Question

formic acid is a weak acid Ka= 1.9 x 10^-4 . Calculate the ph of a .50M solution of formic acid. what is the degree of ionization?

Answer 1

HCOOH, formic acid is a weakest acid that does not dissolve completely in the aqueous solution. That is there is an equilibrium is formed between unionised and ionised forms of acid.

We can use ICE table to find the concentration of hydronium ion and conjugate base.

	(aq)	(aq)	(aq)
Initial (I)	0.50 M	0	0
Change (C)	(-x)	(+x)	(+x)
Equilibrium (E)	(0.50-x)M	x	x

  ​​​​​​

0.50-x is very small value. Thus we can approximate it to 0. 50M,

That is concentration of H3O+,

  

We can calculate pH as,

  pH = 2.011

Degree of ionization is the ratio of concentration of H+ and the acid HA.

Degree of ionization =

=  

=

= 0.0189