) n-butane:

C H_{3} - C H_{2} - C H_{2} - C H_{3}

(ii) Isobutane (2-methylpropane):

C H_{3} - C H (C H_{3}) - C H_{3}

Propane (

C_{3} H_{8}

) has no structural isomers because there is only one way to arrange three carbon atoms in a chain and satisfy their valencies. 13. Esterification is the reaction between a carboxylic acid and an alcohol in the presence of an acid catalyst (usually concentrated sulphuric acid) to form an ester and water. Example: Reaction of ethanoic acid with ethanol.

C H_{3} C O O H + C H_{3} C H_{2} O H \overset{Acid catalyst}{\to} C H_{3} C O O C H_{2} C H_{3} + H_{2} O

The two characteristic properties of carbon are:(i) Tetravalency: Carbon has four valence electrons, so it can form four covalent bonds.(ii) Catenation: Carbon can form stable bonds with other carbon atoms to form long chains, branched chains, and ring structures.

Ethanol can be converted to ethanoic acid by oxidation. A common oxidizing agent used is acidified potassium dichromate (

K_{2} C r_{2} O_{7}

) or alkaline potassium permanganate (

K M n O_{4}

).Using acidified potassium dichromate:

5 C_{2} H_{5} O H + 4 K_{2} C r_{2} O_{7} + 16 H_{2} S O_{4} \to 5 C H_{3} C O O H + 4 C r_{2} (S O_{4})_{3} + 4 K_{2} S O_{4} + 21 H_{2} O

Or using alkaline potassium permanganate:

5 C_{2} H_{5} O H + 4 K M n O_{4} + 6 H_{2} S O_{4} \to 5 C H_{3} C O O H + 4 M n S O_{4} + 2 K_{2} S O_{4} + 11 H_{2} O

Diamond: Each carbon atom is bonded to four other carbon atoms in a tetrahedral arrangement, forming a rigid three-dimensional structure. It is extremely hard and has a high melting point. It does not conduct electricity.Graphite: Each carbon atom is bonded to three other carbon atoms in a hexagonal planar structure, forming layers. These layers are held together by weak van der Waals forces. It is soft and slippery, and conducts electricity due to the presence of delocalised electrons.

(A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).

(C) Assertion (A) is true, but Reason (R) is false. (Reason is false because unsaturated hydrocarbons undergo incomplete combustion in limited air, leading to a sooty flame; complete combustion in sufficient air gives a clean flame).

(a) 'X' is ethanol (

C_{2} H_{5} O H

).(b) Reaction with sodium metal:

2 C H_{3} C H_{2} O H + 2 N a \to 2 C H_{3} C H_{2} O N a + H_{2}

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Carbon and its Compounds — Important Questions

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