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Experiment No. N

Analysis of Cobalt(II) Nitrite (Co(NO₂)₂)

Aim

To determine the presence of anion and cation in the given salt

Preliminary Test

  • Odor: Odorless
  • Texture: Crystalline
  • Color: White
  • Solubility: Soluble in water

Test of Anion

ExperimentObservationInference
Warm the solid salt with dilute H₂SO₄Brown fumes of NO₂ are evolvedNO₂⁻ may be present
Confirmatory Tests
Potassium Iodide Starch Test
Take evolved gas and add KI + starch solution acidified with acetic acid		Blue colour appearsNO₂⁻ is confirmed
Sulphanilic Acid / 1-Naphthylamine Test
Acidify 1 mL of water extract with acetic acid and add sulphanilic acid solution followed by 1-naphthylamine reagent		Red colour is formedNO₂⁻ is confirmed

Test of Cation

ExperimentObservationInference
Original solution + H₂S gas in presence of NH₄OHBlack precipitate is formedGroup IV cation may be present
Dissolve the black sulphide precipitate in aqua regia and heatResidue remains in solution after evaporationCo²⁺ may be present
Confirmatory Test
Potassium Hexanitritocobaltate(III) Test
Neutralise with NH₄OH, acidify with dilute acetic acid and add strong potassium nitrite solution		Yellow precipitate is formedPresence of Co²⁺ is confirmed

Result

The given salt contains Co²⁺ ions as cation and NO₂⁻ ions as anion. The salt is Co(NO₂)₂.

Precautions

  1. Handle the chemicals with care.
  2. Don't use excess of chemicals.
  3. Keep the mouth of the test tube away from the face.