Principles of Electrolysis in Aqueous Solution

Nurhasanudin3334081633

1

19 April 2011

Outline

1. Preface2. Electrochemistry of Aqueous Solution3. The Possibilities of Reaction in Anode and Cathode4. Predicting The Product of Electrolysis in Aqueous

Solution5. Hydrogen Evolution During Electrolysis in Aqueous

Solution6. Anodic and Cathodic Reaction During Electrowinning

and Electrorefining in Aqueous Solution7. Refference

2

Preface

3

Electrolysis

Aqueous Solution

Fused Salt

Type of Aqueous Solition Electrolyte

Acid Basic Salt

4

Example NaCl

Fused salt

When heat NaCl till it melts temperatur, then we will get molten Nacl, is called fused salt of sodium chloride

NaCl Na+ + Cl-

Aqueous solution

Whereas if NaCl is dissolved in water, gives the aqueous solution of sodium chloride

NaCl Na+ + Cl-

H2O H+ + OH-

5

Electrochemistry of Aqueous Solution

The total electromotive force of a cell may be regarded as consisting of a cathodid and an anodic potential. Thus for a cell :

X/X-, A+/A

The two half cell corespond to the reaction :

A+ + e- = A and X- = X + e-

The first of these may be called reduction the second an oxidation

The total emf as different between two reduction potential

E = E A+/A - EX/X-

6

The half cell potential may again be expressed in term of standard half-cell potential in the electrolyte

7

Possibilities of reaction in anode and cathodeAnode

4OH- 2H2O + O2 + 4e-

 

X- X + e-

here there is choice of hydroxide or other negative ion will be discharge

to anode

Cathode

2H+ + 2e- H2

A+ + e- A

here each two hydrogen ion can gains two electron and become

hydrogen atom, also occur to the other positif ion but only one will be

selected

8

Predicting The Product of Electrolysis in Aqueous Solution

There is three factor to be discharged

1. Reactivity series 2. Concentration of solution3. The kind of electrode used

9

Hydrogen Evolution During Electrolysis of Aqueous Solution

Hydrogen ions are always present in aqueous electrolyte And lowering the current efficiency at the cathode

10

The following need to know about hydrogen evolution

1. The equilibrium single electrode potential of the metal and hydrogen

2. The η-i relationship for the discharge of metal as well as hydrogen at the cathode

11

The Polarisation curve

12

Tabel of Reduction Potentials

13

Anodic and Chatodic Reaction During Electrowinning And Electrorefining in Aqueous Solution

In aqueous solution electrolysis the anode is generally made of an inert lead based alloy (usually Pb, Sb, As). The anodic reaction in acidic and alkaline aqueous solution may be written as follows.

Acidic solution 2H2O = O2 + 4H+ + e- , Eo = - 1,23

Alkaline solution 4OH- =2H2O + O2 + 4e-, Eo =-0,40V

14

REFFERENCE

Rosenqvist. Principles of Extractive Metallury, McGraw Hill Kogakusha Ltd., Tokyo, 2nd ed., 1983.

Ray&Ghosh. Principles of Extractive Metallury,

2nd ed.1991 http://myadvocator.com/chemistry/quick-revision-series/electrolysis-of-aqueous-

solution/

15

16