The buffer range of buffer solution is PKA 1, and the PKA of formic acid is 3.75, so the HCOOH/HCOONa acid-base pair meets the requirements.

PH=PKa-lg[HCOOH]/[HCOONa]

LG[HCOOH]/[HCOONa]= PKa-PH = 3.75-3.2 = 0.55

[HCOOH]/[HCOONa]=3.55/ 1

The required volume of formic acid solution is 0.5×0.2×3.55/4.55/0.2=0.39 liter.

The required volume of sodium formate solution is 0.5× 0.2×1/4.55/0.2 = 0.11liter.