Parameters to Indicate Redox Conditions

The measurement of redox conditions by means of a cell voltage, where one electrode has a fixed reference potential and the other is expected to react reversibly with natural systems, is attended by a number of problems. The platinum electrode only works well under certain conditions, it is difficult to get the electrode into 

Eh has been important in both the measuring and reporting of redox conditions, but an argument can be made that it should be used only in the measurement and not the reporting of redox conditions, i.e., that however measurements are made, results should be reported as /o or log /02 values. There would be two advantages to this. First, the use of Eh entails the use of a relatively complex set of conventions, which are quite difficult to remember unless used continuously (see Appendix D for a complete comparison of conventions). Secondly, and more importantly, Eh is less useful than /o, because it is so commonly linked in reactions with pH (giving the Nemst slope ). This means that a value for Eh without an accompanying value for 

The conversion from an Eh-pH point to a log /oj value is very simple (equation 18.60). We have tried to show that the very low values of /oj generally obtained at low temperatures should not be a hindrance to its use, and we advocate its use in the reporting of any redox conditions. 

Water draining from abandoned coal mines causes considerable environmental damage because of its iron content and acidity. In an attempt to understand the chemistry of these waters, the following measurements were made in water in the Loree 2 shaft near Wilkes-Barre, PA. (Barnes et al., uses Prof. Paper 473-B, 1964). 

Samples 2 and 3 showed a yellow turbidity, the rest were clear. Samples 

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