Azo – dye Test

Equipment and chemicals

organic compound

sodium nitrate

β-naphthol

distilled water

dilute HCl

dilute NaOH

ice cold water

test tubes

droppers

Procedure

1.Take small quantity of organic compound, sodium nitrate and B-naphthol in test tubes A,B,C.

  1. Using a dropper add a small quantity of dilute HCl to test tube A.
  1. Shake the test tube well to dissolve the compound in HCl.
  1. Add a small quantity of distilled water to test tube B.
  1. Shake the test tube well to dissolve sodium nitrate in distilled water.
  1. Add a small quantity of dilute NaOH to test tube C.
  1. Shake the test tube well to dissolve β-naphthol in dilute NaOH solution.
  1. Cool the test tubes in a beaker containing ice cold water for some time.
  1. Add sodium nitrate solution to the organic compound.
  1. Add the resulting solution to test tube C.

Observations

The organic compound is a clear, orange liquid. Dilute hydrochloric acid is a colorless, clear liquid. When we placed a few drops of hydrochloric acid in test tube A containing organic compound, bubbles appeared and the mixture turned blurry. In test tube B we placed sodium nitrate, which is a white, solid matter. Distilled water is a colorless, clear liquid. When distilled water is put in the test tube, sodium nitrate dissolves, creating a clear mixture. β-naphtol in test tube C is a light red/pink solid. Sodium hydroxide is a clear, colorless liquid. When it is placed in test tube C, β-naphthol dissolves creating a blurry, light brown solution. When the mixture from test tube B was added to test tube A, the solution turned yellow/orange, bubbles appeared. The resulting solution was added to test tube C, the mixture turned dark red.

Sketch of experiment

Conclusion

Primary amine, on reaction with nitrous acid formed from sodium nitrite and hydrochloric acid, gives diazonium salt. The diazonium salt undergoes coupling reaction with beta-naphthol to form a scarlet red coloured compound called azo dye.

Chemical equation