To perform and observe the action of heat on crystals of ferrous sulphate and classify the reaction.

 AIM: To perform and observe the action of heat on ferrous sulfate crystals and classify the reaction.

Materials Needed

Ferrous sulfate crystals (FeSO₄·7H₂O), Bunsen burner, Test tube, Test tube holder, Safety goggles, Heat-resistant mat or stand.

THEORY

Ferrous sulfate (FeSO₄·7H₂O) is a blue-green crystalline compound. When heated, it undergoes dehydration and decomposition.

The action of Heat on Ferrous Sulfate

1. Dehydration:

   • Reaction: ​FeSO₄.7H₂O(s)   →(heat)   FeSO₄(s) + 7H₂O
   • Observation: The green crystals lose water and turn white.
   • Type of Change: Physical change (loss of water).

2. Decomposition:

• Reaction:2FeSO₄(s)      →(heat)           Fe₂O₃(s)      +  SO₂(g) + SO₃(g)​
• Observation: The white powder turns brown, releasing sulfur dioxide (SO₂) and sulfur trioxide (SO₃) gases.
• Type of Change: Chemical change (formation of new substances).

PROCEDURE

Step 1: About 5 g ferrous sulphate crystals in a dry boiling tube is taken.

Step 2: The colour of the ferrous sulphate crystals is noted.

Step 3: The boiling tube is heated.

Step 4: The colour of the crystals after heating is observed.

Step 5: A gas is evolved which is smelled.

Step 6: A wet blue litmus paper is brought near the mouth of the boiling tube.

Observations

• Color Change: The green crystals turn white as they lose water, and then turn brownish upon further heating.
• Decomposition: A gas with a characteristic pungent odor (SO₂) is released during the decomposition.

Inference

1.When heated, ferrous sulphate crystals are decomposed to produce Ferric oxide, sulphur dioxide and sulphur trioxide.

2. Such reactions are called decomposition reaction.

Precautions

• Always wear safety goggles while performing the experiment.
• Use a test tube holder to hold the test tube to avoid burns.
• Conduct the experiment in a well-ventilated area or under a fume hood to avoid inhaling gases produced during decomposition.