Synthesis of sodium cobalt(III) nitrite from Co(II) salt and NaNO₂ salts.

Synthesis of Sodium Cobalt(III) Nitrite

Aim

To synthesize sodium cobalt(III) nitrite from a cobalt(II) salt using sodium nitrite.

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Principle

Sodium cobalt(III) nitrite is prepared by oxidation of cobalt(II) ions to cobalt(III) in the presence of excess nitrite ions (NO₂⁻).

In acidic medium, sodium nitrite acts as both ligand and oxidizing agent forming the complex salt sodium hexanitritocobaltate(III).

The reaction forms a yellow crystalline precipitate of sodium cobaltinitrite.

Reaction

$$Co^{2+} + 6NO_2^- \rightarrow [Co(NO_2)_6]^{3-}$$
$$3Na^+ + [Co(NO_2)_6]^{3-} \rightarrow Na_3[Co(NO_2)_6]$$

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Requirements

Chemicals

Cobalt(II) chloride / cobalt(II) nitrate
Sodium nitrite (NaNO₂)
Acetic acid
Distilled water
Ethanol

Apparatus

Beaker

Glass rod

Measuring cylinder

Funnel

Filter paper

Water bath

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Procedure

1. Take about 2 g of cobalt(II) salt in a beaker and dissolve it in 10–15 mL distilled water.

2. Add excess sodium nitrite solution slowly with constant stirring.

3. Add a few drops of acetic acid to maintain slightly acidic medium.

4. Heat the mixture gently on a water bath for 10–15 minutes.

5. A yellow crystalline precipitate of sodium cobalt(III) nitrite begins to form.

6. Allow the solution to cool.

7. Filter the precipitate using filter paper.

8. Wash the crystals with cold water followed by ethanol.

9. Dry the crystals between filter papers.

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Observation

Observation	Result
Colour of cobalt salt solution	Pink
Colour of precipitate formed	Yellow
Nature of crystals	Yellow crystalline solid

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Result

Sodium cobalt(III) nitrite [Na₃[Co(NO₂)₆]] was successfully synthesized as yellow crystals.