Write the half-reactions of an electrochemical cell whose overall reaction is Ag

Question

Write the half-reactions of an electrochemical cell whose overall reaction is AgCl rightarrow Ag^+ + Cl^-. How is Q for this cell related to the K_sp of AgCl? If you know the numerical value of the Ksp of AgCl and the molarity of the silver ion, explain how the cell could be used to determine the chloride ion molarity of an unknown solution that contains chloride ion. How would the cell potential of the cell change if lead(II) nitrate is added to the cathode compartment? You may look up any constants you wish.

Explanation / Answer

a)

AgCl <--> Ag+ and Cl-

For... Q

Q = [Ag+][Cl-]

clearly

Q = Ksp in this specific case!

b)

apply nerst equation

Ecell = E°cell - 0.0592/n * log(Q)

and Q = [Ag+][Cl-] = Ksp

so

Ecell = E°cell - 0.0592/n * log(Q)

Ecell --> can be measured, E°cell --> can be calculated, n = 1 mol fo e- transferred

Q = [Ag+] is known, and Ksp is also known, simply solve for Cl-

c)

Pb(NO3)2 --> Pb+2 and NO3-

note that Pb+2 + 2Cl-(aq) --> PbCl2(s)

so... Cl decreases, it is a requirement so... Ecell decreases

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