Question

A 0.10 M solution of formic acid (HCOOH) is prepared in various solvents: (a) pure water, (b) 0.10 M NaHCOO solution, (c) 0.10 M Ca(HCOO)2 solution, and (d) 0.10 M NaCl. Compute the pH of each solution. The Ka of formic acid is 1.78*10^-4.

Answer 1

a)$pH=1/2(pK_a-log(c_0))=2.38$

b)$pH=pK_a+log\left(\frac{c(NaHCOO)}{c(HCOOH)}\right)=pK_a=3.75$

c) $pH=pK_a+log\left(\frac{2c(Ca(HCOO)_2)}{c(HCOOH)}\right)=pK_a+log(2)=4.05$

d)$pH=2.38$