When mixing water and acid, which should be added first?

When mixing water and acid, the correct procedure is to add acid to water. This is crucial because adding water to acid can cause a violent reaction that may lead to splattering and potential hazards. When acid is poured into water, the water acts as a buffer and absorbs the heat generated by the reaction, reducing the risk of splashing and ensuring a safer mixing process.

The reaction between water and acid is exothermic, which means it releases heat. If water is added to concentrated acid, the intense heat produced can cause the water to rapidly vaporize. This can create a dangerous situation as the steam and acid mixture can splash back, potentially causing burns or injuries.

The other options, such as mixing equal amounts simultaneously or adding water to acid, are not safe practices. These methods can lead to uncontrolled reactions and pose significant safety risks. By following the correct procedure of adding acid to water, individuals ensure a safer and more controlled reaction.