Which reaction of ethanol will decolourise bromine water?

1. $\mathrm{C}_2 \mathrm{H}_5 \mathrm{OH}+\mathrm{HBr} \longrightarrow \mathrm{C}_2 \mathrm{H}_5 \mathrm{Br}+\mathrm{H}_2 \mathrm{O}$
2. $2 \mathrm{C}_2 \mathrm{H}_5 \mathrm{OH} \xrightarrow[413 \mathrm{~K}]{\mathrm{H}^{+}} \mathrm{C}_2 \mathrm{H}_5-\mathrm{O}-\mathrm{C}_2 \mathrm{H}_5+\mathrm{H}_2 \mathrm{O}$
3. $\mathrm{C}_2 \mathrm{H}_5 \mathrm{OH}+\mathrm{Na} \longrightarrow \mathrm{C}_2 \mathrm{H}_5 \mathrm{ONa}+\frac{1}{2} \mathrm{H}_2 \mathrm{O}$
4. $\mathrm{C}_2 \mathrm{H}_5 \mathrm{OH} \xrightarrow[443 \mathrm{~K}]{\mathrm{H}^{+}} \mathrm{C}_2 \mathrm{H}_4+\mathrm{H}_2 \mathrm{O}$

Solution

One of the product in this reaction is ethene, an unsaturated hydrocarbon. It decolourises bromine water. Bromine solution is the classic test for the detection of unsaturation. A few drops of bromine water to the test tube with the ethanol produce reddish-brown colour.

Asked in: AP EAMCET 2021 (25 Aug Shift 1)

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