Question

Arrange : Water, ethanol and phenol in increasing order of acidity and give reasons for your answer.

Answer 1

Hint : When a hydrogen atom in an aliphatic or aromatic hydrocarbon is replaced by a –OH group, alcohols and phenols are formed. Compound groups have a wide range of uses in business and everyday life.

Complete Step By Step Answer:
Since phenol has a propensity to lose H+ ion and form phenoxide ions, it is more acidic than water. As water loses ${H^ + }$ ion, it forms hydroxide, which is not stabilised by resonance. Water with a pH greater than ethanol is more acidic than ethanol.
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 the effect of — ${C_2}{H_5}$ group. Therefore phenol is a stronger acid than ethanol. However, ethanol is a weaker acid than water since the electron releasing — ${C_2}{H_5}$ group in ethanol increases the electron density on oxygen, resulting in a decrease in the polarity of $O--H$ the bond in ethanol, resulting in a decrease in acidic strength. As a result, acidic intensity rises in the order mentioned above.
Also we can say that, this is due to the fact that the phenoxide ion formed after the removal of is ${H^ + }$ resonance stabilised, while the ethoxide ion formed after the removal of ${H^ + }$ is destabilised due to the +1 effect of the ethyl community. As a result, phenol is a more powerful acid than ethanol.
Increasing order of acidity is: ethanol < water < phenol.

Note :
The conjugate base is weaker while the acid is heavier. As a consequence, any factor that raises acidity by stabilising the conjugate base. The donation of a proton ${H^ + }$ from an acid to a base is known as an acid-base reaction. The acid is the species that loses ${H^ + }$ .