Chemistry Question #806

Eric Leclair, a 29 year old male from Ottawa asks on June 1, 2002,

In the past, I have used Vinegar to kill unwanted weeds along walkways, around the patio, etc... But if one wants to use acetic acid as a truly effective organic weed killer, it is recommended to use a spray dispenser using a solution with 20 to 25% acetic acid. I believe acetic acid has a boiling point of 118 degrees C. To increase the concentration, could I slowly boil a volume of vinegar? Would this work? Could you supply me with helpful hints/techniques to effectively accomplish this task?

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The answer

Reg Mitchell answered on June 10, 2002

Boiling vinegar will not concentrate it, since the acetic acid will boil away as well as the water due to it forming an azeotrope with the water. You will get a very little bit of concentration, perhaps. To effectively concentrate it, you have to do fractional distillation. You can find out how to do this on the web by looking up "fractional distillation" in google. By far the easier thing to do is just buy glacial acetic acid from a chemical supply house. Be careful with it, however.

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