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STANDARD REFERENCE

ELECTRODES,PRINCIPLES,WORKING &

COMPARISION

PREPARED BY - PRAJAPATI MAULIK R.

ROLL NO. - 920

SUBJECT - ELECTRO METALLURGY & CORROSION.DEPARTMENT OF METALLURGY & MATERIAL

SCIENCE.

FACULTY OF TECHNOLOGY AND ENGINEERING

M.S. UNIVERSITY OF BARODA.

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They are electrodes which have stable & well-known electrode potential.

High stable electrode potential reached by redox

system with constant concentration.

Few aqueous reference electrodes & potential withrespect to S.H.E. e.g. Are,

1. S.H.E. E=0.0000V2. Saturated Calomel Electrode S.C.E. E=+0.242V

3. Copper Copper sulfate Electrode E=+0.318V

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4. Silver Chloride Electrode E=+0.225V

5. Glass electrode or pH-electrode

6. Palladium-Hydrogen electrode

The non-aqueous reference electrode is Quasi-Reference Electrode (QRE).

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Standard Hydrogen Electrode (SHE) also called asNormal Hydrogen Electrode (NHE).

Absolute electrode potential estimated to be 4.4V 4.6V.

Because of basis of comparison with all otherelectrode reactions, then declared to be zero.

Redox reaction, 2H + 2e H.

According to Nernst eq.E = RT/F ln( aH+/(pH2/p

0) 1/2)

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1. Platinized platinum electrode.

2. Hydrogen blow.

3. Solution of acid with activity of

H+

ion.4. Hydroseal for prevention of O2

interfearence.

5. Reservoir through which second

half element of galvanic cellattached.

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Saturated Calomel electrode (SCE) based on reactionbetween mercury & mercury chloride.

Electrode is normally linked via porous frit of salt

bridge which immersed in solution.E=E Hg22+

/Hg - RT/2F ln (Cl-)2

Potential of SCE is +0.244V (1N KCl).

Use In pH measurement , cyclic voltammetry &

electrochemistry. Silver/silver chloride also work same way.

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Outer body made ofglass.

Tip is porous frit.

Containing saturatedKcl solution.

At cental Hg Hg2clpast.

At top electricalcontact.

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It works on base of redox reaction copper & itssalt- copper sulfate.

Nernst equation given by,

E=0.337+RT/2Flnacu2+

Potential of electrode is +0.318V.

It is used in one of half cell in daniel Jakobigalvanic cell & copper coulometer.

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Commercial electrode isplastic tube holdingcopper rod & saturatedsolution of coppersulfate. Porous plug atend allows to contactto electrolyte.

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It is most commonly used for testing cathodicprotection control system in sea waterenvironment.

Redox reaction : Ag0 + cl- Agcl + e-

Ag0 + cl- Agcl + e-

Nernst equation given by,

E = E0 RT/F lnacl-

Standard potential of electrode is 23010mV.

However potential very sensitive to trace ofbromide ions which make it more negative.

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Outer body is ofglass.

Bottom ceramic ,

quartz or glassfiber junction.

Inside potessiumchloride solution.

Contected withsilverchloride salt &wire of silver.

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It is made from glass having special composition.

Mainly two types of glass,

1. Silicate : having Sio2 (matrix) & Li, Na , K, Al ,etc.

2. Chlcogenide : having molecules of AsS, AsSe,etc. Potential of electrode given by Nikolsky equation,

E = E0 + RT/F ln (aH+ + KHNa * aNa

+)

Where, KHNa

= selective coefficient , for glasselectrode for Na ion in H+ ion.

Working range pH=1 to 12.

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1. Alkline error range (Non linear)2. Acidic error range

3. Linear range

Typical E vs pH diagram

http://en.wikipedia.org/wiki/File:PH_graph.jpg

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1. Sensing part , made by

specific glass.

2. Precipitates of Agcl.

3. 0.1M Hcl solution .4. Internal calomel electrode.

5. Glass body

6. Reference electrode

7. Junction with studied

solution.

Diagram for pH glass electrode

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Abbreviation: Pd/H2 Its characteristics similar to standard hydrogen

electrode (with platinum).

Potential of electrode is given by,

E = E0 + RT/F ln (aH+/(pH2)1/2)

Significant feature of paddalium is absorbmolecular hydrogen .

Other feature is absence of non stop bubbling ofmolecular hydrogen through solution.

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