Solutions with a wide range of Hg²⁺ concentrations were prepared to calibrate an experimental Hg²⁺ ion-selective electrode. For the range 10 ^-5 < [Hg²⁺] [< 10^-1 M, Hg(NO³)² was used directly. The range 10^-11 <[Hg²⁺] < 10^-6 M could be covered by the buffer system HgCl₂(s) + KCl(aq) (based on pK_sp for HgCl₂ = 13.16). The range 10^-15 < [Hg²⁺] < 10^-11 M was obtained with HgBr₂(s) + KBr(aq) (based on pKsp for HgBr₂ = 17.43). The resulting calibration curve is shown in the figure. Calibration points for the HgCl₂/ KCl buffer are not in line with the other data. Suggest a possible explanation.

Transcribed Image Text:

500 400 HgCl, Hg(NO)2 KCI 300 200 HgBr, 100 KBr -15 -10 -5 --0 log(Hg") E(mV vs. S.C.E.)