Spectrophotometer and Its Function

Part 1: Determination of Amax of bromophenol blue

RESULTS:

Table 1.1

Wavelength (nm)

Absorbance

470

0.178

500

0.249

530

0.439

560

0.690

590

1.313

620

0.323

650

0.075

680

0.060

Graph 1.1

Graph of absorbance spectrum (absorbance readings versus corresponding wavelength)

DISCUSSION:

According to Graph 1.1, the wavelength with maximum absorbance is 590nm with the absorbance of 1.313, as it is the highest point of the bell-shaped graph. Therefore the Amax of bromophenol blue is 590nm.

CONCLUSION:

Amax of bromophenol blue is 590nm.

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

Results:

Calculation of the concentration of bromophenol blue after dilution with distilled water:

Formula:

M1V1=M2V2

where,

M1= concentration of bromophenol blue used for dilution (10mg/L)

V1= volume of bromophenol blue used

M2=concentration of bromophenol blue after dilution

V2= total volume of diluted solution (2.5ml)

TUBE 1

M1V1=M2V2

10(0)=M2(2.5)

M2= 0 mg/L

TUBE 2

M1V1=M2V2

10(0.5)=M2(2.5)

M2= 2mg/L

TUBE 3

M1V1=M2V2

10(1)=M2(2.5)

M2=4mg/L

TUBE 4

M1V1=M2V2

10(1.5)=M2(2.5)

M2=6mg/L

TUBE 5

M1V1=M2V2

10(2)=M2(2.5)

M2=8mg/L

TUBE 6

M1V1=M2V2

10(2.5)=M2(2.5)

M2=10mg/L

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 10 mg/L (ml)

0

0.5

1.0

1.5

2.0

2.5

-

-

Concentration of bromophenol blue (mg/L)

0

2

4

6

8

10

-

-

Absorbance at 590 nm (Amax of bromophenol blue)

0

0.188

0.558

0.574

0.599

0.963

0.513

0.267

Absorbance at 460 nm

0

0.019

0.033

0.055

0.077

0.087

0.028

0.019

The results on Table 1.2a are used to plot the standard concentratioon curve of absorbamce versus concentration of bromophenol blue as shown in Graph...