Standard Hydrogen Electrode SHE explaination

standard hydrogen electrode SHE

1. STANDARD HYDROGEN ELECTRODE
A standard hydrogen electrode(SHE)consists of a
platinisedplatinum electrodeimmersed in a solution
of 1 moldm
-3
H
+
ions. Hydrogen gas at a pressure of 1
atmand 25
o
Cis bubbled over the platinum electrode.
The platinum electrode has a large surface area so that it can establish an
equilibrium between H
2(g) and H
+
(aq) as rapidly as possible.
2 H
+
(aq)+ 2 e
−
H
2
(g)

2. •Standardreductionpotential(orstandardelectrode
potential)isthevoltageassociatedwithareduction
reactionatanelectrodewhenallsolutionsare1Mand
allgasesareat1atm.
•Itisimpossibletoobtainthestandardelectrodepotential
ofasinglehalfcellbecauseonlydifferencesinpotentials
aremeasureable.
•Standardreductionpotential(S.R.P)valuesorE
o
redof
half-cellsarereferencedtoaStandardHydrogen
Electrode(SHE).
•Thestandardreductionpotentialforhydrogenis0V:
2H
+
(aq,1M)+2e
−
H
2(g,1atm)
•SHEactsaseithercathodeoranodewhenconnectedto
otherhalf-cells.

3. Cathode (+)
Anode (-)
Determination of E
o
redofZn
2+
(aq)/Zn(s) half-cell
Zn
2+
(aq)/Zn(s) half-cell is is anode and SHEis cathode.

4. Cathode (+)
Anode (-)
SHE is anode and Cu
2+
(aq)/Cu(s) half-cell is cathode.
Determination of E
o
redofCu
2+
(aq)/Cu(s) half-cell

5. E
o
redofCu
2+
(aq)/Cu half-cell and Zn
2+
(aq)/Zn half-cell
can be calculated by substituting the cell voltage (or
standard cell potential) measured by the voltmeter
into the following formula:

6. Zn
2+
(aq) + 2e
-
Zn(s)
Cu
2+
(aq) + 2e
-
Cu(s)
E
o
= -0.76 V
E
o
= + 0.34 V
2H
+
(aq) + 2e
-
H
2(g)E
o
= 0.00 V
E
H /H = 0.00 V+
o
2
o
E = -0.76V
Zn
2+
/Zn
E
Cu/ Cu
= + 0.34V2+
o Standardreduction
potential(S.R.P)or
standardelectrode
potential