ANALYTICAL CHEMISTRY FINAL- ACS EXAM QUESTIONS AND ANSWERS A+ GRADED. BUY Quality Materials!
Potentiometry
an analytical method in which an electric potential difference (voltage) is measured
1. measurement of ion activity from the electric potential of an ion at an electrode surface
2. M...
Potentiometry
an analytical method in which an electric potential difference (voltage) is measured
1. measurement of ion activity from the electric potential of an ion at an electrode
surface
2. Msmt of potential difference between two electrodes of a galvanic cell at zero current
Redox titrations and electrode potential
-Reduction (adding e-) occurs at cathode (E+)
-Oxidation (removing e-) occurs at anode (E-)
Cell voltage = E+ - E-
Single line denotes phase boundary; double lines denote salt bridge.
Silver-Silver Chloride Reference Electrode (Ag|AgCl electrode)
half-reaction (written as reduction):
AgCl(s) + e- <--> Ag(s) + Cl-
-potential measured at anode (E-); Ag(s) | AgCl(s) | Cl-(aq) plus salt bridge
-problem: commonly, porous plugs become clogged causing a slow and unstable
electrical response.
S.C.E
saturated calomel electrode (calomel electrode saturated with KCl) is a reference
electrode, based on half reaction:
Hg2Cl2(s) + 2e- <--> 2Hg (l) + 2Cl-
and has potential denoted by E-
Indicator electrode
2 types:
1. Metal electrodes: develop elec pot in response to redox reaction at metal surface. Pt
is most common metal indicator electrode (inert).
-Example is Ag indicator electrode, which is just a solid Ag wire dipped into the solution.
The half-reaction is:
Ag+ + e- <--> Ag(s) V= E+ denoted by Ag | Ag+
E+ = E0(+) - .05916log(1/[Ag+]) = E0(+) + .05916log[Ag+]
**a silver electrode is also a halide electrode if solid silver halide is present, and [Ag+] =
Ksp/[X-]
2. ion-selective electrodes (ISEs) are indicator electrode that do not involve redox
processes, and have a membrane that specifically binds ion of interest. usually liquid-
based. electric potential difference (voltage) is measured across the membrane with 2
(inner and outer) reference electrodes. E = Eouter - Einner = constant + .05916/n(loga0)
where n is charge of analyte ion and a0 is its activity in the outer unknown solution.
** the glass electrode (pH electrode) most common ISE.
pH combination electrode
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