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Question: One of the following is a Bronsted acid but not a Bronsted base A.\({H_2}S\) B.\({H_2}O\) C.\(...

One of the following is a Bronsted acid but not a Bronsted base
A.H2S{H_2}S
B.H2O{H_2}O
C.HCO3−HC{O_3}^ -
D.NH3N{H_3}

Explanation

Solution

In this question, we have to identify which is a Bronsted acid but not a base. A bronsted acid is an acid which releases H+{H^ + } ions and a bronsted base is a base that accepts H+{H^ + } ions. A conjugate base has one less hydrogen ion or proton than the acid we started with. A conjugate acid has one more hydrogen ion or proton than the base we started with.

Complete step by step answer:
Now we will discuss the given options one by one.
The first option is H2S{H_2}S (hydrogen sulphide).
If H2S{H_2}S (hydrogen sulphide) dissociates and it will release a proton. The one which releases proton (H+)({H^ + }) is a bronsted acid but if H2S{H_2}S (hydrogen sulphide) accepts a proton; it will not make many compounds. Therefore, H2S{H_2}S (hydrogen sulphide) acts as a bronsted acid but not a bronsted base.
H2S⇌HS−+H+{H_2}S \rightleftharpoons H{S^ - } + {H^ + }
The second option is H2O{H_2}O (water). Water dissociates and releases a proton (H+)({H^ + }) to give H+{H^ + } and OH−O{H^ - } acts as a bronsted acid. If water accepts a proton it will give H3O+{H_3}{O^ + } and acts as a bronsted base.
H2O+H+→H3O+{H_2}O + {H^ + } \to {H_3}{O^ + }
H2O⇌H++OH−{H_2}O \rightleftharpoons {H^ + } + O{H^ - }
The third option is HCO3−HC{O_3}^ - (bicarbonate ion). Bicarbonate ion will also dissociate and releases a proton (H+)({H^ + }) to give carbonate ion (CO32−)(C{O_3}^{2 - }) and acts as a bronsted acid. If it accepts a proton it will give carbonic acid (H2CO3)({H_2}C{O_3}) and acts as a bronsted base.
HCO32−⇌CO32−HC{O_3}^{2 - } \rightleftharpoons C{O_3}^{2 - }
HCO32−+H+→H2CO3HC{O_3}^{2 - } + {H^ + } \to {H_2}C{O_3}
The fourth option is NH3N{H_3} (ammonia). Ammonia also dissociates and releases proton (H+)({H^ + }) to give NH2−N{H_2}^ - and acts as a bronsted acid. Ammonia also accepts a proton to give ammonium cation (NH4+)(N{H_4}^ + ) and acts as a bronsted base.
NH3+H+→NH4+N{H_3} + {H^ + } \to N{H_4}^ +
NH3⇌NH2−+H+N{H_3} \rightleftharpoons N{H_2}^ - + {H^ + }
After discussing it we can conclude that H2S{H_2}S (hydrogen sulphide) acts as a bronsted acid but not a bronsted base.
Hence, the correct option is (A).

Note:
We take an example for the explanation of the Bronsted-Lowry acid-base concept.
HCl+NH3⇌NH4+Cl−HCl + N{H_3} \rightleftharpoons N{H_4} + C{l^ - }
Hydrochloric acid is a bronsted- lowry acid because it donates a hydrogen ion or proton.
Ammonia is a bronsted- lowry base because it accepts the hydrogen ion or proton.
The Bronsted-Lowry theory comes with the concept of conjugate acid-base pair.