E-MODULE SKA3013 (ELECTROCHEMICAL METHODS)

E-MODULE

ELECTROCHEMICAL
METHODS:

ANALYTICAL CHEMISTRY
SKA3013

GROUP C (A211)

LECTURER :DR. SITI NUR AKMAR BINTI MOHD YAZID

GROUP MEMBERS

TABLE OF CONTENTS

01 02 03
INTRODUCTION APPLICATIONS
PROBLEM
SOLVING

04 05 06
EXERCISES CONCLUSION REFERENCE

01.

INTRODUCTION

ELECTROCHEMICAL METHODS

Electrochemistry Electrochemical methods

-a branch of chemistry concern with the -that use a measurement of potential, charge, or
interaction of electrical and chemical effects current

-the study of chemical change by passage of -to determine an analyte's concentration
an electrical current and production of or to characterize an analyte's chemical
electrical energy by chemical reaction reactivity

-involving the movement of electron in redox -a qualitative & quantitative methods based
reaction on electrochemical phenomena occurring within
a medium or at the phase boundary which are
Type of related to the changes in the:
electrochemical methods
a) structure
a) potentiometry b) chemical composition
b) voltammetry c) concentration of the compound
c) coulometry
d) conductometry

A) Potentiometry method

When the known potential electrode

Based on the potential measurement of T is immersed in the sample solution then the
electrochemical cells without any potential is given by Nernst equation:
appreciable current. H

E E= E0 +(0.592/n) log c

O E: the potential of the solution

R E0 : the standard electrode potential
n: the valency of the ions
Y c: the concentration of the sample solution

Components of a Potentiometric Cell:
1. Reference electrode
2. Salt bridge
3. Analyte
4. Indicator electrode

B) Voltammetry method

Based on the applies a constant or Polarographic Analysis - the measurement of
varying potential at an electrode's surface. current electrolysis of an electroactive species at
a given electrode potential under controlled
conditions.

Used for the determination of compounds
in solutions for example in polarography.

C) Coulometry method D) Conductometry method

The measurement of the amount The measurement
of material deposited on an electrode of the electrical conductivity (aqueous and
in electrochemical reaction in accordance non-aqueous solutions, colloid system and
with Faraday's Laws. solids).

Faraday's laws - the amount of
substance produced at each electrode is
directly proportional to the quantity of
charge flowing through the cell.

02.

APPLICATION

ELECTROCHEMICAL METHOD

1 Obtaining To generate an 3
thermodynamic data unstable
about a reaction
intermediate such as
radical ion

2 To analyze a solution The electrochemical 4
for trace amount of properties of
metal ions or organic
species themselves are of
primary interest, for
example in the design
of a new power source

03.

PROBLEM
SOLVING

ELECTROCHEMICAL METHODS

Q.1

What mass of aluminium can be produced in 8.00 min by passing a
constant current of 100 A through a molten mixture of aluminium
oxide, Al2O3?

Aluminium is formed from: Al3+ + 3e- Al (s)

100 A = 100 C
1s

8.00 min x 60 s x 100 C x 1 mol e- x 1 mol Al x 26.98 g Al
1 min 1 s 96 500 C 3 mol e 1 mol Al

= 4.47 g of Aluminium will be produced

Q.2

What current would be needed to deposit 5.0 g of zinc from a
solution of ZnCl2 in 1.0 h?

Copper is formed from: Zn2+ + 2e- Zn (s)

5.0 g Zn x 1 mol Zn x 2 mol e- x 96 500 C x 1 x 1 h
65.39 g 1 mol Zn 1 mol e- 1.0 h 3600s

= 4.1 A current is needed

Q.3

For each of the following cells, write a balanced equation for the half-cell reaction at

each electrode and calculate the cell potential. Indicate whether the redox reaction in

the cell is spontaneous under the given conditions
a) Fe (s) | FeBr2 (0.010 M) || NaBr (0.050 M) | Br2 (l) | Pt (s)

b) Pt (s) | Hg2Cl2 (s) | Hg (l) | KCl (0.060 M) || Cu (NO3)2 (0.020 M) | Cu (s)

a) Fe(s) ⇌ Fe2+(aq)+ 2e- E0 ox = 0.44 V

anode:

cathode: Br2(l) + 2e- ⇌ 2Br-(aq) E0 red = 1.078 V

0.499

Ecell = Eox + Ered = 0.499 V + 1.155 V = 1.65 V

.

Since Ecell is > 0, the cell redox reaction is spontaneous.

b)

-0.3403

0.2887

anode: 2Hg(l) + 2Cl-(aq) ⇌ Hg2Cl2(s) +2e- E0ox= 0.268

V cathode: Cu2+(a. q) + 2e- ⇌ Cu(aq) E0 = 0.339 V
red

Ecell = Eox + Ered = -0.3403 V + 0.2887 V = -0.052 V

Since Ecell is < 0, the cell redox reaction is nonspontaneous

Q.4

a) E0 Hg2Cl2/Hg (calomel electrode) = 0.268 V. How would you expect the potential
for a KCl-saturated calomel electrode to compare? Explain.

b) Calculate the activity of Cl- in a KCl- saturated calomel electrode.

a) For the calomel electrode, Hg2Cl2(s) + 2e- ⇌ 2Hg(l) + 2Cl (aq) and E0red = 0.268 V.

