I have to be missing something here, something obvious, but I just don't understand what's going on here.
200Cm3 of 3.2 mol dm-3 HCOOH,
800Cm3 of 0.5 mol dm-3 NaOH
Buffer volume = 1dm3
Ka is 1.4*10-4
The conc. of H+ is Ka*HA/A isn't it?
But the values given already are concentrations and it can't be to do with "total volume" because it's 1.
The markscheme values in the calculation are 0.4 for NaOH, (isn't that the no. of moles??? Conc*volume?),
and 0.24 for HCOOH... where on Earth is that value even coming from?