An electrochemical cell consists of a standard hydrogen electrode and a copper m

Question

An electrochemical cell consists of a standard hydrogen electrode and a copper metal electrode. What is the potential of the cell at 25 degree C if the copper electrode is placed in a solution in which [Cu^2+] = 2.5 Times 10^-4 M? If the copper electrode is placed in a solution of 0.10 M NaOH that is saturated with Cu(OH)_2, what is the cell potential at 25 degree C? K_SP = 1.6 Times 10^-19. The copper electrode is placed in a solution of unknown [Cu^2+]. The measured potential at 25 degree C is 0.195 V. What is [Cu^2+]?

Explanation / Answer

The reaction that takes place is Cu+2+2e---->Cu Eo= 0.34V

n= 2 in this case ( number of electrons exchanged)

From E = Eo' + (2.303RT/nF)log[Ox]/[Red]. = Eo+(0.0592/2) log (2.5*10-4) =0.34-0.11=0.23V

b) NaOH----> Na+ +OH-

Since NaOH ionizes completely [OH] =0.1M

Cu(OH)2 ---->Cu+ +2OH-

Cu+2= x [OH] =2x

at Equilibrium Cu+2= x and [OH-] = 0.1+2x

KSp = (0.1+2x)2*x= 1.6*10-19

solver can be used to solve thsi problem by assuming some value of x and matching LHS and RHS

x= 1.6*10-17

Cu+2= 1.6*10-17

E= 0.34+(0.0592/2)log(1.6*10-17) =-0.15716V

C) E= Eo+(0.0592/2)log(Cu+2)

0.195= 0.34 +0.0296 log(Cu+2)

Cu+2 = 5.98*10-5M

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