Question

Indicate the ionic species of phosphoric acid that predominates at pH 4, 8, and 11. The answer is: pH 4, H2PO4- pH 8, HPO4 2- pH 11, HPO4 2- Need an explanation and calculation why is that

Answer 1

Phosphoric acid (H3PO4) exists in different ionic species depending on the pH value. At pH 4, H2PO4- predominates, at pH 8 and 11, HPO4 2- predominates.

Step-by-step explanation:

Phosphoric acid (H3PO4) is a polyprotic acid, meaning it has multiple dissociation steps. At different pH values, different ionic species of phosphoric acid predominate:

• At pH 4, the predominant ionic species is H2PO4-.
• At pH 8, the predominant ionic species is HPO42-.
• At pH 11, the predominant ionic species is also HPO42-.

The degree of ionization in each successive step decreases significantly, resulting in different ionic species dominating at different pH values.