Basic science, important, Knowledge

1. BY
Dr. G.C.Wadhawa
DEPARTMENT OF CHEMISTRY
K. B. P. College,Vashi,Navimumbai
Electrogravemetry

2. Introduction
PrincipleAnd Instrumentation
Objective
Typesof electrogravimetric method
Mechanismof electrogravimetric
Application

3. Electrogravimetric analysis is more or less similar to conventional gravimetric analysis.
Howeverinelectrogravimetry theproductisdepositedquantitativelyonanelectrodebyan electrolytic
reaction and the amount of the product is determined by weighing the electrode before and after
electrolysis.The materialisdepositedonanelectrodebytheapplicationofa potentialinsteadofchemical
precipitation from a solution. Hence the name electrogravimetry (weighing of the product after
electrolysis).

4. Themainprinciple
involedinthismethodis
thedepositionof the
solidonanelectrod
fromtheanalyte
solution.

5. Explainthepricipleof elctrogravimetry
Explainohmicpotential(IRdrop)andpolarisationand theirsignificancein
electrodeposition.
Calculatethepotentialofagivencelltoinitiatedepositionofametalionof
calculatetheresidualconcentrationofioninsolutionbeforethe
commencementofthedepositionofnextion
Describeconstantcurrentandcontroledpotentialelectrogravimetry
Explaintheimportanceofcontrolledpotentialelectrogravimeteyinthesuccessive
depositionofmetalions

6. Therearetwotypesof electrogravimetric methods
(i) Constantcurrentelectrolysisand
(ii) Constantpotential electrolysis.

7. 1.Constant Current Electrolysis-
Herein electrodeposition is carried out by keeping the
current constant. Here periodic increases in the applied
potential are required (adjust the potential of the cell) as the
electrolysis proceeds.
the apparatus for constant current electrolysis consists of a
suitable cell and a direct current source. A 6 V storage
battery can be used for DC power source. An ammeter and
voltmeter are used to indicate the current and applied
voltage respectively. The voltage applied to the cell is
controlled by a resistor. The cathode is usually a cylindrical
platinum gauze.

8. Fig. Apparatus for constant current electrolysis

9. Constant Potential
Electrolysis-
 By controlled potential electrolysis,
it is possible to separate two elements
whose deposition potentials differ
sufficiently (by a few tenths of a volt).
 The potential of the cathode is
controlled so that it never becomes
sufficiently negative to allow the
deposition of the next element. As can
be seen from the the potential of the
cathode becomes negative (due to
concentration polarisation) and that co-
deposition of the other species begins

10. Fig.Apparatus for controlled-potential electrolysis. Contact C is adjusted as
necessary to maintain the working electrode (cathode in this example) at a
constant potential. The current in the reference-electrode circuit is essentially
zero at all times

27. 1.diffusion
2.migration
3.convection
Application-
1.quantitativeanalysis
2.Separation
3.Preconcentration
4.electrosynthesis