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]]>ELECTRODE POTENTIAL:– Difference between the potential of two electrodes.
POTENTIOMETRY consists of measuring potential or emf of solution using set of indicator & reference electrode.
potential of solution depends on nature, concentration , temperature of ions of drug substance.
POTENTIAL AND CONCENTRATION – THE NERNST EQUATION:-
The potential of a metal electrode at 25°c immersed into a solution of its ions is given by
E=Eº+0.0591/n log[mn+]
where Eº = Standard potential of the metal
n = valency of ions
c= concentration of ions
TERMINOLOGY :-
TYPES OF ELECTRODES :-
A. Based on the components :-
B. Based on working principle :-
REFERENCE ELECTRODE :-
Hydrogen electrode is the primary standard against which the potentials of other electrodes are measured. it can be used as indicator as well as reference electrode. It consists of a platinum foil coated with platinum black and has wire contacts through mercury. This assembly is enclosed in a glass covering through which hydrogen is passed at 1 atmospheric pressure continuously and dipped into the solution of standard acid or unknown solution. At all time the electrodes surface and the solutions should be saturated with the gas.
the potential of this electrode is given as folloes:
E=Eº +0.0592 LOG[H+]
= Eº-0.0592
= -0.0592
MERITS :-
DEMERITS :-
E=-0.0591 pH
MCQ:-
1.which technique is used to measure emf ?
a. acid base titration
b. mass spectroscopy
c. TGC
d.potentiometry
2. which part of the cell is responsible to between two solution that allows the movement of current in the form of ionic charge ?
a. electode
b.platinum wire
c.salt bridge
d.none of the above
3.which device is converted physical or chemical energy to electrical energy ?
a.cell
b.galvonometer
c.ECG
d.none of the above
4.In hydrogen electrode which material are using coating of platinum foil ?
a. pb
b.copper
c.platinum black
d.iron
5. which is dis advantage of hydrogen electrodes?
a.It is primary reference standard against which potential of other electrode are measured.
b.Exhibit no salt error& used over entire pH range.
c.Used as reference electrode when dipped with std. acid solution & as indicator electrode when dipped into a sample solution.
d.Factor like purity of H2 , pressure of H2 affect potential of electrode.
ANSWER KEY
1.d
2.c
3.a
4.c
5.d
REFERENCE :-
TEXT BOOK OF PHARMACEUTICAL ANALYSIS OF THIRD EDITION OF DR. S. RAVI SANKAR (PAGE NO. 9.3-9.17)
The post POTENTIOMETRY: NERNST EQUATION & TYPES OF ELECTRODES and MCQ for GPAT, Pharmacist, Drug Inspector appeared first on Gpatindia: Pharmacy Jobs, Admissions, Scholarships, Conference,Grants, Exam Alerts.
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