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.