Consider the following statements about the acidic character of alcohols.
(A) Alcohols react with active metals such as sodium, potassium and aluminium to yield the corresponding alkoxides and hydrogen.
(B) Alcohols are stronger acids than water, as shown by the reaction of water with an alkoxide.
(C) Sodium ethoxide is a stronger base than sodium hydroxide.
(D) In an alcohol, an electron-releasing group such as –CH3 or –C2H5 increases the polarity of the O–H bond.
Which of the statements given above are incorrect? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (B) and (D) only
Alcohols are Brönsted acids: the polar O–H bond lets them give a proton to a stronger base. Their acid strength is low, lower even than that of water.
(A) Alcohols react with active metals such as sodium, potassium and aluminium to yield the corresponding alkoxides and hydrogen. — Correct statement. The metal replaces the hydrogen of the O–H group:
\( \displaystyle \ce{2R-OH + 2Na -> 2R-O^-Na+ + H2} \)
(B) Alcohols are stronger acids than water, as shown by the reaction of water with an alkoxide. — Incorrect statement. Alcohols are weaker acids than water. Water gives its proton to the alkoxide ion and the alcohol is set free, so water is the better proton donor:
\( \displaystyle \ce{R-O^- + H-OH -> R-OH + OH^-} \)
(C) Sodium ethoxide is a stronger base than sodium hydroxide. — Correct statement. In the same reaction the alkoxide ion takes a proton from water, so it is a better proton acceptor than the hydroxide ion.
(D) In an alcohol, an electron-releasing group such as –CH3 or –C2H5 increases the polarity of the O–H bond. — Incorrect statement. The group pushes electrons towards oxygen, which decreases the polarity of the O–H bond and so lowers the acid strength.
NCERT (2026-27 edition):
7.4.4 Chemical Reactions – “(i) Reaction with metals: Alcohols and phenols react with active metals such as sodium, potassium and aluminium to yield corresponding alkoxides/phenoxides and hydrogen.”
“(ii) Acidity of alcohols: The acidic character of alcohols is due to the polar nature of O–H bond. An electron-releasing group (–CH3, –C2H5) increases electron density on oxygen tending to decrease the polarity of O-H bond. This decreases the acid strength.”
“Alcohols are, however, weaker acids than water. This can be illustrated by the reaction of water with an alkoxide.” … “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).”