Question

Assertion :According to Bronsted concept, $H_{2}O$ is an amphoteric substance. Reason: $H_{2}O$ molecule can accept as well as donate a proton.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Assertion is incorrect but Reason is correct

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

In the Bronsted Lowry theory, an acid donates a proton and the base accepts it. The ion or molecule remaining after the acid has lost a proton is known as that acid's conjugate base, and the species created when the base accepts the proton is known as the conjugate acid.

This is expressed in the following reaction:

acid + base$\to$conjugate base + conjugate acid.

Water is amphoteric and can act as an acid or as a base. In the reaction between acetic acid, $C{H}_{3}C{O}_{2}H$, and water, $H_{2}O$, water acts as a base.

$C{H}_{3}COOH+H_{2}O\to C{H}_{3}CO{O}^{-}+H_3{O}^{+}$

The acetate ion, $C{H}_{3}C{O}_2^{-}$, is the conjugate base of acetic acid and the hydronium ion, $H_3{O}^{+}$, is the conjugate acid of the base, water.

Water can also act as an acid, for instance when it reacts with ammonia. The equation given for this reaction is:

$H_{2}O+N{H}_3\to O{H}^{-}+N{H}_4^{+}$

The hydroxide ion is the conjugate base of water acting as an acid and the ammonium ion is the conjugate acid of the base, ammonia.