What is the product Y in the following chemical reaction?
\( \displaystyle \ce{H3C-CH2-OH} \xrightarrow[443\ \mathrm{K}]{\ce{H2SO4}} \text{Y} \)
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → H2C=CH2
Alcohols lose a molecule of water when heated with concentrated sulphuric acid (acidic dehydration). The product depends on the temperature:
At 443 K, with excess acid, water is lost from within one molecule (intramolecular elimination) and an alkene forms.
At 413 K, with excess alcohol, two molecules of alcohol lose one molecule of water between them and an ether forms.
\( \displaystyle \ce{C2H5OH} \xrightarrow[443\ \mathrm{K}]{\ce{H2SO4}} \ce{CH2=CH2 + H2O} \)
\( \displaystyle \ce{2C2H5OH} \xrightarrow[413\ \mathrm{K}]{\ce{H2SO4}} \ce{C2H5-O-C2H5 + H2O} \)
The reaction here is carried out at 443 K, so Y is ethene, H2C=CH2.
Why the other options are incorrect
Option (1) C2H5OCH3 — Incorrect. Methoxyethane is an unsymmetrical ether with a methyl group. Ethanol alone has no source of a CH3–O unit; this ether is made by the Williamson synthesis, for example from sodium ethoxide and methyl iodide.
Option (2) C2H5OC2H5 — Incorrect. Ethoxyethane (diethyl ether) does form from ethanol and H2SO4, but at the lower temperature of 413 K, with ethanol in excess.
Option (3) CH3OCH3 — Incorrect. Methoxymethane is the ether formed by the dehydration of methanol, not ethanol; it has no C–C bond, while ethanol keeps its C–C bond in every product.
NCERT (2026-27 edition):
By Dehydration of Alcohols
Note: The same/similar question has been asked in different years by NTA as per the details given below:
| 2026 | 2025 | 2024 | 2023 | 2022 |
|---|---|---|---|---|
| 06-06 S1 22-05 S2 | – | – | – | – |