Electrogravimetry involves the electrolytic deposition of an element onto an electrode, which is then weighed before and after deposition to determine the amount deposited. There are two main methods - constant current electrolysis, where current is kept constant and potential varies, and constant potential electrolysis, where potential is kept constant. Electrogravimetry can be used to determine the concentration of elements in solutions and to separate elements electrolytically based on their deposition potentials. It has applications in quantitative analysis, electrosynthesis, separating species in solutions, and purifying reagents.

1. ELECTROGRAVIMETRY
PRESENTED BY
JAYANTH .J .KONAREDDI
Dept of chemistry

2. contents
 INTRODUCTION
 THEORY
 APPARUTUS
 ELECTROLYTIC SEPARATION
 APPLICATION

3. INTRODUCTION
 In Electrogravimetric analysis , the element to be determined is deposited
electrolytically upon a suitable electrode and the amount of product is
determined by weighing the dry electrode before and after exhaustive
analysis.
 The co-deposition of two metals can often be avoided under the carefully
controlled experimental condition.
 It has numerous advantages.

4. THEORY
 Electrodeposition is governed by OHM’s law and FARADAY’s law of electrolysis.
 Ohm’s law : The current (I) is directly proportional to electromotive force E and inversely
proportional to the resistance R.
 Faraday’s law : The amount of substance liberated (or dissolved) at the electrode of a cell
are directly proportional to quantity of electricity which passes through the solution.
W C×t = Z C×t
where W = wt. of of the substance deposited, C = current in amperes, t = time
in sec
Z = constant of proportionality, called electrochemical eq.
When C = 1 amp; t = 1s, then W = Z.

5. Types of electrogravimetry methods
• THERE ARE TWO TYPES OF ELECTROGRAVIMETRY
METHODS
1. CONSTANT CURRENT ELECTROLYSIS
2. CONSTANT POTENTIAL ELECTROLYSIS

6. 1.Costant current electrolysis
 Herein electrodeposition carried out by keeping constant
current.Here periodic increase in the applied potential are
required as the electrolysis proceeds.
 Apparatus:
It consists of suitable cell, direct current
source and two electrodes
 Cells: Two cells are dip in container electrode connected to
circuit
 Cathode: Working electrode is a large surface area use
platinum gauze cylinder (-ve electrode)
 Anode: It is a solid rod with attached to electrical rotating
motor connected to cathode to external circuit (+ve
electrode)
 6-12V storage battery used for DC power supply
 An ammeter and voltmeter used to indicate current and
applied voltage respectively

7. 2. Constant potential electrolysis
 It is possible to separate two elements whose deposition potentials
differ sufficiently(by a few tenths of a volt)
 It is made up of independent electrical circuits that shares a common
electrode
 Working electrode where analyte is deposited
 The electrolysis circuit consists of a DC source, a potentiometer that
permits the voltage applied between the working electrode and
counter electrode to be continuously varied and a current meter
 The control circuit made up of a reference electrode(SCE),a high
digital meter and working electrode
 Control circuit continuously monitors the voltage between working
electrode and reference electrode and maintains it at a controlled
value

8. Electrolytic separation
Determination of copper:
 Principle: Copper may be deposited from either HNO3 or H2SO4 but
usually mixture of 2 acids is implied, if such solution is electrolyzed
with an EMF of 2-3V then the following reactions
Reactions: cathode cu
2+
+ 2e- cu ; 2H
+
+ 2e- H2
anode 4OH- O2 + 2H2O + 4e-
The acid concentration must not to be great,otherwise deposition will not
adhere to the cathode. Nitrite ions acts as a depolarizer at the cathode.
NO3 + 10H
+
+8e- NH4
+
+ 3H2O
The reduction potential of NO3 ions is lower than discharge potential of
hydrogen,so H2 is not liberated. HNO3 must be free from HNO2 bcoz the
NO2 ions hinder the complete deposition,so the HNO2 may be removed
boiling of HNO3

9. Procedure:
 Dissolve 1g of CuSo4 or 0.25g of Cu in 1:1 HNO3 boil to remove HNO2 fumes, just neutralize with the ammonia
 Acidified with dil.H2SO4 and dilute to 100cm3. The solution(HNO3 100cm3) may contain 0.2-0.3g Cu
 Add 2cm conc.H2SO4, 1cm conc HNO3 and transfer to electrolytic vessel
 Clean, dry and weigh platinum guaze electrode
 Assemble the apparatus with magnetic stirrer,cover the beaker, switch on the stirrer and adjust potential difference 3-
4V and current to 2-4A
 Continue the electrolysis until blue colour disappears
 Reduce the current to 0.5-1A, test the completeness of deposition by rinsing the split clock glass
 Rising the level of liquid by adding 0.5cm of distilled water. Electrolytsis continue for the next 20 minutes
 If no copper is deposited on fresh surface of cathode,electrolysis is complete
 Lower the vessel and rise the electrodes, wash the cathode. Break the circuit, dip the cathode into beaker of distilled
water and rinse it with acetone
 Dry at 373-383Kfor 3minutes and weigh after cooling
 Calculate the copper content of solution after the cathode has been weighed, it shold be cleaned with HNO3 and
reweighed. The loss in weight will serve as a check.

10. Determination of some other elements
IONS Weighed on Electrolyte Conditions
Co2+ Co Ammonical sulphate solution 4A; 3-4V
Ni2+ Ni Ammonical solution 4A; 3-4V
Zn2+ Zn KOH solution 4A; 3.5-4.5V
Cd2+ Cd KCN forming K2[Cd(CN)4] 1.5-2A; 2.5-3V

11. Applications of ELECTROGRAVIMETYRY
 Electrogravimetry used for determination of concentration of chemical elements very accurate
and precisely in quantitative analysis
 In organic electrosynthesis it is used by organic chemist for conducting oxidation and reduction
 In solution of different species are separated by selectively plating out and removing out.It is
used in electrochemical methods for removing interference
 It is used in purification – removal of trace metals from reagents by plating them onto large Hg
pool electrode
NOTE:
*electrosynthesis: synthesis of chemical compounds in a electrochemical cell

12. Jayanth
Konareddi