Question

what is the PH of a buffer solution prepared using 0.010M HCOOH and 0.010M HCOONa? HCOOH = 1.7722 x 10-4

Answer 1

What's the pKa for HCOOH.

pKa = - log Ka = -log 1.7722E-4 = you calculate it. My calculator is not working.
Then pH = pKa + log [(base)/(acid)]
pH = pKa + log [(HCOONa)/(HCOOH)]
pH = pKa + log [0.01/0.01] = pKa + log 1 = pKa + 0 = pKa which will about 3.7 or so but you need to calculate pKa more exactly .