Consider the cell described by this reaction 3Hg2+(aq) + 2Cr(s) 3Hg(I) +2Cr3+(aq
ID: 591967 • Letter: C
Question
Consider the cell described by this reaction 3Hg2+(aq) + 2Cr(s) 3Hg(I) +2Cr3+(aq) . Calculate the cell potential wh en [Hg2+] is 5.90×10-4 M and [Cr3+] is 1.47 M ? E= 1.496. Draw the line diagram for the cell For the following cell Cu | Cu2(0.0100M) II Fe2(0.100 M),F3 (0.0200M) | Pt 1. 2. Write the chemical reaction Compute the potential 3. For the following cell " 3Cu""(aq) + 2Al(s) 3Cu(s) + 2AP"(aq) . If [Cu 1.26 M and Ecell is measured to be 2.060V, calculate [Al3+] 4. A concentration cell is made with two nickel half-cells with concentrations of 1.00 M and 1.00x10-4 M. Calculate the potential of the cell. (don't need E for Niz)Explanation / Answer
Q1
When the cell is NOT under standard conditions, i.e. 1M of each reactants at T = 25°C and P = 1 atm; then we must use Nernst Equation.
The equation relates E°cell, number of electrons transferred, charge of 1 mol of electron to Faraday and finally, the Quotient retio between products/reactants
The Nernst Equation:
Ecell = E0cell - (RT/nF) x lnQ
In which:
Ecell = non-standard value
E° or E0cell or E°cell or EMF = Standard EMF: standard cell potential
R is the gas constant (8.3145 J/mol-K)
T is the absolute temperature = 298 K
n is the number of moles of electrons transferred by the cell's reaction
F is Faraday's constant = 96485.337 C/mol or typically 96500 C/mol
Q is the reaction quotient, where
Q = [C]^c * [D]^d / [A]^a*[B]^b
pure solids and pure liquids are not included. Also note that if we use partial pressure (for gases)
Q = P-A^a / (P-B)^b
substitute in Nernst Equation:
Ecell = E° - (RT/nF) x lnQ
Ecell = 1.496 -8.3614*298/(2*6*96500) * ln( [ Cr+3]^2 / [Hg+2]^3)
Ecell = 1.496 -8.3614*298/(2*6*96500) * ln( (1.47^2)/(5.9*10^-4)^3)
Ecell = 1.4463 V