Electroanalytical Chemistry Lecture #2
Electroanalytical Chemistry Lecture #2
An interfacial Process For o+ne=R 5 separate events must occur O must be successfully transported from bulk solution(mass transport) O must adsorb transiently onto electrode surface (non-faradaic) CT must occur between electrode ando (faradaic) R must desorb from electrode surface(non faradaic) R must be transported away from electrode surface back into bulk solution(mass transport)
An Interfacial Process • For: O + ne- = R • 5 separate events must occur: – O must be successfully transported from bulk solution (mass transport) – O must adsorb transiently onto electrode surface (non-faradaic) – CT must occur between electrode and O (faradaic) – R must desorb from electrode surface (nonfaradaic) – R must be transported away from electrode surface back into bulk solution (mass transport)
What is an electrode Electrical double layer
What is an Electrode? • Electrical double layer
Electrode classification Based on the nature and number of phases between which electron transfer occurs 3 Classes Electrodes of the first Kind Electrodes of the second Kind Electrodes of the third Kind
Electrode Classification • Based on the nature and number of phases between which electron transfer occurs • 3 Classes: – Electrodes of the First Kind – Electrodes of the Second Kind – Electrodes of the Third Kind
Electrode of the first Kind Metal in contact with its cations or non- metal in contact with its anions EXAMPLES Cu2+ /Cu(s) Electrodes in daniell cell Zn2/Zn(s SHE Ag/Ag(nonaqueous reference electrode) CI/Cl(g/Pt
Electrode of the First Kind • Metal in contact with its cations or nonmetal in contact with its anions • EXAMPLES: – Cu2+ /Cu(s) – Zn2+/Zn(s) – SHE – Ag+ /Ag (nonaqueous reference electrode) – Cl- /Cl2 (g)/Pt Electrodes in Daniell cell
Electrode of the first kind (cont'd) Electrode response given by Nernst equation(Nernstian) E=EO+(rT/nF)In a(M2t) NoTE Fe al and w electrodes are Not electrodes of the first Kind these have relatively thick surface oxide coatings
Electrode of the First Kind (cont’d) • Electrode response given by Nernst equation (Nernstian): – E = E0 + (RT/nF) ln a(M2+) • NOTE: Fe, Al, and W electrodes are NOT electrodes of the First Kind – these have relatively thick surface oxide coatings
Electrode of the second Kind Metal in contact with sparingly soluble salt of the metal Common name: anion electrodes EXAMPLES Ag/AgCl(s) Hg/Hg, Cl(s)/cl(saturated calomel electrode SCE)
Electrode of the Second Kind • Metal in contact with sparingly soluble salt of the metal • Common name: anion electrodes • EXAMPLES: – Ag/AgCl(s) – Hg/Hg2Cl2 (s)/Cl- (saturated calomel electrode; SCE)
Electrode of the second Kind Electrode response given by E=E0-(RT/FIn a(cr) NOTES anion activity determines potential make great reference electrodes because of low solubility of salt(potential very stable)
Electrode of the Second Kind • Electrode response given by: • E = E0 - (RT/F) ln a(Cl- ) • NOTES: – anion activity determines potential – make great reference electrodes because of low solubility of salt (potential very stable)
The Calomel reference electrode Electrode Acronym Potential vs SHE Hg(/Hg2Cl2(s)KCI(0. 1 M) 0.3337 Hg/Hg2Cl2(s)/KCl(1 M) NCE 0.2801 Hg(/Hg2Cl2(s)/KCl(sat'd) SCE 0.2412 Hg(/Hg2 Cl2(s)NaCl(sat'd) SSCE 0.2360 Note: concentrations typically high = A concentrations small electrode doesn t become polarized potential constant
The Calomel Reference Electrode Electrode Acronym Potential vs. SHE Hg(l)/Hg2Cl2 (s)/KCl (0.1 M) 0.3337 Hg/Hg2Cl2 (s)/KCl (1 M) NCE 0.2801 Hg(l)/Hg2Cl2 (s)/KCl (sat'd) SCE 0.2412 Hg(l)/Hg2Cl2 (s)/ NaCl (sat'd) SSCE 0.2360 Note: concentrations typically high concentrations small electrode doesn’t become polarized potential constant