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Thermal Decomposition of Ferrous Sulphate

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Aim

To observe the thermal decomposition of ferrous sulphate crystals.

Materials Required

Ferrous sulphate crystals (FeSO₄.7H₂O)
Dry boiling tube
Bunsen burner
Test tube holder (tongs)

Theory

Ferrous sulphate crystals (FeSO₄.7H₂O) are pale green in colour. When heated, they first lose water of crystallisation and turn white/colorless.

On further heating, anhydrous ferrous sulphate decomposes to form solid ferric oxide (Fe₂O₃), sulphur dioxide (SO₂) gas, and sulphur trioxide (SO₃) gas. This is a thermal decomposition reaction.

Chemical Equation:
2FeSO₄ (s) + Heat → Fe₂O₃ (s) + SO₂ (g) + SO₃ (g)

Procedure

  1. Take about 2 g of ferrous sulphate crystals in a dry boiling tube. Note their original green color.
  2. Hold the boiling tube with a test tube holder and heat it over the flame of a burner.
  3. Observe the colour of the crystals after heating.
  4. Carefully smell the gas being emitted using a wafting motion. (Do not inhale directly).

Precautions

Status: Ready
Color: None

Observation Table

S.No. Stage Observation

📹 Experiment Video

Knowledge Check

1. What is the original colour of ferrous sulphate crystals?

2. Upon heating, the green crystals first turn white. Why?

3. What is the final colour of the residue left in the tube after strong heating?

4. Which gases are evolved during this decomposition?

5. What type of reaction is this?

Lab Report Summary

Experiment: Thermal Decomposition of Ferrous Sulphate

Aim: To observe the thermal decomposition of ferrous sulphate crystals.

Result:

Ferrous sulphate crystals (pale green) first lose water on heating, turning white. On further heating, they decompose into reddish-brown ferric oxide (Fe₂O₃) while emitting SO₂ and SO₃ gases (pungent sulphur smell). This is a thermal decomposition reaction.