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chemistry a level help

A buffer solution is to be made using 1.00 mol dm–3 ethanoic acid, CH3CO2H, and
1.00 mol dm–3 sodium ethanoate, CH3CO2Na.
Calculate to the nearest 1 cm3 the volumes of each solution that would be required to
make 100 cm3 of a buffer solution with pH 5.50.
Clearly show all steps in your working.

Ka (CH3CO2H) = 1.79 × 10–5 mol dm–3

Reply 1

GabiAbi84

What have you done so far?

Reply 2

zohhaa

Original post by GabiAbi84

What have you done so far?

Ok so I used the equation pH=pka+log([base]/[acid])
I got [base]/[acid]=5.66, but I have no idea how to proceed further, since I don't know the number of moles of the ethanoic acid or of sodium ethanoate, however in the answer key they have simply put it like this
B+A=100, B=100-A (B=base, A=acid)
(100-A)/A=5.66 and they got the volume of acid as 15cm^3 and of base 85cm^3.

I'm confused why do they directly take the volumes isn't /[A]=5.66 the ratio of the concentrations of the respective species so shouldn't we be doing (number of moles of base/V) divided by (number of moles of acid/100-V), but the problem is they haven't given us the initial volumes of the solutions, they've only given the conc, so how do we calculate moles??
Can someone please explain?