c. 8.1 x 102 50. Cadmium is a toxic heavy metal. The U.S. Environmental Protecti

Question

c. 8.1 x 102 50. Cadmium is a toxic heavy metal. The U.S. Environmental Protection Agency limits the concentration of cadmium ions in drinking water to less than 4 x 10* M. Assess the feasibility of monitoring of cadmium in drinking water using a voltaic cell based on the following half-reactions. Ag (aq)+eAg) Cd (aq)+2eCds) E"-+0.7996 V Fo-0.4030 V Iver ion concentration were 0.100 M, what cadmium ion concentration at 298 K would increase the cell potential by 10 mV from the standard cell potential? a. 3.6 x 10M b. 4.6 x 102M d. 6.8 x 10 M e, 6.8 × 10-2 M 4.6 × 10-3 M

Explanation / Answer

Overall cell reaction

Ag+ + Cd = Ag + Cd2+

From the Nernst equation at 298K

E = E°cell - (0.0592/2) log [Cd2+] /[Ag+]

E - E°cell = - (0.0592/2) log [Cd2+] /[Ag+]

10 mV x 1V/1000 mV = - (0.0592/2) log [Cd2+] /[Ag+]

- 0.01 x 2/0.0592 = log[Cd2+] /[Ag+]

-0.3378 = log[Cd2+] /[Ag+]

[Cd2+] /[Ag+] = 0.4594

[Cd2+] /0.100 = 0.4594

[Cd2+] = 0.4594 x 0.100 = 0.0459

[Cd2+] = 4.59 * 10^-2 M = 4.6*10^-2 M

Option B is the correct answer

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