[Sam 3-ol]

     OK so I have been trying to figure this out and it is really frustrating me. I need to figure out how much 5% ethanoic acid (solution in water) to add to 1 liter of water to bring the ph down from 7 to 6.5.
     
      I can't seem to get any grasp on this. I asked my teacher to explain this to me but he confused me even more. I am very good at math so I don't even know why I can't get this. A simple equation would help me a lot example (x-y=z).

     So what is the answer to this question and more importantly how do I find it. (something that I could relate to other acids and bases would be helpful too)

[Fluoroantimonicacid]

Take the solution amount x and set an equillibrium up with it. Don't forget to consider the initial conc. of H⁺ 10^-7 M.

[Borek]

Compare http://www.chembuddy.com/?left=pH-calculation&right=pH-acid-base-solution