How can chemists test a sample for bromine?

Chemists use several qualitative and quantitative methods to test for the presence of bromine in a sample.

Qualitative Tests

• Colorimetric Reactions: A sensitive test involves reacting the sample with fluorescein, which produces a deep red color due to bromination. Alternatively, reaction with fuchsine dyes in the presence of sulfurous acid yields a deep blue color.1
• Oxidation and Extraction: Heating a sample with dilute sulfuric acid and potassium dichromate releases bromine, which can be extracted with chloroform. Adding potassium iodide to this extract produces the characteristic pink color of iodine.1
• Direct Observation: Treating a solid sample with concentrated sulfuric acid may evolve hydrogen bromide along with brown bromine vapor. Additionally, adding chlorine to an aqueous solution containing bromide causes the development of a brown color, indicating free bromine.1

Quantitative Determination

• Titration: Free bromine can be titrated with sodium thiosulfate in the presence of potassium iodide.1
• Gravimetric Analysis: Bromides can be determined by weight analysis or by titration with silver nitrate.1
• Complex Samples: In the presence of other halides, potentiometric methods are used. For organic compounds, the sample is typically oxidized with nitric acid and the bromine is measured as silver bromide.1