Question

113. Alcohol can act as an acid as well as a base. Justify the statement.

Answer 1

Part 1: Definition of acid and base:

• According to Arrhenius, an acid is any substance that gives hydrogen ion $\left({\mathrm{H}}^{+}\right)$ in an aqueous solution.
• According to Arrhenius, a base is any substance that gives hydroxide ion $\left({\mathrm{OH}}^{-}\right)$ in an aqueous solution.

Part 2: Alcohol act as an acid and base:

• Alcohol is amphoteric i.e. it can act as both acid and base.
• The polarity of the $\mathrm{O}-\mathrm{H}$ bond facilitates the removal of positively charged hydrogen ions thereby forming alkoxide ions. Thus, alcohol acts as an acid.
• $\underset{\mathrm{Alcohol}}{\mathrm{R}-\mathrm{O}-\mathrm{H}}\to \underset{\mathrm{Alkoxide}\mathrm{ion}}{{\mathrm{RO}}^{-}}+\underset{\mathrm{Hydrogen}\mathrm{ion}}{{\mathrm{H}}^{+}}$
• The polarity of the $\mathrm{R}-\mathrm{OH}$ bond due to more electronegativity of oxygen atom facilitates the removal of negatively charged hydroxide ion. Thus, alcohol acts as a base.
• $\underset{\mathrm{Alcohol}}{\mathrm{R}-\mathrm{OH}}\to \underset{\mathrm{Alkyl}\mathrm{ion}}{{\mathrm{R}}^{+}}+\underset{\mathrm{Hydroxide}\mathrm{ion}}{{\mathrm{OH}}^{-}}$