Increasing the [Cl-] by saturating the solution with KCl should “push” the reaction in
favor of the reactants (Le Chatelier) and thus decrease the half-cell potential.
EHg2Cl2/Hg (KCl-sat’d calomel electrode) = 0.241 V.

b)

0.241 V = 0.268 V - 0.05915 log aCl-
aCl- = 2.86

Q.5

Is the redox reaction occurring in the following cell spontaneous under standard
conditions? Explain.

Pb(s) | PbSO4(s) | K2SO4(aq) || H2SO4(aq) | PbSO4(s) | PbO2(s) | Pb(s)

anode: Pb(s) + SO42-(aq) ⇌ PbSO4(s) + 2e- E0ox = 0.355V

cathode: PbO2(s) + 4H+(aq) + SO42-(aq) + 2e- ⇌ PbSO4(s) + 2H2O(l)

E0red = 1.685 V
E0cell = E0ox + E0red = 0.355 V + 1.685 V = 2.040 V
Since Ecell is > 0, the cell redox reaction is spontaneous.

Q.6

Which of the following will be the strongest oxidizing agent under
standard conditions? Explain your choice.

HNO2 Se UO2 2+ Cl2 H2SO3 MnO2

The strongest oxidizing agent Reaction E0red (V)
under standard conditions will
have the most positive value of E0red. HNO2/NO 0.984
Se/H2Se -0.082
Z Cl2 is the strongest oxidizing agent UO22+/U4+ 0.273
Cl2/Cl- 1.360
H2SO3/S2O32- 0.40
MnO2/Mn2+
1.23

04.

EXERCISES

ELECTROCHEMICAL METHODS

~ Practice Makes Perfect ~

a) For the following cell, write a balanced equation for each half-reaction
occurring at the electrodes and the Nernst equation for the overall cell
reaction.
Pt(s) | H2(g, 1.00 bar) | H+(aq, pH = 3.60) Cl-(aq, ?M) | AgCl(s) | Ag(s)

b) If the cell potential is 0.485 V, what is the [Cl-] in the cathode solution?

Pb2+(aq) and Ag+(aq) were produced when a 0.978 g sample of
nitric acid was dissolved. After diluting the solution to 250.0 mL of
deionized water, a silver electrode was placed in the solution. The
potential difference read 0.273 V. Calculate the mass of Ag in the
sample as a percent.

Find Ecell for the following cells y using the Nernst equation
a. Na(s) |Na+ (0.32 M) ||Mg2+ (0.025 M)| Mg(s)

E0(Mg2+ /Mg) = -2.356 V
E0(Na + /Na) = -2.713 V

b. F- (0.03 M) | F2 (1.02 bar) || Cu2+ (0.2 M) |Cu(s)
E0(Cu2+ /Cu) = 0.340 V
E0(F2/F-) = 2.866 V

Determine the anode and cathode of the following reactions. Then,
calculate the reaction’s equilibrium constant, K.
a. Ca2+ (aq) + 2Li(s) → Ca(s) + 2Li+(aq)

E0(Ca2+ /Ca)= -2.84 V
E0(Li+/Li)= -3.04 V

b. H2SO3(aq) + 4H+(aq) + 4[Fe(CN)6]4− (aq) → S(s) + 3H2O(l) +
4[Fe(CN)6]3−

E0(H2SO3/S) = 0.449 V
E0(Fe (CN)64−/ Fe (CN)63-) = 0.361 V

Calculate the dissociation constant KHP for the weak acid HP if
the cell develops:

SCE || HP (0.010 M),NAP (0.040 M) | Pt,H2 (1.00 atm)
(a potential of – 0.591 V)

A voltaic cell has an Ecell value of 1.536 V. What is the concentration
of Ag+ in the cell?

Zn(s) |Zn2+ (2.00 M) || (Ag+ (x M) |Ag(s)

E0(Zn2+/Zn) = -0.763 V
E0(Ag+/ Ag) = 0.800 V

[ANSWER SCHEME]

05.

CONCLUSION

ELECTROCHEMICAL METHODS

Electrochemical methods are the proper application of such techniques
requires a strong connection between electrochemistry fundamentals and
engineering science. All electrochemical methods are based on the
interaction of electrical energy and matter. From this learning, the
students know that measurements are done in an electrochemical
cell where the sample and at least two electrodes are placed. The
electrochemical cell possesses a large variety of concentration-
dependent physical characteristics that may be exploited for chemical
analysis. The methods are mainly used in analysis of aqueous samples but
are also applicable to nonaqueous solutions and gases. In most of the
methods one concentration-dependent electrical parameter, like voltage,
current, resistance, or charge, is measured while the others are kept
constant or manipulated to receive the desired response that correlates to
the sample composition.

REFERENCES

1. Chemistry LibreTexts. 2022. 11.S: Electrochemical Methods (Summary). [online] Retrieved from
https://chem.libretexts.org/Courses/Northeastern_University/11%3A_Electrochemical_Methods/11
.S%3A_Electrochemical_Methods_(Summary).

2. Chem 321 Lecture Postings. Retrieve from: http://www.csun.edu/~hcchm003/321/321postold6.html.

3. Slideshare.net.2022. Electrochemical method of analysis. [online] Retrieved from
https://www.slideshare.net/SihamAbdallaha/electrochemical-method-of-analysis-31352857.

4. 4.9: Exercises on chemical kinetics. (2021, May 9). Retrieved from
https://chem.libretexts.org/Courses/Mount_Royal_University/Chem_1202/Unit_4%3A_Chemical
_Kinetics/4.9%3A_Exercises_on_Chemical_Kinetics.

THANK
YOU