Question

How do you prepare a 1.0 L buffer with pH 5, using Oxalic acid and its sodium salt(s)?

Answer 1

To prepare a 1.0 L buffer with pH 5, using Oxalic acid and its mono sodium salt use following steps:
so as we know

pH = pKa + log [salt]/[acid]

Here pH = 5.0 pKa = 4.19

5= 4.19+ log [salt] / [acid]

0.81 = log [salt]/[acid]

taking anitlog...


[salt]/[acid] = 6.46

no. of moles of salt / no. of moles of acid = 6.46

and the molarity = no. of moles of solute / volume of solutionin litres

so no. of moles of solute = molarity X volume of solution in litres

as the buffer solution is of 1000 ml or 1.0 L

let acid = x L ...then

salt = 1.0-x L

no. of moles of acid = 1.0*X
no. of moles of salt = 1.0* (1.0-X)

putting in above relation

no. of moles of salt / no. of moles of acid = 6.46
1.0* (1.0-X) / 1.0*X = 6.46


x = 0.134 L

x = volume of acid used 0.134 L or 134 ml
1.0-x = volume of salt used = 0.866 L or 866 ml