Question

What is the pH of a 0.25 M solution of KCOOH?

Answer 1

Given that [KCOOH] , C = 0.25 M

We know that Ka of Formic acid HCOOH = 1.8 x 10^-4

Since KCOOH is base, we need Kb.

we know that Ka. Kb = Kw

Kb = Kw/ Ka = 10^-14/ 1.8 x 10^-4 = 0.55 x 10^-10

we know that [OH-] = (Kb. C) ^1/2

   ⁼ (0.55 x 10^{-10 .} 0.25) ^1/2

   = 0.37 X 10^-5

^{pOH = - log [OH-]}

   = - log [0.37 X 10^-5]

^{= 5- log 0.37}

   ^{= 5-(-0.43)}

^{= 5.43}

^{Hence, pOH =5.43}

^{Then, pH = 14 - pOH}

   ^{= 14-5.43}

   ^{= 8.57}

pH = 8.57

Therefore, pH of 0.25 M solution of KCOOH = 8.57