Question

For the following reaction, identify whether the compound in bold is behaving as an acid or a base.

H₃PO₄ + H₂O ⇌ H₂PO₄- + H₃O+
1) H₃O+
2) acid
3) base
4) neither
5) both

Answer 1

In the reaction provided, H₃PO₄ donates a proton to water, hence it behaves as a Brønsted-Lowry acid.

Step-by-step explanation:

To answer the student's question about whether the compound in bold (H₃PO₄) is behaving as an acid or a base in the reaction H₃PO₄ + H₂O ⇌ H₂PO₄⁻ + H₃O⁺, we employ the Brønsted-Lowry theory of acids and bases. Per this theory, an acid is a substance that donates a proton (H+), and a base is a substance that accepts a proton. In the given reaction, H₃PO₄ donates a proton to water to form the hydronium ion (H₃O⁺) and the dihydrogen phosphate ion (H₂PO₄⁻), which means H₃PO₄ is acting as an acid.

In the chemical equation H₃PO₄ + H₂O ⇌ H₂PO₄- + H₃O+, the compound in bold, H₂PO₄-, is behaving as an acid.

It is acting as an acid because it is donating a proton (H⁺) to the water molecule, forming H₃O⁺ (hydronium ion) and H₂PO₄- (conjugate base).

Therefore, the answer to the question is 2) acid.