JEE MAIN - Chemistry (2022 - 25th June Evening Shift - No. 6)
Given below are two statements one is labelled as Assertion A and the other is labelled as Reason R :
Assertion A : The amphoteric nature of water is explained by using Lewis acid/base concept.
Reason R : Water acts as an acid with NH3 and as a base with H2S.
In the light of the above statements choose the correct answer from the options given below :
Both A and R are true and R is the correct explanation of A.
Both A and R are true but R is NOT the correct explanation of A.
A is true but R is false.
A is false but R is true.
Explanation
The amphoteric nature of water is explained by
using Bronsted-Lowry acid base concept
$$\underset{\text { (acid) }}{\mathrm{H}_{2} \mathrm{O}}+\mathrm{NH}_{3} \rightleftharpoons \mathrm{OH}^{-}+\mathrm{NH}_{4}^{+}$$
$$\underset{\text { (base) }}{\mathrm{H}_{2} \mathrm{O}}+\mathrm{H}_{2} \mathrm{~S} \rightleftharpoons \mathrm{H}_{3} \mathrm{O}^{+}+\mathrm{HS}^{-}$$
Hence, A is false but R is true
$$\underset{\text { (acid) }}{\mathrm{H}_{2} \mathrm{O}}+\mathrm{NH}_{3} \rightleftharpoons \mathrm{OH}^{-}+\mathrm{NH}_{4}^{+}$$
$$\underset{\text { (base) }}{\mathrm{H}_{2} \mathrm{O}}+\mathrm{H}_{2} \mathrm{~S} \rightleftharpoons \mathrm{H}_{3} \mathrm{O}^{+}+\mathrm{HS}^{-}$$
Hence, A is false but R is true
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