Which chemical is used to neutralize waste containing caustic soda?

• A. Hydrochloric Acid
• B. Ammonia
• C. Buffer 10 solution
• D. Potassium hydroxide

Answer: (A)

Neutralizing a caustic base like sodium hydroxide requires an acid to donate protons and form water and a salt. When a strong acid such as hydrochloric acid is added to the waste, the H+ from the acid reacts with the OH− from the sodium hydroxide to produce water, while the sodium ion pairs with chloride to form sodium chloride. The overall reaction is NaOH + HCl → NaCl + H2O. This brings the pH toward neutral and makes the waste safer for handling and disposal.

Other options don’t fit the goal: ammonia is a base and would not neutralize the caustic waste; a buffering solution resists pH change rather than actively neutralizing; potassium hydroxide is also a base, so it would not neutralize more base. Hydrochloric acid is the appropriate neutralizing agent.