The table given below shows the hints given by the quiz master in a quiz. S.NO HINT --- --- (i) Substance 'C' is used as a preservative. (ii) 'C' has two carbon atoms; 'C' is obtained by the reaction of 'A' in presence of alkaline Potassium permanganate followed by acidification. (iii) Misuse of 'A' in industries is prevented by adding Methanol, Benzene, and pyridine to 'A'. (iv) 'F' is formed on heating 'A' in presence of conc Sulphuric acid. (v) 'F' reacts with Hydrogen gas in presence of Nickel and Palladium catalyst. Based on the above hints answer the following questions. (a) Give the IUPAC names of A and F. (b) Illustrate with the help of chemical equations the changes taking place. (A → C and A → F) (b) Name the chemical reactions which occur in steps 2 and 5. Identify the compounds formed in these steps if 'A' is replaced with its next homologue.

ScienceCBSE Class 10 · Sample paper, session 2023-24 · 4 marks · Case-based

CBSE Class 10 Science sample paper 2023-24: question 37

From the official CBSE sample question paper for 2023-24, section E, question 37, for 4 marks. Try it first; the hints and our step-by-step solution are below.

Q37 · 4 marks · Case-basedCompetency-basedCarbon and its Compounds

The table given below shows the hints given by the quiz master in a quiz.

S.NO	HINT
(i)	Substance 'C' is used as a preservative.
(ii)	'C' has two carbon atoms; 'C' is obtained by the reaction of 'A' in presence of alkaline Potassium permanganate followed by acidification.
(iii)	Misuse of 'A' in industries is prevented by adding Methanol, Benzene, and pyridine to 'A'.
(iv)	'F' is formed on heating 'A' in presence of conc Sulphuric acid.
(v)	'F' reacts with Hydrogen gas in presence of Nickel and Palladium catalyst.

Based on the above hints answer the following questions.

(a)
Give the IUPAC names of A and F.
1 mark
(b)
Illustrate with the help of chemical equations the changes taking place. ( $A \to C$ and $A \to F$ )
3 marks
(b)
Name the chemical reactions which occur in steps 2 and 5. Identify the compounds formed in these steps if 'A' is replaced with its next homologue.
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

A two-carbon acid used as a preservative is found in vinegar. Which alcohol is oxidised to it?

Hint 2

Heating an alcohol with conc. sulphuric acid removes water. Which hydrocarbon forms, and why does it react with hydrogen?

Hint 3

For the next homologue, add one $- C H_{2} -$ unit to each compound.

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.

Reasoning from the hints: C has two carbon atoms and is used as a preservative (in pickles), so C is ethanoic acid. A is oxidised to C, and A is denatured with methanol, benzene and pyridine to stop its misuse, so A is ethanol. Heating A with conc. $H_{2} S O_{4}$ dehydrates it to F, which takes up hydrogen, so F is an alkene, ethene.
(a) IUPAC names: A = ethanol ( $C H_{3} C H_{2} OH$ ); F = ethene ( $C H_{2} = C H_{2}$ ).
1 mark
(b) $A \to C$ (oxidation):
$C H_{3} C H_{2} OH alkaline KMn O_{4} + heat C H_{3} CO O^{-} (salt) H^{+} C H_{3} COOH$
Ethanol is oxidised to ethanoate in the alkaline medium. Acidification gives ethanoic acid (C).
1½ marks
(b) $A \to F$ (dehydration):
$C H_{3} C H_{2} OH hot conc. H_{2} S O_{4}, 443 K C H_{2} = C H_{2} + H_{2} O$
Conc. $H_{2} S O_{4}$ acts as a dehydrating agent.
1½ marks
(b) Alternative, part 1: Step 2 (ethanol to ethanoic acid) is an oxidation reaction. Step 5 (ethene + $H_{2}$ with Ni/Pd catalyst) is an addition reaction (hydrogenation).
1 mark
(b) Alternative, part 2: The next homologue of ethanol is propanol, $C H_{3} C H_{2} C H_{2} OH$ .
- Step 2: $C H_{3} C H_{2} C H_{2} OH alk. KMn O_{4}, H^{+} C H_{3} C H_{2} COOH$ gives propanoic acid.
1 mark
- Step 5: propanol dehydrates (step 4) to propene, $C H_{3} CH = C H_{2}$ . Hydrogenation then gives propane:
$C H_{3} CH = C H_{2} + H_{2} Ni/Pd C H_{3} C H_{2} C H_{3}$
1 mark

Answer: (a) A = ethanol, F = ethene. (b) $C H_{3} C H_{2} OH \to C H_{3} COOH$ (alk. $KMn O_{4}$ , then $H^{+}$ ); $C H_{3} C H_{2} OH \to C H_{2} = C H_{2} + H_{2} O$ (hot conc. $H_{2} S O_{4}$ ). OR (b): step 2 oxidation, step 5 addition (hydrogenation). With propanol, step 2 gives propanoic acid; propanol gives propene, which is hydrogenated in step 5 to propane.

Where the marks are

Names A as ethanol and F as ethene (1 mark)
Correct equation for oxidation of ethanol to ethanoic acid using alkaline $KMn O_{4}$ followed by acidification (1.5 marks)
Correct equation for dehydration of ethanol to ethene with hot conc. $H_{2} S O_{4}$ (1.5 marks)
OR: names step 2 as oxidation and step 5 as addition/hydrogenation (1 mark)
OR: identifies the compounds for the next homologue, propanol: propanoic acid in step 2 (1 mark)
OR: propene, hydrogenated to propane in step 5 (1 mark)

Revise the chapter

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

Practise this chapterBoard-style questions from Carbon and its Compounds, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2023-24: every question, by section.

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CBSE Class 10 Science sample paper 2023-24: question 37

Hints

Step-by-step solution

Revise the chapter

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