Name; Hasnain Nawaz Surname : Shaikh ROLL NO: 16 CH 42 B.E: Chemical Engineering (In Progress). Mehran University of Engineering and Technology Jamshore, ISO 9001 Certified.

1. Topic:-
Ultra Violet / Visible Spectroscopy
ROLL NO# 16 CH 42
PHYSICAL & ANALYTICAL CHEMISTRY

2. Contents
 Introduction to Spectroscopy
 Electromagnetic Radiations
 Principle Of Ultra Violet and Visible Spectroscopy.
 Interaction of Electromagnetic Radiations with Matter.
 Lambert’s Law and Beer’s Law
 Applications Of Ultra violate and Visible Spectroscopy.

3. Spectroscopy
 It is the branch of science that deals with the
study of interaction of Matter with Light.
OR
 It is the branch of science that deals with the
study of interaction of Electromagnetic Radiation
with Matter.

4. Spectroscopy
 SPECTROSCOPY is the measurement and
interpretation of Electro Magnetic Radiation (EMR),
absorbed or emitted when the atoms, molecules or
ions of a sample move from one energy state to
another energy state.

5. Electromagnetic
Radiationadiation

6. Electromagnetic Radiation
 Electromagnetic radiations consist of discrete
packages of energy which are called as Photons.
 A photon consists of an oscillating electric field (E) &
an oscillating magnetic field (M) which are
Perpendicular to each other.

8. Principles of
Spectroscopy

9. PRINCIPLE OF UV- VISIBLE SPECTROSCOPY
 VISIBLE SPECTROSCOPY
Visible Spectroscopy is concerned with the study of
Absorption of visible radiation whose wavelength ranges
from “400nm-800nm”.
Any Coloured substance will absorb radiation in this
wavelength region.

10.  Ultra Violet SPECTROSCOPY
 Ultraviolet spectroscopy is concerned with the study of
absorption of UV radiation which ranges from “200 to
400nm”.
 Compounds which are coloured, absorb radiation from
400-800nm (visible spectroscopy). But compounds which
are colourless absorb radiation in the UV region.

11.  In both Ultra Violet as well as Visible spectroscopy only
the valence electrons absorb the energy.
 So the atoms undergo transition from Ground state to
Excited state.
 Thus absorption is a characteristic which depends on the
Nature of electrons present.
 And The intensity of absorption depends on the
concentration.

12. Interaction of
EMR with Matter
with
Matter

13. Interaction of EMR with matter
1. Electronic Energy Levels:
 At room temperature the molecules are in the
lowest energy levels E0.
 When the molecules absorb UV-visible light from
EMR, one of the outermost lone pair electron is
promoted to higher energy state such as E1, E2,
…En, etc is called as Electronic transition and the
difference is as:
∆E = h ν = En - E0 where (n = 1, 2, 3, … etc)

14. 2. Vibrational Energy Levels:
 These are less energy level than electronic energy
levels.
 The spacing between energy levels are relatively
small i.e. 0.01 to 10 kcal/mole.
 E.g. when EMR radiation is absorbed, molecules
excited from one vibrational level to another or it
vibrates with higher amplitude.

15. 3. Rotational Energy Levels:
 These energy levels are quantized & discrete.
 The spacing between energy levels are even
smaller than vibrational energy levels.
∆Erotational < ∆Evibrational < ∆Eelectronic

16. LAWS GOVERNING
U-V / Visible
Spectroscopy

17. Lambert’s Law

18. Lambert’s Law
 The law states that,
When a Monochromatic Radiation is passed through a
solution, the decrease in the intensity of Radiation and
thickness of the solution is directly proportional to the
intensity of the incident light.
Let “I” be the intensity of Incident light and “X” be
thickness of Solution, then,

19. Mathematically we can write,
I
dx
dI

So, KI
dx
dI

Integrate equation between limit
I = I at x=l,
I = Io at x = 0 and
We get,
Kl
I
I

0
ln

20. Lambert’s Law
Kl
I
I

0
log303.2
l
K
I
I
303.2
log
0

Where, AbsorbanceA
I
I
0
log
E
K

303.2
lEA .
Absorption coefficient
Lambert’s Law

21. Beer’s Law

22. Beer’s Law
 When a Monochromatic Radiation is passed through a
solution, the decrease in the Intensity of Radiation with
Thickness of the Solution is directly proportional to the
Intensity of the Incident light as well as Concentration
of the solution.
Let “I” be the intensity of Incident light ,
“X” be thickness of Solution, and
“C” be the Concentration of the Solution.
Then

23. Mathematically we can write,
IC
dx
dI
.
So, ICK
dx
dI
.'
Integrate equation between limit
I = Io at x = 0 and
I = I at x=l,
We get,
lCK
I
I
.'ln
0


24. Beer’s Law
lCK
I
I
..log303.2 0

lC
K
I
I
.
303.2
log 0

Where, AbsorbanceA
I
I
0
log
E
K

303.2
lCEA ..
Molar extinction
coefficient
Beer’s Law

25. Applications of
UV / Visible
Spectroscopy

26. Applications
 Qualitative & Quantitative Analysis:
1. It is used for characterizing aromatic compounds and
conjugated olefins.
2. It can be used to find out molar concentration of the solute
under study.
 Detection of Impurities:
 It is one of the important method to detect impurities in organic
solvents.
 Detection of isomers are possible.
 Determination of molecular weight can be done using Beer’s law.