How to Mix Acid and Water Safely

A dropper of liquid held over a beaker.
Ann Cutting / Getty Images

When you mix acid with water, it's extremely important to add the acid to the water rather than the other way around.

This is because acid and water react in a vigorous exothermic reaction, releasing heat, sometimes boiling the liquid. If you add acid to water, the water is unlikely to splash up, but even if it did, it's less likely to hurt you than if you add water to acid. When water is added to acid, the water boils and the acid may splatter and splash!

This rule is particularly important if you are working with strong acids, which react completely with water. Mixing sulfuric acid and water is particularly risky because the splashed acid is corrosive enough to immediately burn skin and clothing. When mixing sulfuric acid or another strong acid, start with a volume of water large enough to absorb the heat of the reaction and add stir in the acid a small volume at a time.

An easy way to remember the rule is "Add the Acid".

Mix Acid and Water Safely

Because of the risk of splashes and release of dangerous fumes, acids and water should be mixed inside a fume hood. Protective goggles, gloves, and a lab coat should be worn.

In most cases, an acid splash should be treated by rinsing the affected area with running water. Acid splashes onto the lab bench or other surfaces may be neutralized by adding a weak base solution (e.g., baking soda in water). Although a strong base neutralizes an acid more quickly than a weak base, a strong base should never be used because the reaction between the strong base and the acid releases a lot of heat.