berapa gram kristal NaOH yang harus dimasukkan ke dalam 100 mL larutan HCOOH 0,1 M (ka = 2 x 10-⁴) untuk membuat laruta. penyangga dengan ph = 4-log4

mmol HCOOH = 0,1 x 100 = 10mmol
pH = 4-log 4 , [H+] = 4 x 10^-4
Ka = 2 x 10^-4
Mr NaOH = 40

NaOH + HCOOH -> HCOONa + H2O
x 10mmol - -
x x x x
- 10mmol - x x x

[H+] = Ka . mmol asam / mmol garam
4 x 10^-4= 2 x 10^-4 . 10- x mmol / x mmol
4 x 10^-4 / 2 x 10^-4 = 10- x mmol / x mmol
2 = 10 - x mmol / x mmol
2x =10mmol - x mmol
2x + x mmol = 10 mmol
3x mmol = 10 mmol
x = 10/3 mmol
= 3.3 mmol

3,3 mmol = mg NaOH / Mr NaOH (
3,3 x 40 = mg NaOH
132 = mg => 132 : 1000 = 0,132 gr