Silver nitrate or Lunar caustic: Preparation, Properties and Uses

Silver nitrate or Lunar caustic (AgNO3)

Preparation

Silver nitrate is prepared by dissolving silver in dilute nitric acid.

3Ag + 4HNO3 ® 3AgNO3 + 2H2O + NO­

Properties

Physical

1.    It is soluble in water.

2.    Its aqueous solution may decompose on exposure to light.

Chemical Properties

1.    Action of Heat

On heating AgNO3 decomposes in two stages

2A gN O 3 --- 723 K -- > 2A gN O 2 + O 2    S ilv er n itrite

A gN O 2 --- 980 K -- >  Ag +  NO2

2. With NaCl

AgNO3 gives white precipitate of AgCl with soluble ionic chlorides.

AgNO3 + NaCl ® AgCl¯ + NaNO3

Silver nitrate is strongly caustic and oxidizing in nature.

4. With KBr & KI

AgNO3 gives pale yellow precipitate of AgBr with bromides and yellow AgI with iodides.

AgNO3 + KBr ® AgBr + KNO3

Yellow ppt

AgNO3 + KI ® AgI + KNO3

Yellow ppt

5. Action with organic compounds

Ammoniacal silver nitrate (Tollen's reagent) is reduced to silver mirror by

compounds like formic acid, formaldehyde or glucose

2AgNO3 + 2NH4OH ® Ag2O + 2NH4NO3 + H2O

Ag2O + HCOOH ® 2Ag¯ + H2O + CO2

Uses

1.     It is used in the preparation of silver halides which are extensively used in

2.     photography.

3.     It is used in silvering mirrors.

4.     It is used in preparation of marking inks and hair dyes. It is used for silver plating.

5.           It is used as laboratory reagent.