In 2000, Ceresa, Pretsch, and Bakker 1 published a paper

In 2000, Ceresa, Pretsch, and Bakker ¹ published a paper titled “Direct Potentiometric Information on Total Ionic Concentrations” . In this paper they investigated the use of three ion-selective electrodes to determine the concentration of calcium in solutions.

Retrieve the paper and answer the questions below:

1. Describe the main similarities and differences between the three electrodes.
2. Determine (using appropriate equations), the concentration, ionic strength and the activity for Ca ²⁺ in the electrode labeled “ ISE with Ca ²⁺ uptake ”.
3. Table 1, 2 and 3 report the data collected with electrode 1,2 and 3 respectively.
   1. Plot the cell potential vs -log(a _Ca 2+ ) for the three electrodes.
   2. Determine the value at which the plot deviates more than 5% from linearity.
   3. Determine the slope and intercept of the linear part of each plot.
   4. We can model a cation-selective electrode with the equation

E _cell = K − [(0.0592/n) * pX]

Where K is a constant, n is the number of moles of electron involved and pX =

−log ( a _X ) with X being a cation.

Do the plots follow this equation? Compare and discuss.

4. The researchers use the term “super-nerstian” in the article. Explain why.
5. Critically discuss the significance of the results obtained in this study.

Table 1: Data for electrode 1

Table 2: Data for electrode 2