What is the proper rule for mixing acids and water?

The correct approach for mixing acids and water is to add acid to water slowly while stirring. This method is crucial because when an acid is added to water, it can release a significant amount of heat through an exothermic reaction. If water is poured into a concentrated acid, especially quickly, it can cause a violent reaction that may lead to splattering and potentially dangerous outcomes.

By adding acid to water, the heat generated is absorbed by the larger volume of water, which helps to prevent any sudden or violent reactions. Stirring the mixture while adding the acid allows for even distribution of heat and dilution, further ensuring safety.

This practice aligns with safety protocols in laboratory settings and is a fundamental principle in chemical handling to mitigate risks associated with acid spills or chemical reactions.