ID: A . Cadmium is a toxic heavy metal. The U.S. Environmental Protection Agency

Question

ID: A . 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 drinking water using a voltaic cell based on the following half-reactions. Ag (ag)+e Ag(s) 0.7996 v Cd2 (ag)+ 2ed(s)0.4030 v If the silver ion concentration were 1.000 M, what cadmium ion concentration at 298 K would increase the cell potential by 10 mV from the standard cell potential? a. 0.36 M b. 4.6 M d. 0.68 M e. 6.8 M c 0.46 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+] /1.00 = 0.4594

[Cd2+] = 0.4594 x 1.00 = 0.459

[Cd2+] = 0.46 M

Option C is the correct answer

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