Which chemical may be used to neutralize waste containing phosphoric acid?

• A. Hydrochloric Acid
• B. Sodium Hydroxide
• C. Distilled Water
• D. Acetone

Answer: (B)

Neutralization reactions between acids and bases are what this item is probing. Phosphoric acid can donate protons, so to neutralize it you need a base that supplies hydroxide ions. Sodium hydroxide fits that role perfectly because it provides OH- that combine with the H+ from the acid to form water, leaving a phosphate salt. The typical neutralization product is Na3PO4 plus water, shown by the balanced equation H3PO4 + 3 NaOH → Na3PO4 + 3 H2O. That's why sodium hydroxide is the best choice: it reliably neutralizes the acid and yields a safe salt and water. In contrast, hydrochloric acid would add more acid, distilled water would only dilute, and acetone is a solvent and does not neutralize the acid.