What is the proper way to mix water and acid?

• A. Add acid to water (A → W).
• B. Add water to acid (W → A).
• C. Pour acid and water together at the same time slowly.
• D. Mix with dry chemical before adding water.

Answer: (A)

When diluting acids, the heat released is large, so the safer approach is to add the acid to water rather than the other way around. Pouring the acid slowly into a larger amount of water lets the heat be absorbed and dispersed by the water as the dilution occurs, which minimizes the risk of the mixture boiling or splashing back. Adding water to concentrated acid concentrates the heat at the point of contact, which can cause the liquid to splash and burn. The idea of pouring both together at the same time is unpredictable and can still produce dangerous splashes. Mixing with a dry chemical before adding water isn’t a proper method for safely diluting acid and can introduce new hazards.