(i) A substance 'X' has the molecular formula C₂H₅OH.
(a) Write the IUPAC name of X.
(b) Write the chemical equation for its dehydration using excess concentrated H₂SO₄ at 443 K. Name the product formed.
(c) What type of reaction is this dehydration — addition, substitution or elimination?
(ii) When X reacts with sodium, a gas Y is produced. Identify Y and write the balanced chemical equation for the reaction.
(iii) State any one industrial or medical use of X.
Generated by claude-sonnet-4-6 · 2026-06-26 01:07 · grounding rag
Model Answer
(i)(a) The IUPAC name of X (C₂H₅OH) is Ethanol.
(i)(b) Dehydration of ethanol with excess conc. H₂SO₄ at 443 K:
$$\text{CH}_3\text{CH}_2\text{OH} \xrightarrow{\text{Hot conc. H}_2\text{SO}_4,\ 443\text{ K}} \text{CH}_2{=}\text{CH}_2 + \text{H}_2\text{O}$$
The product formed is ethene (an unsaturated hydrocarbon).
(i)(c) This dehydration is an elimination reaction (water molecule is eliminated from ethanol).
(ii) When ethanol reacts with sodium, the gas produced is hydrogen (H₂).
$$2\text{Na} + 2\text{CH}_3\text{CH}_2\text{OH} \rightarrow 2\text{CH}_3\text{CH}_2\text{O}^-\text{Na}^+ + \text{H}_2\uparrow$$
(Sodium ethoxide is the other product.)
(iii) Ethanol is used as a solvent in medicines such as tincture iodine, cough syrups, and tonics. / It is also used as an industrial solvent.
Source: Chapter 4, Section 4.4.1 — Properties of Ethanol
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Explanation
- (i)(b): Write the arrow with "Hot conc. H₂SO₄" and temperature above it; examiners check for conditions.
- (i)(c): The textbook calls this a reaction to give an "unsaturated hydrocarbon," but the reaction type is elimination — water is removed from the molecule. State this clearly.
- (ii): The balanced equation must show 2Na and 2C₂H₅OH on the left; one-sided equations lose marks.
- (iii): Any one valid use (medicinal solvent or industrial solvent or fuel additive) is enough for 1 mark — don't write all; it wastes time.
- Keep equations balanced and conditions labelled — these are the two most common mark-losing errors.