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Do You Add Sulfuric Acid to Water or Water to Sulfuric Acid?

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If you don't mix concentrated sulfuric acid and water correctly you could end up with a burn.

If you don't mix concentrated sulfuric acid (pictured) and water correctly you could end up with a serious acid burn.

Ben Mills

Question: Do You Add Sulfuric Acid to Water or Water to Sulfuric Acid?

When you mix concentrated sulfuric acid and water, you pour the acid into a larger volume of water. Mixing the chemicals the other way can present a lab safety hazard.

Answer: Whether you add acid to the water or water to the acid is one of those things I know it's important to remember, but always have to puzzle out. Sulfuric acid (H2SO4) reacts very vigorously with water, in a highly exothermic reaction. If you add water to concentrated sulfuric acid, it can boil and spit and you may get a nasty acid burn. If you spill some sulfuric acid on your skin, you want to wash it off with copious amounts of running cold water as soon as possible. Water is less dense than sulfuric acid, so if you pour water on the acid, the reaction occurs on top of the liquid. If you add the acid to the water, it sinks and any wild and crazy reactions have to get through the water or beaker to get to you. How do you remember this? Here are some mnemonics:

  • AA - Add Acid
  • Acid to Water, like A&W Root Beer
  • Always do things as you oughta, add the acid to the water. (um... no... those words don't rhyme in most places.)
  • Drop acid, not water. (Don't do that either, ok?)
  • If you think your life's too placid, add the water to the acid.

Personally, I don't find any of those mnemonics easy to remember. I get it right because I figure if I get it wrong, I'd rather have a whole container of water splash on me than a whole container of sulfuric acid, so I take my chances with the small volume of acid and the large volume of water.

What About Mixing Other Acids and Water?

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