Which of the following describes what happens when sodium ethoxide is added to water?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Ethanol and sodium hydroxide are formed, because water is a stronger acid than ethanol.
Water gives a proton to the ethoxide ion, and ethanol and hydroxide ion are formed:
\( \displaystyle \ce{C2H5O^-Na+ + H2O -> C2H5OH + NaOH} \)
The reaction goes this way because water is a better proton donor (a stronger acid) than ethanol. So alcohols are weaker acids than water, and the ethoxide ion, a better proton acceptor than OH−, is a stronger base than the hydroxide ion.
Why the other options are incorrect
Option (1) No reaction takes place, because ethanol and water are acids of the same strength. — Incorrect. Ethanol and water are not equally acidic. Water is the stronger acid, so it does react with the ethoxide ion.
Option (2) Ethanol and sodium hydroxide are formed, because ethanol is a stronger acid than water. — Incorrect. The products are right, but the reason is reversed: ethanol is a weaker acid than water. If ethanol were the stronger acid, water could not give its proton to the ethoxide ion.
Option (3) Ethanol and sodium hydroxide are formed, because the ethoxide ion is a weaker base than the hydroxide ion. — Incorrect. The products are right, but the ethoxide ion is a stronger base than the hydroxide ion; sodium ethoxide is a stronger base than sodium hydroxide.
NCERT (2026-27 edition):
7.4.4 Chemical Reactions – “Alcohols are, however, weaker acids than water. This can be illustrated by the reaction of water with an alkoxide.”
\( \displaystyle \underset{\text{Base}}{\ce{R-O^-}} + \underset{\text{Acid}}{\ce{H-O-H}} \ce{->} \underset{\text{Conjugate acid}}{\ce{R-O-H}} + \underset{\text{Conjugate base}}{\ce{^-OH}} \)
“This reaction shows that water is a better proton donor (i.e., stronger acid) than alcohol. Also, in the above reaction, we note that an alkoxide ion is a better proton acceptor than hydroxide ion, which suggests that alkoxides are stronger bases (sodium ethoxide is a stronger base than sodium hydroxide).”