每日一句 This university is not simply turning out specialists, it is preparing citizens. And citizens are not spectators in the affairs of their country. They are participant in its future. G. W. Bush, Address at Tsinghua University

Our Goals (1) Calculate unknown potential from given potentials (2) The principle for electroanalysis through potential measurement; (3) Construction and application of Pourbaix diagram.

2) influential factor of E j Pt(s), H 2 (g,p)  HCl(m)  HCl(m′)  H 2 (g, p), Pt(s) E j On passage of 1 mole of electrons through the cell, t + mol H + and t  mol Cl  pass the boundary For uni-univalence electrolytes

4) requirements of salt bridge electrolyte 1)does not react with either solution 2)transference number of cation and anion is close 3)of high concentration. ionsK+K+ NH 4 + Cl  NO 3  10 2 /S·m 2 ·mol t + of some common salt bridge electrolytes c/mol·dm KCl NH 4 Cl0.491 KNO

c/mol·dm EjEj Concentration-dependence of E j Why does salt bridge reduce the junction potential

5) Effects of salt bridge: 6) Elimination of junction potential

Chapter 7 Electrochemistry §7.9 Electrode potential and electromotive forces

1) emf’s and  r G m of a reaction in different forms reaction: H 2 + Cu 2+  Cu + 2H +  G 1, E 1 1/2 H 2 + 1/2 Cu 2+  1/2 Cu + H +  G 2, E 2 Cu + 2H +  H 2 + Cu 2+  G 3, E Influential factors of electrode potential Exercise: Compare  G 1,  G 2,  G 3 and E 1, E 2, E 3.

2)  between different oxidation states Fe 3+ Fe 2+ Fe Give the relationship between  Exercise Initial state and final state

AgCl = Ag + + Cl - Ag(s)|AgNO 3 (c 1 ) ||KCl(c 2 ) |AgCl(s)|Ag(s) 3)  of relevant electrodes Exercise: deduce the relationship betweenand

Concentration-dependence of  Nernst equation for Ag + /Ag electrode  (Ag + /Ag) depends on [Ag + ], or  (Ag + /Ag) responds to [Ag + ]. The relationship between  (Ag + /Ag) and [Ag + ] can be used for quantitative electroanalysis of Ag +.

Can we use hydrogen electrode for measuring the pH of the solution? Give the principle of the measurement. Exercise: why electrode Hg(l)  Hg 2 SO 4 (s)  CaSO 4 (s)  Ca 2+ (m) can be used to measure the concentration of Ca 2+ in a solution? Normal and italic

pH-dependence of  : Pourbaix diagram For electrode reaction with H + or OH - participating in, the electrode potential will depend on pH. O 2 + 4H + + 4e -  2H 2 O  =  ⊖ lga H + = pH  =  ⊖ lga H + = pH 2H + + 2e -  H 2 pH-potential diagram/Pourbaix diagram H2OH2O O2O2 H2H2 pH  / V

Marcel Pourbaix, “Atlas of electrochemical equilibria in aqueous solutions”, National Association of Corrosion Engineers, Marcel Pourbaix (1904– 1998), a Russian-born, Belgian chemist.

Construction of Pourbaix diagram Cu 2+ Cu(OH) 2 Cu pH  / V CuO 2 2  Cu 2 O

Group discussion -2 1)How can you measure the liquid-liquid junction potential of a HCl/KCl interface? Write out the notation of the cell you use to conduct your measurement. 2)A potential is usually established across the cell membrane due to the concentration difference of K + inside and outside a cell, which is named as membrane potential. This potential is crucial for sensation of any living thing. Can you design an experimental apparatus for measuring the membrane potential of a cell? State the principle you use.