PCH241P MAYIJUNE 2017 Question 5 (a) How do we distinguish between two metals (e

Question

PCH241P MAYIJUNE 2017 Question 5 (a) How do we distinguish between two metals (electrodes) in a ell redox reaction According to your answer, which one is the cathode, and which one is the anode? (b) Calculate the standard reaction potental (E®) of the following cells (u) Cd2+ + V ? Cd + V2. (c) The CN concentration of 20 0mL of a NaCN solution was determined by ttration The endpoint was reached after 300s with a current of 16 5mA The H ion is generated by the reaction 2H2O ? O2(g) + 4H+ + 4e. NaCNH eNa(s)+ HCN Calculate the number of grams of NaCN per litre of solution [15]

Explanation / Answer

Ans 5

Part a

Two metals in redox reaction

One metal is being oxidized and another metal is being reduced.

Oxidation numbers of metal increases from reactants to products, it is oxidation reaction

Oxidation reaction occurs at anode

Oxidation numbers of metal decreases from reactants to products, it is reduction reaction

Reduction reaction occurs at cathode

Part b

I) The two half cell reactions are

Oxidation reaction at anode

Fe2+ = Fe3+ + e-

Eox = - 0.77 V

Reduction reaction at cathode

Ag+ + e- = Ag

Ered = 0.80 V

Overall cell reaction

Fe2+ + Ag+ = Fe3+ + Ag

Standard reduction potential

E°cell = Eox + Ered

= - 0.77 + 0.80

= 0.03 V

II)

The two half cell reactions are

Oxidation reaction at anode

V = V2+ + 2e-

Eox = 1.19 V

Reduction reaction at cathode

Cd2+ + 2e- = Cd

Ered = - 0.40 V

Overall cell reaction

Cd2+ + V = Cd + V2+

Standard reduction potential

E°cell = Eox + Ered

= 1.19 - 0.40

= 0.79 V

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