Question

What is the Silver nitrate used for?

Answer 1

Silver nitrate (${\mathrm{AgNO}}_3$) is used for the identification of two different forms.

Part 1: Halogen identification test

• A small piece of Sodium metal is heated in the fusion tube with an organic compound and Sodium converts all the metal into ionic form$\underset{\mathrm{Sodium}}{\mathrm{Na}\left(\mathrm{s}\right)}+\underset{\mathrm{Halogen}}{\mathrm{X}\left(\mathrm{s}\right)}\to \underset{\mathrm{Sodium}\mathrm{halides}}{\mathrm{NaX}\left(\mathrm{s}\right)}$
• The reaction between the Silver nitrate and Sodium halides forms Silver halides and Sodium nitrate then obtained different colour precipitates that depend on the presence of halide.
  $\underset{\mathrm{Silver}\mathrm{nitrate}}{{\mathrm{AgNO}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Sodium}\mathrm{halide}}{\mathrm{NaX}\left(\mathrm{s}\right)}\to \underset{\mathrm{Silver}\mathrm{halide}}{\mathrm{AgX}\left(\mathrm{s}\right)}+\underset{\mathrm{Sodium}\mathrm{nitrate}}{{\mathrm{NaNO}}_3\left(\mathrm{aq}\right)}$

Type of halide	Colour
Silver chloride	White
Silver bromide	Pale cream
Silver iodide	Pale yellow

Part 3: Tollen's Test

• Tollen's reagent is a solution of Silver nitrate and ammonia.
• Tollen's test is used to distinguish between aldehydes and ketones.
• Only aldehyde shows a positive Tollen's reagent test.
• It is also known as the Silver mirror test because a white precipitate of silver is formed on the inner side of the test tube.
• The white precipitate is due to the reduction of Silver salt to Silver metal and the oxidation of an aldehyde to Carboxylic acid.
• The reaction for the oxidation of aldehydes to Carboxylic acid by the Tollen's reagents is shown below: $\underset{\mathrm{Ethanal}}{{\mathrm{CH}}_3\mathrm{CHO}\left(\mathrm{l}\right)}+\underset{\mathrm{Silver}\mathrm{ion}}{2{\mathrm{Ag}}^{+}\left(\mathrm{aq}\right)}+\underset{\mathrm{Hydroxide}\mathrm{ion}}{2{\mathrm{OH}}^{-}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Ethanoic}\mathrm{acid}}{{\mathrm{CH}}_3\mathrm{COOH}\left(\mathrm{l}\right)}+\underset{\mathrm{Silver}}{2\mathrm{Ag}\left(\mathrm{s}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$