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pH Buffer Calculation Program (Demonstration)

Use this program to calculate the pH (total scale) of a TrisH+/Tris buffer in artificial seawater, the effects of varying the composition by adding or removing ions, and the uncertainties in the calculated quantities. For complete explanations of the model output, see the notes pages for the examples of a simple buffer (for which only section 1 should be filled in below), and a buffer with an altered composition (for which there must also be entries in section 2).

Fill in the form below (blanks in section 2 will be treated as zero), and press the Submit button.

1. Enter the temperature (0 to 45 oC), and the salinity (3 to 40)

Temperature (oC):      Salinity:


2. Vary the composition of the seawater, if needed

Vary Na+ by (%):   as:              Vary Mg2+ by (%):   as:
Vary Ca2+ by (%):   as:              Vary K+ by (%):   as:
Vary Cl− by (%):   as:              Vary SO42− by (%):   as:

There are limits to the percentages that can be entered here. For example, if the moles of Cl− in the buffer are reduced by removing KCl, then the percentage reduction in Cl- is limited by the fact that for every mole of total Cl− in solution there are only 0.0186 moles of K+. Therefore the greatest reduction that can be achieved in this way is only 1.86%. The mole ratios of the ions in the buffer, relative to Cl− = 1.0, are: Na+ = 0.784, Mg2+ = 0.0962, Ca2+ = 0.0189, K+ = 0.0186, SO42− = 0.0514.



Results will be displayed below. Click here:    (allow up to 10 secs for a result)

Notes

The model used for these calculations was produced for demonstration purposes, and is still a work in progress. Hence, the uncertainties in the ion-ion interactions are estimates (generally pessimistic ones) but, more important, some interactions are not yet included. If you would like to know more, please contact the author (s.clegg@uea.ac.uk).