(i) When sodium is dropped in ethanol, it reacts vigorously to produce sodium ethoxide and hydrogen gas is evolved.
$$2\text{Na} + 2\text{CH}_3\text{CH}_2\text{OH} \rightarrow 2\text{CH}_3\text{CH}_2\text{O}^-\text{Na}^+ + \text{H}_2\uparrow$$
(ii) The melting point of pure ethanoic acid is 290 K. Therefore it often freezes (solidifies) during winter in cold climates, giving it an ice-like appearance. This is why it is called glacial acetic acid.
(iii) When ethanol is heated at 443 K with excess conc. H₂SO₄, it undergoes dehydration to form ethene (an unsaturated hydrocarbon) and water.
$$\text{CH}_3\text{CH}_2\text{OH} \xrightarrow{\text{Hot conc. H}_2\text{SO}_4,\ 443\text{K}} \text{CH}_2{=}\text{CH}_2 + \text{H}_2\text{O}$$
Conc. H₂SO₄ acts as a dehydrating agent — it removes water from ethanol.
(iv) Saponification is the hydrolysis of an ester by an alkali (NaOH) to give back alcohol and the sodium salt of the carboxylic acid.
$$\text{CH}_3\text{COOC}_2\text{H}_5 + \text{NaOH} \rightarrow \text{C}_2\text{H}_5\text{OH} + \text{CH}_3\text{COONa}$$
Source: Chapter 4, Sections 4.4.1 and 4.4.2
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