Science — CBSE Class 10 board question

(i) Two isomeric structures of Butene (C₄H₈):

But-1-ene:
$$\text{CH}_2 = \text{CH} - \text{CH}_2 - \text{CH}_3$$

But-2-ene:
$$\text{CH}_3 - \text{CH} = \text{CH} - \text{CH}_3$$

---

(ii) Names of compounds:

(I) CH₃–CH₂–CH₂Cl → 1-Chloropropane

(II) CH₃–CO–CH₂–CH₃ → Butanone

---

(iii) Chemical equations with conditions:

(I) Complete oxidation of ethanol:
$$\text{CH}_3\text{CH}_2\text{OH} + 3\text{O}_2 \rightarrow 2\text{CO}_2 + 3\text{H}_2\text{O} + \text{heat and light}$$
Condition: Sufficient supply of oxygen (excess O₂).

(II) Hydrogenation of propene:
$$\text{CH}_3 - \text{CH} = \text{CH}_2 + \text{H}_2 \xrightarrow{\text{Ni catalyst}} \text{CH}_3 - \text{CH}_2 - \text{CH}_3$$
Condition: Nickel (Ni) catalyst.

(III) Ethanoic acid reacts with ethanol (Esterification):
$$\text{CH}_3\text{COOH} + \text{C}_2\text{H}_5\text{OH} \underset{\Delta}{\overset{\text{conc. H}_2\text{SO}_4}{\rightleftharpoons}} \text{CH}_3\text{COOC}_2\text{H}_5 + \text{H}_2\text{O}$$
Condition: Concentrated H₂SO₄ as catalyst and heat (Δ).

Source: Chapter 4 — Carbon and its Compounds, Sections 4.2.5, 4.3.1, 4.3.3

---

• (i) Isomers of butene differ by position of the double bond. But-1-ene and but-2-ene are the most expected answers. A third isomer (2-methylpropene) is also valid but two are enough for 2 marks.
• (ii) Use Table 4.4 rules: Cl at end = chloro- prefix; 4-carbon ketone = butanone (drop 'e' from butane + one).
• (iii) Always balance combustion equations. Hydrogenation requires Ni catalyst — this is a standard condition examiners expect. Esterification needs both conc. H₂SO₄ and heat, and the reversible arrow (⇌) is important. Missing the condition loses a mark.