Reference electrodes Standard Hydrogen electrode (SHE) has reduction potential of 0.00V by definition. Pressure is 1 atm and [H+]=1.00. SHE is theoretical, cannot actually be achieved because [H+]=1 cannot be achieved due to activities. A real life SHE must be corrected with the Nernst equation. Example: you have a hydrogen electrode at 720 torr and a pH of 4. What is the potential The reduction of hydrogen is: 2H+ + 2e- = H . 2 Using Nernst equation: 0 2 E = E – 0.0592/n*log(Q) = 0 – 0.0592/2*log((720/760)/(10^-4) ) = -0.236 V Remember to square the hydrogen concentration. Q expression is products over reactants raised to the balancing coefficients. Galvanic cell problems Calculating Kf for CuY given the following cell (Ka is 10^-7, Ecell = 0.5 V, Esilver = 0.799 V, Eanode = Ecathode – Ecell): Redox titration: Deviations Ecell = Ecathode – Eanode only holds true for ideal circumstances. It can deviate due to liquid junction potential (this deviation can be minimized by choosing an appropriate electrolyte), IR drop (caused by resistance within the battery itself, not present if current is not flowing) and polarization effects. Gas chromatography 2 Number of theoretical plates = 16 (Tr/w) . The more theoretical plates you have, the better peak separation you will have. The Van Deemter equation: H = A + B/μ + Cμ, where μ is the rate of flow of the carrier gas. A stands for eddy diffusion constant