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Question: The hydrogen sulfate or bisulfate ion, \(HS{O_4}^ - \), can act as either an acid or a base in water...

The hydrogen sulfate or bisulfate ion, HSO4−HS{O_4}^ - , can act as either an acid or a base in water solution. In which of the following equations does HSO4−HS{O_4}^ - act as an acid?
(A) HSO4−  +   H2O   →  H2SO4  +  OH−HS{O_4}^ - \,\, + \,\,\,{H_2}O\,\,\, \to \,\,{H_2}S{O_4}\,\, + \,\,O{H^ - }
(B) HSO4−  +   H3O+   →  SO3  +  2H2OHS{O_4}^ - \,\, + \,\,\,{H_3}{O^ + }\,\,\, \to \,\,S{O_3}\,\, + \,\,2{H_2}O
(C) HSO4−  +   OH−   →  H2SO4  +  O2−HS{O_4}^ - \,\, + \,\,\,O{H^ - }\,\,\, \to \,\,{H_2}S{O_4}\,\, + \,\,{O^2}^ -
(D) HSO4−  +   H2O   →  SO42−  +  H3O+HS{O_4}^ - \,\, + \,\,\,{H_2}O\,\,\, \to \,\,S{O_4}^{2 - }\,\, + \,\,{H_3}{O^ + }

Explanation

Solution

In this question, we are discussing the Conjugate acid and conjugate base. So, here we have to determine whether the hydrogen sulfate or bisulfate ion is conjugate acid or conjugate base.

Complete step by step answer:
Conjugate Acid-Base pair: Those acids and bases which exist as pairs or are conjugate of each other are termed as conjugate acid-base pairs. The term conjugate comes from the Latin stems meaning "joined together" and refers to things that are joined, particularly in pairs, such as Bronsted acids and bases.
Every time a Bronsted acid acts as a hydronium ion donor, it forms a conjugate base. Imagine a generic acid, HAHA. When this acid donates an H+{H^ + } ion to water, one product of the reaction is the A−{A^ - } ion, which is a hydrogen-ion acceptor, or Bronsted base.
HA+H2O⇄H3O++A−HA + {H_2}O \rightleftarrows {H_3}{O^ + } + {A^ - }
Conversely, every time a base gains an H+{H^ + } ion, the product is a Bronsted acid, HAHA.
A−+H2O⇄HA+OH−{A^ - } + {H_2}O \rightleftarrows HA + O{H^ - }
Acids and bases in the Bronsted model therefore exist as conjugate pairs whose formulas are related by the gain or loss of a hydrogen ion.
According to the question,
(A) HSO4−HS{O_4}^ - Acts as base as it accepts H+{H^ + } ion
(B) HSO4−HS{O_4}^ - Acts as base as it gives away OH−O{H^ - } ion
(C) HSO4−HS{O_4}^ - Acts as base as it accepts H+{H^ + } ion
HSO4−HS{O_4}^ - Acts as acid as it gives away H+{H^ + } ion

So, Option (D) is correct.

Note: How to identify the conjugate acid- base pair
-A conjugate acid contains one more hydrogen atom and one more +ve + ve charge than the base that formed it.
-A conjugate base contains one less hydrogen atom and one more −ve - ve charge than the acid that formed it.