In: Chemistry
HClO is a weak acid (Ka = 4.0 × 10–8) and so the salt NaClO acts as a weak base. What is the pH of a solution that is 0.026 M in NaClO at 25 °C?
Given Ka = 4.0x10-8
Kb of the base is = Kw / Ka
= (1.0x10-14) / (4.0x10-8)
= 2.5x10-7
OCl- + H2O HOCl + OH-
Kb = ([HOCl][OH- ]) / [OCl-]
2.5x10-7 = [OH- ]2 / [OCl-] Since [HOCl]=[OH- ]
[OH- ] = (2.5x10-7 x[OCl-])
= (2.5x10-7 x0.026)
= 8.06x10-5 M
pOH = - log[OH- ]
= - log(8.06x10-5)
= 4.1
We know that pH + pOH = 14
So pH = 14 - pOH
= 14 - 4.1
= 9.9
Therefore the pH of the solution is 9.9