1)求弱酸的离解常数
pH=pKa+lg(碱的摩尔/酸的摩尔)
4.3=pKa+lg[(41.20x0.09-8.24x0.363)/(8.24x0.363)]
4.3=pKa-0.62
pKa=4.9
Ka=1.2x10^-5
2) 求计量点的PH值
NaOH滴定至计量点时,溶液体积=50.00+41.20=91.20 mL,
所以,弱酸根的浓度=41.20x0.09/91.20=0.04066 mol/L
水解平衡,有
Kb=Kw/Ka=1x10^-14/1.2x10^-5=8.33x10^-10=[OH-]^2/(0.04066-OH-])
[OH-]=5.8x10^-6 mol/L
pH=8.76