计算在ph=3.0,含未配位的EDTA总浓度为0.1mol/L时,Fe3+/Fe2+电对的条件电位（忽略离子强度的影响）.Fe3+/Fe2+电对的标准电极电势是0.771V

Question

计算在ph=3.0,含未配位的EDTA总浓度为0.1mol/L时,Fe3+/Fe2+电对的条件电位（忽略离子强度的影响）.Fe3+/Fe2+电对的标准电极电势是0.771V

Answer 1

pH=3.0, a= [Y4-]/EDTA= 2.51x10^-11
Kf'([FeY]-1)=a x Kf([FeY]-1)= 2.51x10^-11 x 1.3x10^25 =3.25x10^14
Kf'([FeY]-2)=a x Kf([FeY]-2)= 2.51x10^-11 x 2.1x10^14 =5.27x10^3
因为
Kf'([FeY]-1)={[FeY]-1}/[Fe3+]EDTA] ===> [Fe3+]={[FeY]-1}/Kf'([FeY]-1)[EDTA] ={[FeY]-1}/3.25x10^13
Kf'([FeY]-2)={[FeY]-2}/[Fe2+]EDTA] ===> [Fe2+]={[FeY]-2}/Kf'([FeY]-2)[EDTA] ={[FeY]-2}/5.27x10^2
所以,
E=E0 + 0.05916log(Fe3+/Fe2+)=0.771 + 0.05916log({[FeY]-1}/3.25x10^13/{[FeY]-2}/5.27x10^2)
=0.771 + 0.05916log(5.27x10^2/3.25x10^13) + 0.05916log({[FeY]-1}/{[FeY]-2})
=0.771-0.638+0.05916log({[FeY]-1}/{[FeY]-2})
=0.133+0.05916log({[FeY]-1}/{[FeY]-2})
所以,在标准状态下,条件标准电位 E0({[FeY]-1}/{[FeY]-2})=0.133 V