Which one of the following orders of acid strength is correct ?
- RCOOH > ROH > HOH > HC CH
- RCOOH > HOH > ROH > HC CH
- RCOOH > HOH > HC CH > ROH
- RCOOH > HC CH > HOH > ROH
Answer
(2) RCOOH > HOH > ROH > HC CH
Solution
Acid strength depends on the stability of the conjugate base.
RCOO- is stabilised by resonance (charge spread over two O atoms) RCOOH is the strongest acid.
The alkyl group (+I effect) increases the electron density on O in RO-, RO- is less stable than HO- HOH > ROH.
As per NCERT, alcohols are weaker acids than water, and water is a stronger acid than ethyne (HC C- carries the charge on the less electronegative sp carbon).
RCOOH > HOH > ROH > HC CH
Answer: (2)