Question

The hydrogen sulfate or bisulfate ion, \[HSO_4^ - \] , can act as either an acid or a base in water solution. in which of the following equations does \[HSO_4^ - \] act as an acid?
A.\[HSO_4^ - + {H_2}O \to {H_2}S{O_4} + O{H^ - }\]
B.\[HSO_4^ - + {H_3}{O^ + } \to S{O_3} + 2{H_2}O\]
C.\[HSO_4^ - + O{H^ - } \to {H_2}S{O_4} + {O^{2 - }}\]
D.\[HSO_4^ - + {H_2}O \to SO_4^{2 - } + {H_3}{O^ + }\]
E.None of these

Answer 1

Hint: The Bronsted-Lowry acid is a molecule or compound which donates a proton to the other compound. A conjugate base is the one that can accept a proton and acid reforms. The Bronsted-Lowry base is the one which accepts a proton ion from other compounds. A conjugate acid is the one that can donate a proton and base reforms.

Complete step-by-step answer:
Hydrogen sulfate is also known as bisulfate which is an anion and it has a formula \[HSO_4^ - \] . Hydrogen sulphate is formed using the chemical radical sulphate \[(HS{O_4})\] . When it is exposed to water, they react with each other to form sulfuric acid. With the sulfate radial, we can tell that they are generally acidic in nature. We also use them as a weaker alternative to sulfuric acid. It reacts with sodium to form sodium bisulfate, a pure substance.
One of its chemical properties is, it is highly reactive with distilled water and forms sulfate and hydronium ions. The chemical equation for this chemical reaction is
 \[HSO_4^ - + {H_2}O \to SO_4^{2 - } + {H_3}{O^ + }\]
We get some information from this reaction which is that in this reaction, \[HSO_4^ - \] act as an acid as it gives away a proton. As per Bronsted-Lowry, acid is the one which gives away a proton and base is the one which gives away a hydroxide ion.
Let us now look at the other options given to us. In option A, \[HSO_4^ - \] acts as base as it accepts a proton from water molecules. In option B, it again acts as a base because it gives away hydroxide ion and forms sulfur trioxide. In option C, it acts as a base because it again accepts a proton from hydroxide ions. Only in option D, it acts as an acid by giving away a proton.
Hence the correct option is (D).

Note: As per Bronsted-Lowry, an acid-base reaction basically occurs when there is a transfer of one proton from one ion or molecule to another ion or molecule. In the above correct option, water acts as a base since it reacts with bisulfite ion, a better proton donor. This is due to the amphoteric nature of water i.e. it can act both as a base and acid.