elektrokimia anfar

7/29/2019 Elektrokimia Anfar

1/21


2/21

Oxidation: Loss of electrons or increase in the

oxidation number Fe 2+ + e- Fe3+

Reduction: Gain of electrons or decreases in theoxidation state

Cu2+ + 2 e- Cu

Redox reaction

Zn + Cu2+ - Zn2+ + Cu

Oxidizing agent: Species that is being reduced andcauses an oxidation

Reducing agent: Species that is being oxidized andcause a reduction


3/21

Ag(s)eAg

2eCuCu(s)2

2Cu2Ag(s)Cu(s)2Ag


4/21

eAgAg(s)

Cu(s)2eCu2

Cu(s)2AgCu2Ag(s)2


5/21

O3HNH8e10HNO

FeeFe

Ag(s)eAg

24-3

23

eFeFe

2e(g)Cl2Cl

2eCuCu(s)

32

2

-

2

- Oxidation takes place

-Reduction takes place


6/21

It is the driving force for either reduction or

oxidation half reaction, when by convention,

they are both written as reductions.

Cu2+ + 2e- Cu

Ag + + e- Ag


7/21

cathodeE

anodeE

AgM)(0.0200AgM)(0.0200CuCu

2Ag(s)Cu2AgCu(s)2

2

anodecathodecell

leftrightcell

EEE

EEE

AgM)(0.0200Ag

Ag(s)Ag

e

CuM)(0.0200Cu

Cu(s)2eCu

2

2

By convention, all Half-Cell reactions

are written as reduction half-reactions


8/21


9/21


10/21


11/21

Pt,)00.1(pHM)x]([HH

(g)He2(aq)2H

2

2

atm

sESHE

volt00.0


12/21

Ag1.00)(AgSHE

Ag1.00)(Ag1.00)(Hatm1.0HPt,

2Ag(s)H22Ag(g)H

2

2

a

aaVEEE

anodecathodecell 799.0


13/21


14/21

ba

dc

ba

dc

BA

DC

nEE

BA

DC

nF

RTEE

dDcCbBaA

][][

][][log

0592.0][][

][][ln

anodecathodecellEEE

anodecathodecellEEE

Remember -


15/21

One of the half-cells provides a known reference

potential, and the potential of the other half-cell

indicates the analyte's concentration. By convention, the reference electrode is taken to

be the anode; thus, the shorthand notation for apotentiometric electrochemical cell is

Reference IndicatorEcell= Eind- Eref+ Elj The ideal reference electrode must provide a stable

potential so that any change in Ecellis

attributed to the indicator electrode, and,therefore, to a change in the analyte'sconcentration.


16/21

Common reference electrodes

Standard Hydrogen Electrode (SHE) It is rarely used for routine analytical work, but is

important because it is the reference electrodeused to establish standard-state potentials for otherhalf-reactions.

A conventional salt bridge connects the SHE to theindicator half-cell.

The shorthand notation for the standard hydrogenelectrode is

Pt(s), H2 (g, 1 atm) H+ (aq, a = 1.00)

2H+(aq) + 2e H2(g); Eo = 0 V


17/21

Schematic diagram of the standard hydrogen electrode (SHE)


18/21

Schematic diagram of Ag/AgCl

reference electrode


19/21

Indicator Electrodes

The potential of the indicator electrode in a

potentiometric electrochemical cell is

proportional to the concentration of analyte.

Two classes of indicator electrodes are used

in potentiometry: metallic electrodes, and

membrane ion-selective electrodes.


20/21

Redox Electrodes

An inert electrode, Pt, that serves as a means

to supply electrons or as a sink for electronsinvolved in a redox half reaction

Pt | Fe3+ , Fe2+ ||

Fe3+ + e - Fe2+

Ecell = Eo - 0.059/n log([Fe3+]/[Fe2+])

What is the role ofPt in this electrode?

Q tit ti A l i i t l t d d


21/21

Quantitative Analysis using external standards

elektrokimia anfar

Documents