The Cardinal Rule of Acid Dilution
The most important rule when diluting a concentrated acid is to always add the acid slowly to the water, never the other way around. This is often remembered by the mnemonic "Do as you oughta, add acid to water." Following this rule is crucial for preventing dangerous chemical splashes and ensuring safety in the laboratory.
Section 2: The Science Behind the Rule
When strong acids like sulfuric acid are mixed with water, a significant amount of heat is released in a process called an exothermic reaction. The solvation (dissolving) of acid ions is highly energetic. If you add water to a large amount of acid, the small volume of water heats up so rapidly it can boil instantly, splashing the concentrated acid out of the container.
Section 3: A Practical Example
Imagine adding a small amount of water to a beaker of concentrated sulfuric acid. The first few drops of water react so violently they can flash into steam. This steam expands rapidly, creating an explosion-like effect that can splash the highly corrosive acid. Since acid is denser than water, the water would float on top, causing this dangerous reaction to occur right at the surface.
Section 4: Why Adding Acid to Water is Safer
When you add acid slowly to a larger volume of water, the heat generated is absorbed by the entire body of water. Water has a high specific heat capacity, meaning it can absorb a lot of heat without a large increase in temperature. This prevents the solution from boiling violently. The denser acid also sinks and mixes more evenly, distributing the heat safely.