2, Calculate the electrode potential of the following half-cells. (1) Ag/Agl(s),

Question

2, Calculate the electrode potential of the following half-cells. (1) Ag/Agl(s), I. (0.015 M) (E degree Agl/AG = -0.151 V) (2) A silver wire placed in a solution that results from mixing 25.0 ml. of 0.0500 M Ag with 20.00 mL of 0.100 M KBr (E degree Ag/Ag = 0.799 V and E degree AgBr/Ag = 0.073 V) 3. Explain why two electrodes are used in potentiometry but three electrodes are used in voltammetry. 4. Explain the working principle of a rechargeable lead-acid battery, write the half-cell and full-cell reactions, and label the anode/cathode, +1- potential as well as the current/electron flow directions during discharging/charging processes. For a 12 V automotive battery, why six pairs of electrodes are used? 5. Explain the working principle of a pH meter. Why a new glass electrode must be soaked in water (electrolyte) for several hours before use? 6. Discuss the similarity and difference between a galvanic cell and an electrolyte cell in turns of e.g.. the name of the electrodes, flow directions of currents/electrons. oxidation/reduction reactions, positive/negative potentials. 7. Use cyclic voltammetry to distinguish the following redox processes: (a) reversible, (b) irreversible. (c) quasi-reversible, and (d) a reversible electrochemical process followed by a chemical reaction.

Explanation / Answer

Electrode reaction is

e--+ AgI --> Ag + I--

and   AgI ---> Ag + + I-    Ksp = 1 x 10-16

also E0 = 0.151 V

and Ksp = Ag+ I-

Ag = Ksp / I -

So-> E = E0 - 0.059 log Ksp / I -

E = 0.8 V - 0.059 log (10-16/ 0.151)

~~ 0.04 V

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