Question #e1635

You can think of a `96:4` glacial acetic acid and acetonitrile solution as being equivalent to a `96%"v/v"` glacial acetic acid/acetonitrile solution.

In simple terms, you need the target solution to be `96` parts by volume glacial acetic acid and `4` parts by volume acetonitrile.

This is equivalent to saying that out of `100` parts of solution, `96` will be glacial acetic acid and `4` acetonitrile.

So, your target solution has a volume of `"500 mL"`. In order to keep the above proportions, you would need it to contain

`500 color(red)(cancel(color(black)("mL solution"))) * ("96 mL CH"_3"COOH")/(100color(red)(cancel(color(black)("mL solution")))) = color(green)("480 mL")` `"CH"_3"COOH"`

and

`500 color(red)(cancel(color(black)("mL solution"))) * ("4 mL CH"_3"CN")/(100color(red)(cancel(color(black)("mL solution")))) = color(green)("20 mL")` `"CH"_3"CN"`

And there you have it. If you mix `"480 mL"` of glacial acetic acid and `"20 mL"` of acetonitrile, you'll get `"500 mL"` of a `96:4` glacial acetic acid/acetonitrile solution.