Name____Answer Key_______________________
Quiz 8 (10 pts)
CEM 434
Fall 2015
1. (2 pts). Name and briefly describe the two types of electroanalytical methods that were discussed on
Wednesday?
Potentiometric methods involve an indicator electrode and a reference electrode. The stable potential
of the indicator electrode relative to the reference electrode is measured (zero current) and this
potential can be related to (in principle) to an activity of an analyte at the surface. Selectivity can be
introduced by chemical modification of the indicator electrode surface or by using permselectivive
membranes. Molecules, ions and gases can be detected. Voltammetric methods involve applying a
controlled potential to a working electrode and measuring the current that flows between the working
and counter electrodes. The measured current can be related (in principle) to the concentration of
analyte near the electrode surface undergoing oxidation or reduction.
2. (2 pts). A Cu electrode was placed in contact with a solution containing 3.25 mM Cu(NO 3)2 at room
temperature. What is the potential of this electrode on the hydrogen reference scale (NHE) at
equilibrium?
Cu+2 + 2e- = Cus Eo = 0.34 V vs. NHE (hydrogen scale) First steps: (i) always write the redox reaction(s)
and (ii) look up standard reduction potential(s) (Eo) from a table.
3. (2 pts). What is Ecell for this electrochemical cell: Cu/[Cu+2]=1M//[Ag+]=1M/Ag.
Ec (cathode potential, right)….
Ea (anode potential, left)……..
Ag+ + e- = Ags
Cu+2 + 2e- = Cus
Eo = 0.799 V (vs. NHE)
Eo = 0.34 V (vs. NHE)
4. (4 pts). What is Ecell and ΔG for the following electrochemical cell:
Cu/[Cu+2]=1.65 mM//[Zn+2]=0.56 mM/Zn
Ec (cathode potential, right)….
Ea (anode potential, left)……..
Zn+2 + 2e- = Zns
Cu+2 + 2e- = Cus
Eo = - 0.763 V (vs. NHE)
Eo = 0.34 V (vs. NHE)