Question

(a) (i)Give reason why carbon can neither form C⁴⁺ cations nor C⁴⁻ anions but form covalent compounds.
(ii) What is homologous series of carbon compound? Write the molecular formula of any two consecutive members of homologous series of aldehydes.
(iii) Draw the structure of the molecule of cyclohexane (C₆H₁₂).
OR
(b) (i) Name a commercially important carbon compound having functional group –OH and write its molecular formula. (ii) Write chemical equation to show its reaction with
(1) Sodium metal
(2) Excess conc. sulphuric acid
(3) Ethanoic acid in the presence of an acid catalyst
(4) Acidified potassium dichromate
Also write the name of the product formed in each case.

Answer 1

(a).(i) Carbon has an atomic number of 6 with an electronic configuration of 2, 4. This means:
• To form a C⁴⁺ cation, carbon would need to lose 4 electrons, requiring a large amount of energy to overcome the strong nuclear attraction.
• To form a C⁴⁻ anion, carbon would need to gain 4 electrons, which would cause repulsion between the electrons in the small carbon atom.
Since both processes are energetically unfavorable, carbon forms covalent bonds by sharing electrons to achieve a stable configuration.
(ii) A homologous series is a group of organic compounds having the same general formula, similar chemical properties, and successive members differing by a \(CH_2\)group.
Example: Aldehydes.
- General formula: \(C_nH_{2n+1}CHO\)
- Two consecutive members:
1. Methanal (HCHO) 2. Ethanal (\(CH_3CHO\)).
(iii) Cyclohexane is a cyclic compound with the molecular formula \(C_6H_{12}\). Its structure is represented as follows:

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(b)(i) A commercially important carbon compound with the -OH functional group is Ethanol (C2H5OH). It is widely used as a solvent, in alcoholic beverages, and as a fuel.
(ii) Sodium metal:
Ethanol reacts with sodium metal to produce sodium ethoxide and hydrogen gas.
\[\text{C}_2\text{H}_5\text{OH} + 2\text{Na} \rightarrow 2\text{C}_2\text{H}_5\text{ONa} + \text{H}_2.\]
Product: Sodium ethoxide and hydrogen gas.
Excess conc. sulphuric acid:
Ethanol reacts with excess concentrated sulphuric acid at 170°C to undergo dehydration, forming ethene and water.
\[\text{C}_2\text{H}_5\text{OH} \xrightarrow{\text{Conc. H}_2\text{SO}_4} \text{C}_2\text{H}_4 + \text{H}_2\text{O}.\]
Product: Ethene and water.
Ethanoic acid in the presence of an acid catalyst:
Ethanol reacts with ethanoic acid in the presence of an acid catalyst to form ethyl ethanoate (an ester) and water.
\[\text{C}_2\text{H}_5\text{OH} + \text{CH}_3\text{COOH} \xrightarrow{\text{H}^+} \text{CH}_3\text{COOC}_2\text{H}_5 + \text{H}_2\text{O}.\]
Product: Ethyl ethanoate and water.
Acidified potassium dichromate: 
Ethanol is oxidized by acidified potassium dichromate to form ethanoic acid.
\[\text{C}_2\text{H}_5\text{OH} \xrightarrow{\text{K}_2\text{Cr}_2\text{O}_7/\text{H}^+} \text{CH}_3\text{COOH} + \text{H}_2\text{O}.\]
Product: Ethanoic acid.