Quinhydrone Electrode and pH Determination

Quinhydrone Electrode and pH Determination

Quinhydrone Electrode and pH Determination

Quinhydrone Electrode

Quinone + Hydroquinone = Quinhydrone
The foloowing half cell reaction takes place between quinone and hydroquinone in the presence of H+ ion-
quinhydrone electrode
This electrode is easy to set up and small amount of solution required for measurement. It gives accurate pH between 0 to 9. In alkaline solution, the pH values are not accurate due to ionization and aerial oxidation of QH2.

pH Determination

For pH determination, it is kept in the solution whose pH is to be determined and connected to a calomel electrode. Hence the cell is represented as-
(−),Pt,Hg|Hg2Cl2(s),KCl sat. solution || Solution of unknown pH,Q|QH2Pt(+)
Therefore, the emf of cell is given by-
Ecell = − 0.2415 − (−0.69994 + 0.0591 pH)
or, Ecell = − 0.2415 + 0.69994 − 0.0591 pH
or, 0.0591 pH = 0.4579 − Ecell
or, pH = (0.4579 − Ecell)/0.0591
By Knowing the value of emf of the cell, pH of the solution can easily be calculated.

Glass Electrode for pH Measurement