Question

When dihydrogen phosphate ion reacts with water, water acts as a Brønsted-Lowry base. Choose the reaction that describes this.

A. HPO_4^2−(aq) + H_2O(l) ⇌ H_3O^+(aq) + PO_4^3−(aq)
B. H_2PO_4^−(aq) + H_2O(l) ⇌ OH−(aq) + H_3PO_4(aq)
C. H_2PO_4^−(aq) + H_2O(l) ⇌ H_3O^+(aq) + HPO_4^2−(aq)
D. H_2PO_4^−(aq) + H_3O^+(aq) ⇌ H_2O(l) + H_3PO_4(aq)

Answer 1

The correct reaction that shows water acting as a Brønsted-Lowry base is option B, where dihydrogen phosphate ion donates a proton to water, forming OH^- and H3PO4.

Step-by-step explanation:

When the dihydrogen phosphate ion (HPO4^2−) reacts with water (H2O), the water molecule functions as a Brønsted-Lowry base by accepting a proton. The correct reaction that describes this process is the following:

• B. H2PO4^-…(aq) + H2O(l) ⇌ OH^-…(aq) + H3PO4(aq)

In this reaction, the dihydrogen phosphate ion (H2PO4^-) acts as a Brønsted-Lowry acid by donating a proton to water, which then generates a hydroxide ion (OH^-) and phosphoric acid (H3PO4). This shows the amphoteric nature of the dihydrogen phosphate ion, able to act both as an acid and a base.