解:首先求计量点pH,在计量点,所有的NH3全部变成NH4+,这是一个一元酸,
ka=Kw/Kb=(10^-14.00)/(10^-4.74)=10^-9.26;
判别式全部满足,使用最简式
[H+]=(CKa)^0.5=(0.0500×10^-9.26)=10^-5.28
pH=5.28
ΔpH=pH(终)-pH(计)=4.00-5.28=-1.28
TE=[(10^pH)-(10^-pH)]/[(CKt)^0.5]=[(10^pH)-(10^-pH)]/[(C/Ka)^0.5]
=[(10^-1.28)-(10^1.28)]/[(0.05/10^-9.26)^0.5]
=-0.20%