Lab Report

Title: Spectrophotometer and its function
Name: Ooi Shu Chien
Student ID: 00000014507

Objective: 1. To determine the wavelength of maximum absorption, Amax of bromophenol blue. 2. To construct a standard concentration curve for bromophenol blue. 3. To determine the concentration of the unknown bromophenol blue solutions. 4. To determine the concentration of two different solutes, bromophenol blue and methyl orange, in a mixture.

Material and method: Refer to practical manual page 7

Results:

Part 1: Determination of Amax of bromophemol blue

Table 1.1 Wavelength(nm) Absorbance 470 0.064 500 0.116 530 0.232 560 0.422 590 0.752 620 0.172 650 0.026 680 0.017

From graph 1, it can be seen that the highest peak is at wavelength 590nm, thus Amax of bromophenol blue is at wavelength 590nm. From table 1.1, it is shown that at wavelength 590nm, bromophenol blue has the Amax which is 0.752.

Part 2: The effect of concentration on absorbance of bromophenol blue solution

Table 1.2a Tube 1 2 3 4 5 6 A B
Distilled water(ml)
2.5
2.0 1.5 1.0 0.5 0

Bromophenol blue
10mg/L (ml)

0

0.5

1.0

1.5

2.0

2.5

Concentration of bromophenol blue(mg/L) 0

2.0

4.0

6.0

8.0

10.0

Absorbance at 590nm (Amax of bromophenol blue)

0

0.182

0.284

0.437

0.583

0.754

0.494

0.573
Absorbance at 460nm 0
0.030
0.041
0.048
0.050
0.055
0.012
0.016

According to Beer Lambert law,

Absorbance, A= λbc

λis the molar absorbtivity coefficient in L mg-1 cm-1 b is the path length(in cm) of the cuvette which the sample is contained c is the concentration of the compound in solution, in mol L-1

A = λbc is in the form of y = mx where m is the gradient of the straight line