Since this isia weak acid- base titration so,
CH3COOH having 55.0ml(. 055 l) and .3M
for mole, . 055* . 3=0.0165 mole
So for NaOH 0.1650 l mixed with 0.1M soln to have 0.0165 mole of NaOH
NaOH + CH3CHOOH = NaCH3COO + H2O
Initial 0.0165 0.0165 0
Equilibrium 0 0 0.0165
Now Molarity of NaCH3COO = mole/litre
= 0.076
Now,
NaCH3COO + H2O = NaCH3COOH + OH-
Initial 0.075 0 0
Eqm 0.075-x x x
Kb = [NaCH3COOH] [OH-] /[NaCH3COO]
Kw=Kb*ka here ka for given acid is = 1.8*10^-10 and kw= 10^-14 so kb= 5.6*10^-10
Therefore, 5.6*10^-10 = x^2/0.075 since 0.075-x = 0.075
So x= 6.48*10^-6
Now pOH = - Log[6.48*10^-6]
= 5.188
Therefore pH = 14-5.188
= 8.812 answer
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