SPECTROPHOTOMETRIC ESTIMATION OF BROMIDE

Abstract:

Bromide ion is determined in spectrophotometer by using chloramine T as an oxidizing agent,Phenol Red and Methyl Red as colourimetric reagent,colour of which decrease with increasing bromide ion concentration.

Principle:       

Bromide in a chloride solution can be oxidized preferentially to elemental bromine which will dcolourize common indicators like phenol Red and Methyl Red, in the process decreasing the O.D of the indicators at their λ_max. Oxidizing agent used was Chloramine T.Two indicators were used-Phenol Red and Methyl Red. With increasing Bromide concentration, more decrease in O.D was observed in both the indicators.

Spectrophotometer Used:   

Varian Carry 50

Reagents Used:

1. 0.01% Chloramine T solution

2. 0.01% phenol red solution

3. 01% methyl red solution

4. Standard Bromide solution of strengths: 2 ppm, 4 ppm, 6 ppm, 8 ppm — made  from GR grade K Br.

Study of maximum absorption of light

Procedure: 

1. To 50 ml each of standard solutions of bromide of concentration 2 ppm, 4 ppm, 6 ppm, & 8 ppm. 0.5 ml 0.01% Chloramine T & 0.5 ml 0.01% Phenol Red were added. language conversion . pH was maintained at 5.0 & absorbance was measured at 430 nm. Standard graph was plotted. Now 5 ppm standard solution was measured using the same procedure.
2. The same procedure was carried out as in (a). 0.5 ml 0.01% Methyl Red was added instead of Phenol Red and absorbance was measured at 520 nm. 

Preparation of calibration graph

1. Phenol Red

2. Methyl Red

Calibration graph of Standard Bromide solution using Phenol Red as a colourimetric reagent at lamda max 430nm

Graph attached for standard bromide solution using Phenol Red as a colourimetric reagent

Calibration graph of Standard Bromide solution using Methyl Red as a colourimetric reagent at lamda max 520nm

Graph attached for standard bromide solution using Methyl Red as a colourimetric reagent

Graph attached for unknown bromide solution using Phenol Red as a colourimetric reagent

Graph attached for unknown bromide solution using Methyl Red as a colourimetric reagent

Conclusion:

Both the indicators can be used at a pH 5 and the decreasing optical density with increasing Bromide concentration will be measured of Bromide ion present in the solution. Both the methods are more or less equally accurate and can be used for daily estimation of Bromide in chloride admixture.

Contributed by:  Ms. Alakta Saha under the guidance of Prof.Barun Gupta