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Why is sulfuric acid added to water rather than water added to concentrated sulfuric acid?
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The structure of phosphorous acid, H3PO3.
Sulfuric acid should always be added to water, rather than adding water to concentrated sulfuric acid, to ensure safety in the laboratory.
The reaction between anhydrous sulfuric acid and water is highly exothermic, meaning it releases a significant amount of heat. If water is added to concentrated sulfuric acid, the intense heat generated can cause the water to boil instantly, leading to explosive spattering of the corrosive acid.1
To minimize the risk of injury, you should always add the acid to the water slowly while stirring. This method allows the heat produced by the reaction to be distributed throughout the larger volume of water, preventing localized overheating and dangerous splashing.1