Quinhydrone electrode

hydroquinone

quinone

The quinhydrone electrode may be used to measure the hydrogen ion concentration (pH) of a solution containing an acidic substance.^[1]^[2]

A platinum wire electrode is immersed in a saturated aqueous solution of quinhydrone, in which there is the following equilibrium

C
₆H
₆O
₂ ⇌ C
₆H
₄O
₂ + 2H⁺ +2e⁻.

The potential difference between the platinum electrode and a reference electrode is dependent on the activity, $a_{H^{+}}$ , of hydrogen ions in the solution.

E=E^{0}+{\frac {RT}{2F}}\ln a_{H^{+}}

(Nernst equation)

The quinhydrone electrode provides an alternative to the most commonly used glass electrode.^[3] however, it is not reliable above pH 8 (at 298 K) and cannot be used with solutions that contain a strong oxidizing or reducing agent.^[1]

References[]

^ ^a ^b Bates, Roger G. Determination of pH: theory and practice. Wiley, 1973, pp 246-252
^ Rossotti, F. J. C.; Rossotti, H. (1961). The Determination of Stability Constants. McGraw-Hill., p 135
^ Vonau, W.; Guth, U (2006). "pH Monitoring: a review". Journal of Solid State Electrochemistry. 10 (9): 746–752. doi:10.1007/s10008-006-0120-4.

[Bates-1] Bates, Roger G. Determination of pH: theory and practice. Wiley, 1973, pp 246-252

[2] Rossotti, F. J. C.; Rossotti, H. (1961). The Determination of Stability Constants. McGraw-Hill., p 135

[3] Vonau, W.; Guth, U (2006). "pH Monitoring: a review". Journal of Solid State Electrochemistry. 10 (9): 746–752. doi:10.1007/s10008-006-0120-4.

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