Beer and Lambet law

Topics: 175, Chemistry, Spectroscopy Pages: 11 (377 words) Published: February 21, 2014
Tittle : Absorption Spectra and the Beer-Lambert Law. ɛ
Purpose : Understanding of Beer –Lambert Law
Introduction : When light passes through the colour solution , the molecules of the solution absorb the quantity of light at a particular wavelength . The amount of light which is absorbed by solution depend on two things. 1. The length of the pathway of light

2.Concentration of colour solution.
These are all explained by the Beer-Lambert Law.
Absorbance (A) = ɛcl
A= Absorbance
ɛ = molar absorption coefficient
(Depend on unit concentration )
c = concentration of colour solution.
l = length of the light path.
In here two experiments were carried out to clarify the relationship between concentration and absorbance in different wavelengths. According to the Beer-Lambert Law absorbance is directly proportional to the concentration of the colour solution or compound. Hypothesis : Able to determine the molarity of unknown solution through the Beer-Lambert law. Material : spectrometer,cuvettes, test tubes, water,Bromophenol blue(10mg/l),Methyle orange (10mg/l). Method : beginning of the experiment spectrometer was prepared for the experiments.It was confirmed that cuvettes were filled with a solution not more than than 2/3 full. Cuvettes were left in the compartment with clear side facing left and right. Experiment 1

Absorbance of Bromophenol Blue and Methyle Orange was measured in different wavelength between 400nm to 700 ,It was measured every 20 nm intervals. (Distilled water measurement was taken as zero.).λmax was identified for the two dyes.further reading was made to get pricise λ max in higher absobance. Table 1

BromoPhenol Blue.
Absorbance

Further reading to determine '
λ max'

Wavelength (nm)

Wavelength (nm)

Absorbance
400

0.101

590

0.874

420

0.047

592

0.938

440

0.038

608

0.869

460

0.049

610

0.811

480

0.067

500

0.098

520

0.165

540

0.28

560

0.444

580

0.673

600

0.983

620

0.444

640

0.081

660

0.011

680

0.003

700

0

Experiment 2
Ten different concentrated dilute solutions were prepared for Brromophenal Blue and Methyle Orange.absorbance was measured against every different concentration of solution. Table Number
Briomopenol Blue

Methyle Orange

Absorbance 'λmax'

Absorbance 'λmax'
1

0.091

0.067

2

0.196

0.143

3

0.304

0.217

4

0.401

0.287

5

0.489

0.345

6

0.588

0.43

7

0.679

0.51

8

0.775

0.58

9

0.881

0.647

10

0.971

0.719

Table no

1
2
3
4
5
6
7
8
9
10
Stock solution
0.3
0.6
0.9
1.2
1.5
1.8
2.1
2.4
2.7
3
(10mg/l)
(ml)

Distilled water(ml)
2.7
2.4
2.1
1.8
1.5
1.2
0.9
0.6
0.3
0
Concentration
1
2
3
4
5
6
7
8
9
10
(mg/l)

c oncentration%
0.33
0.66
1
1.33
1.66
2
2.33
2.66
3
3.33

Methyle Orange(nm) absorbance
range

further reading to determine
λ max'
Wawelength
th (nm)
Absorbance

wavelelength(nm) absorbance
400

0.356

450

0.667

420

0.487

452

0.675

440

0.609

468

0.726

460

0.714

470

0.727

480

0.695

500

0.56

520

0.352

540

0.146

560

0.04

580

0.008

600

0.002

620

0.001

640

0.001

660

0.001

680

0.001

700

0

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