How to Mix Acid and Water Safely

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, however, even if it did, it's less likely to cause injuries than if you make the mistake of adding water to acid. When you add water to acid, the water boils and the acid may splatter and splash!

Extra Caution With Strong Acids

This rule is particularly important if you are working with strong acids that react completely with water. Mixing sulfuric acid and water is particularly risky because any 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. Add the acid in small amounts of volume and stir thoroughly prior to adding more.

Just Remember: Add the Acid

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

Protective Gear and a Fume Hood

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

If Acid Splashes

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