Final answer:
In the given reaction, water acts as both a Brønsted-Lowry base and a Brønsted-Lowry acid. It can accept a proton when reacting with a stronger acid, and it can donate a proton when reacting with a stronger base.
Step-by-step explanation:
In the reaction HSO₄ + H₂O → H₃O + SO₄-2, water acts as both a Brønsted-Lowry base and a Brønsted-Lowry acid. It can act as a proton acceptor (base) when it reacts with a stronger acid, and it can also act as a proton donor (acid) when it reacts with a stronger base.
The Brønsted-Lowry theory is one of the three major classifications of acids and bases. It defines an acid as a substance that donates a proton and a base as a substance that accepts a proton. In this reaction, water can accept a proton (base) from the hydrogen sulfate ion or donate a proton (acid) to the sulfate ion.
In the reaction HSO₄⁻ + H₂O → H₃O⁺ + SO₄⁻², according to the Brönsted-Lowry acid-base theory, the H₂O molecules act as Brönsted-Lowry bases because they accept a proton from the hydrogen sulfate ion (HSO₄⁻). Water can also act as a Brönsted-Lowry acid when it donates a proton to another substance, but in this reaction, it is gaining a proton. Thus, the answer is that H₂O molecules act as a Brönsted-Lowry base in this specific reaction.