Arrange water, ethanol and phenol in increasing order of acidity and give reason for your answer.

Explanation

Increasing order of acidity is ethanol `lt` water `lt` phenol. The phenoxide ion obtained after the removal of a proton is stabilised by resonance whereas the ethoxide ion obtained after the removal of a proton is destabilised by +I.effect of `-C_(2)H_(5)` group. Therefore phenol is stronger acid than ethanol.

On the other hand ethanol is weaker acid than water because electron releasing `-C_(2)H_(5)` group in ethanol increases the electron density on oxygen and hence the polarity of 0-H bond in ethanol decreases. This results in the decreasing acidic strength. Hence acidic strength increases in the order given above.