Quinhydrone is a sparingly soluble one-to-one addition compound formed from hydroquinone and quinone. When solid quinhydrone is dissolved in an aqueous medium, equal concentrations of hydroquinone and quinone result. If a platinum wire is dippled into the solution, the potential of the electrode is govern by the reversible reaction:

Where Q denotes quinone and H₂Q denotes hydroquinone. The E° value of this half cell reaction is +0.46 V with respect to the saturated calomel reference electrode (SCE). Because the potential of the quinone-hydroquinone half reaction depends on the concentration of hydrogen ion, it is possible to use this system to measure pH. A sample solution of unknown pH was saturated with quinhydrone and a platinum electrode was dipped into it. If the potential of the such electrode was found to be +0.22 V with respect to SCE, what was the pH of the sample solution?
[Given : $\frac{2.303\mathrm{RT}}{\mathrm{F}}=0.06$]