Q1. [4] § 4.2.3 Will you be my Friend? § 4.2.5 Nomenclature of Carbon Compounds § 4.3.2 Oxidation
More than three million carbon compounds have been discovered in the field of chemistry. The diversity of these compounds is due to the capacity of carbon atoms for bonding with one another as well as with other atoms. Most of the carbon compounds are poor conductors of electricity and have low melting and boiling points.
Read the source and answer the sub-parts that follow.
- (a) Write the molecular formula of first two members of homologous series having functional group –Br. [1]
- (b) Given below are the formulae of some functional groups : (i) –C(=O)H (an aldehyde group, –CHO), (ii) –C(=O)– (a carbonyl/ketone group, >C=O). Write the name of these functional groups. [1]
- (c) What would be observed on adding a 5% alkaline potassium permanganate drop by drop to some warm ethanol taken in a test tube ? State the role of KMnO₄ in the reaction and write the chemical equation for the reaction involved. [2]
Previously asked in CBSE board exam
2024 31/3/1 Q37
Generated by claude-sonnet-4-6 · 2026-06-15 06:50 · grounding stimulus
Model Answer
(a) The first two members of the homologous series with functional group –Br (haloalkanes) are:
- CH₃Br (Bromomethane)
- C₂H₅Br (Bromoethane)
(b)
(i) –CHO → Aldehyde group
(ii) >C=O → Ketone (Carbonyl) group
(c) Observation: The pink/purple colour of alkaline KMnO₄ is decolourised.
Role of KMnO₄: It acts as an oxidising agent.
Chemical Equation:
$$\text{CH}_3\text{CH}_2\text{OH} \xrightarrow{\text{Alkaline KMnO}_4, \Delta} \text{CH}_3\text{COOH}$$
Ethanol is oxidised to ethanoic acid (acetic acid).
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Explanation
- (a) The –Br functional group series is called haloalkanes. Just replace –H of alkane with –Br; first member = CH₃Br, second = C₂H₅Br.
- (b) These are standard functional group names from the NCERT table — must be memorised exactly.
- (c) Examiners expect three things: observation (decolourisation), role (oxidising agent), and the balanced/word equation. KMnO₄ oxidises ethanol → ethanoic acid; this is a key reaction in the Carbon chapter.
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