Question

4. a solution that is 0.025M in HCOOH and 0.025M in NaCOOH

Problem 7
I want to make a solution that will have [HCOO 1 3[HCOOH). I start with 100ml of a 0.1M HCOOH solution. How many ml of a 1M KOH solution
should I add?

Answer 1

KOH added : 7.5 ml

Further explanation

Buffer solution of weak acid HCOOH and strong base KOH

Reaction

initial = 100 ml 0.1 M HCOOH = 10 ml mol HCOOH, and x mlmol of KOH

KOH + HCOOH ⇒ COOHK + H₂O

x 10

x x x x

- 10-x x x

[HCOO - ] = 3[HCOOH]

`\tt (x)/(x+100~ml)=3(10-x)/(x+100)\\\\x=3(10-x)\\\\x=30-3x\\\\4x=30\rightarrow x=7.5~ml`