1) Suppose that the diffusion current in a polarogram for reduction of Cd2+ at a

Question

1) Suppose that the diffusion current in a polarogram for reduction of Cd2+ at a mercury electrode is 19 µA. If the solution contains 25 mL of 0.50 mM Cd2+, what percentage of Cd2+ is reduced in the 3.6 min required to scan from 0.6 to 1.2 V?

2)A certain drug gives a polarographic wave with E1/2 = 0.240 V (versus S.C.E.) in 0.05 M H2SO4. A 50.0-mL sample containing the drug gave a wave height of 0.33 µA.When 2.00 mL of 2.94 mM of the drug in 0.05 M H2SO4 were added to the sample, the wave height increased to 0.78 µA. Find the molarity of the drug in the unknown.

Explanation / Answer

Let the molarity of the sample unknown be X M.

50.0 mL of X M 0.050 X moles.
2 mL of 2.94 mM sample contains: 2x10-3 * 2.94x10-3 = 5.88x10-6 moles

The number of moles of unknown in the sample are directly proportional to the wave height so:
5.88x10-6 + 0.050x / 0.050x = 0.78/0.33
5.88x10-6 + 0.05x = (0.78/0.33)*0.050x
5.88x10-6 + 0.05x = 0.1182x
5.88x10-6 = 0.1182x-0.05x
x = 8.62x10-5 M

I have a doubt with the question 1, but here's the second at least. Hope this helps

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