Answer the following. (a) Rehmat classified the reaction between Methane and Chlorine in presence of sunlight as a substitution reaction. Support Rehmat's view with suitable justification and illustrate the reaction with the help of a balanced chemical equation. (b) Chlorine gas was prepared using electrolysis of brine solution. Write the chemical equation to represent the change. Identify the other products formed in the process and give one application of each.

(a) Substitution: an H of methane is replaced by Cl; CH_4 + Cl_2 sunlight CH_3Cl + HCl. (b) 2NaCl + 2H_2O → 2NaOH + Cl_2 + H_2; other products NaOH (soaps/detergents) and H_2 (fuel/margarine/ammonia).

ScienceCBSE Class 10 · Sample paper, session 2023-24 · 5 marks · Long answer

CBSE Class 10 Science sample paper 2023-24: question 34(a)

From the official CBSE sample question paper for 2023-24, section D, question 34(a), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q34(a) · 5 marks · Long answerCarbon and its Compounds

Answer the following.

(a)
Rehmat classified the reaction between Methane and Chlorine in presence of sunlight as a substitution reaction. Support Rehmat's view with suitable justification and illustrate the reaction with the help of a balanced chemical equation.
2 marks
(b)
Chlorine gas was prepared using electrolysis of brine solution. Write the chemical equation to represent the change. Identify the other products formed in the process and give one application of each.
3 marks

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2023-24.

Hints

Open one hint at a time and try again before the next.

Hint 1

In the product, what has taken the place of one hydrogen atom of methane?

Hint 2

Brine is aqueous NaCl. Electrolysis gives a gas at each electrode and an alkali remains in solution.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

(a) Rehmat is correct. In this reaction a hydrogen atom of methane is replaced by a chlorine atom. A reaction in which one atom or group is replaced by another is a substitution reaction. Saturated hydrocarbons like methane react this way in sunlight.
1 mark
Balanced equation: $C H_{4} + C l_{2} sunlight C H_{3} Cl + HCl$ (further substitution can give $C H_{2} C l_{2}$ , $CHC l_{3}$ and $CC l_{4}$ ).
1 mark
(b) Electrolysis of brine (chlor-alkali process): $2NaCl (aq) + 2 H_{2} O (l) \to 2NaOH (aq) + C l_{2} (g) + H_{2} (g)$ . Chlorine is released at the anode and hydrogen at the cathode.
1 mark
Other products: sodium hydroxide (NaOH), formed near the cathode, and **hydrogen gas ( $H_{2}$ )**, released at the cathode.
1 mark
Uses (any one each): NaOH is used to make soaps and detergents (also for degreasing metals, paper making, artificial fibres). $H_{2}$ is used as a fuel (also to hydrogenate oils into margarine, and to make ammonia for fertilisers).
1 mark

Answer: (a) Substitution: an H of methane is replaced by Cl; $C H_{4} + C l_{2} sunlight C H_{3} Cl + HCl$ . (b) $2NaCl + 2 H_{2} O \to 2NaOH + C l_{2} + H_{2}$ ; other products NaOH (soaps/detergents) and $H_{2}$ (fuel/margarine/ammonia).

Where the marks are

Justifies substitution: H atom of methane replaced by Cl (1 mark)
Balanced equation $C H_{4} + C l_{2} \to C H_{3} Cl + HCl$ in sunlight (1 mark)
Balanced equation for electrolysis of brine (1 mark)
Identifies NaOH and $H_{2}$ as the other products (1 mark)
One correct use each of NaOH and $H_{2}$ (0.5 + 0.5 marks)

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Chapter: Carbon and its Compounds (notes, formulas, where marks are lost and every past question)

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CBSE Class 10 Science sample paper 2023-24: question 34(a)

Hints

Step-by-step solution

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