Question

b) What weight % sulphur must be added to vulcanize polyisoprene (mer weight = 68) by crosslinking one half the possible sites. In this elastomer, each pair of mers has two possible crosslink sites. Assume three sulphur atoms are involved in each crosslink. Atomic weight: S-32 (10) 9. Copper and silver are in contact with an aqueous solution at 25°C containing Cu2+ and Ag* ions setting up a corrosion cell. a) Show the anode and cathode reactions. b) Now show the overall cell reaction. c) If [C?] =10°M and [Ag1=0.5M, calculate the cell voltage. Except for sign, standard electrode potentials are absolute. They do not change if you change the stoichiometry of the reaction. Electrode Reaction E° (V) Cu?* + 2e = Cu Age +e = Ag +0.34 +0.80 E=E°-2303RT log TE products dreactants 2.303RT -0.0592 V at T = 298°K

Answer 1

a) Half Reactions:-

Ag+ is gaining electrons thus is being reduced; reduction happens at the cathode

Ag⁺(aq)+e−⇌Ag(s)

Cu(s) is losing electrons thus being oxidized; oxidation occurs at the anode.

Cu(s)⇌Cu2⁺(aq)+2e−

b) 2Ag⁺(aq)+Cu(s)⇌Cu2⁺(aq)+2Ag(s)

c) E⁰cell = 0.80+(-0.34) = 0.46 V

  Ecell = 0.46 - (2.303RT/nF) log (10^-3 / 0.5^2)

  Ecell =0.46 - (0.0592/2)log(0.001/0.25) = 0.5309V

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