[PaintYourFuture]

Having lots of trouble finishing a physchem prac report on measuring pH..
A quinhydrone electrode was used, coupled with the calomel electrode (reference electrode). Both were in a beaker of acetic acid, deionised water and quinhydrone to saturate the solution. Sodium hydroxide was added in 2mL portions and the emf was recorded after each addition.

One of the first questions is to plot  :delta:E/  :delta:V  Vs Vbar. It tells me that Vbar = (V_n+1 + V_n)/2.

What is 'n' referring to? Is it the number of moles of the NaOH in each of the volumes? I'm not really sure what this equation is getting at..

[Borek]

I would guess these are consecutive total volumes of added NaOH, or something close to that.

[fledarmus]

What Borek said - V_n is the volume after the nth addition of a 2 mL portion of sodium hydroxide. Depending on the context of the problem it might represent either the total volume of the solution at that point (which I suspect is true in this case) or just the total volume of NaOH added. Basically, you are just taking the average of the volume during the (n+1) addition and comparing it to the energy change per unit added volume.

[PaintYourFuture]

Righto. That makes things more do-able. Thanks guys!