Although the hydrogen electrode may be conceptually the simplest electrode and is the basis for our reference state of electrical potential in electrochemical systems, it is cumbersome to use. Therefore, several substitutes for it have been devised. One of these alternatives is the quinhydrone electrode (quinhydrone, Q .QH2, is a complex of quinine, C6H402 = Q, and hydroquinone, C6H4O2H2 = QH2). The electrode half-reaction is Q (aq) + 2 H+ (aq) + 2 e- → QH2(aq), EΘ= +0.6994 V. If the cell Hg | Hg2CI2(s) | HCI (aq) | Q• QH2 | Au is prepared, and the measured cell potential is +0.190 V, what is the pH of the HCI solution? Assume that the Debye-Huckel limiting law is applicable.