Omega PHB21, User Manual

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7
4.
MV Measurement
In order to measure potential redox it is used metallic electrodes, generally Platinum or Silver. This type of
electrode refers to chemical reactions in solutions that operate only by electrons transference. Such reactions
occur with composed elements presenting two or more oxidizing stages. Ex.: Fe2+ / Fe3+. The redox
measurement applications in a determined process, complies with previous knowledge of certain factors:
presence of infectants capable of competing with the main redox reaction, approximate values of the ions activity
coefficients entering the final equation of the potential differential, approximate speed of the reaction to be
controlled, necessary or not to control the pH. At Oxide reduction systems where the ions H+ take part at the
reaction, the redox potential depends on the pH. In order to obtain a complete description of such systems it is
necessary to indicate, besides the reference electrode, the pH value. The temperature has two effects over the
redox potential. First it enters as a factor over the logarithem of
equation. This means that a determined
reason of the ionic activity, the electrode will develop a different potential. Second, the temperature influence the
Ionic activity on each ion of the solution.
NERNST
Oxide Redox Potential Measurement