In the proper procedure for combining acid and water, which should be added to which?

The proper procedure for combining acid and water is that acid should be added to water. This approach is crucial for safety reasons. When an acid is mixed with water, the reaction is exothermic, meaning it releases heat. If water is added to acid instead, the heat generated can cause the mixture to bubble and spatter, potentially leading to hazardous situations, such as chemical burns or splashes of concentrated acid.

By adding acid to water, the acid is diluted gradually, allowing the heat to dissipate more evenly throughout the solution. This method helps to ensure that the water can absorb the heat generated without boiling violently, which can occur if a concentrated acid is introduced into a smaller volume of water too quickly. Therefore, following this established protocol is important for safe laboratory practices.