Consider an electrochemical cell involving the overall reaction 2AgBr(s) + Pb(s) $\rarr$ Pb²⁺ + 2Ag(s) + 2Br^-
Each half-reaction is carried out in a separate compartment.The anion included in the lead half-cell is NO₃^-.The cation in the silver half-cell is K⁺.The two half-cells are connected by a KNO₃ salt bridge.If [Pb²⁺] = 1.0 M, what concentration of Br^- ion will produce a cell emf of 0.25 V at 298 K?
Given: AgBr(s) + e^- $\rarr$ Ag + Br^-, E° = +0.07 V.

Question

Consider an electrochemical cell involving the overall reaction 2AgBr(s) + Pb(s)

\rarr

Pb²⁺ + 2Ag(s) + 2Br^-
Each half-reaction is carried out in a separate compartment.The anion included in the lead half-cell is NO₃^-.The cation in the silver half-cell is K⁺.The two half-cells are connected by a KNO₃ salt bridge.If [Pb²⁺] = 1.0 M, what concentration of Br^- ion will produce a cell emf of 0.25 V at 298 K?
Given: AgBr(s) + e^-

\rarr

Ag + Br^-, E° = +0.07 V.

Quizplus · Accepted Answer

First, we need to write the balanced overall reaction:

2AgBr(s) + Pb(s) → PbS(s) + 2Ag(s) + 2Br^-(aq)

The reduction half-reaction occurring in the silver half-cell is:

AgBr(s) + e^- → Ag(s) + Br^-(aq)

The standard reduction potential for this half-reaction is given as +0.07V.

The oxidation half-reaction occurring in the lead half-cell is:

Pb(s) + Br^-(aq) → PbBr(s) + e^-

The standard reduction potential for this half-reaction can be calculated using the standard reduction potential for the reduction half-reaction:

E°cell = E°reduction + E°oxidation

0.25V = 0.07V - E°oxidation

E°oxidation = -0.18V

The Nernst equation relates the cell emf to the concentrations of the species involved:

Ecell = E°cell - (RT/nF) ln Q

At 298K, R=8.314 J/(mol*K), F=96,485 C/mol, and n=2 for this reaction.

Q = [Pb2+][Br^-]^2/[Ag+][Br^-]^2

We are given that [Pb2+] = 1.0M. Let x be the concentration of Br^- required:

0.25V = 0.07V - (RT/2F) ln ([1.0][x]^2/[0.14][x]^2)

Solving for x gives x = 0.14 M. Therefore, the answer is B) 0.14 M.

Consider an Electrochemical Cell Involving the Overall Reaction 2AgBr(s)+ Pb(s) →\rarr→

Consider an Electrochemical Cell Involving the Overall Reaction 2AgBr(s)+ Pb(s) $\rarr$