Study Guides/Chemistry/Colour of Ferrous Sulphate and Lead Nitrate
Study Guide · Chemistry

Colour of Ferrous Sulphate and Lead Nitrate

In Class 10 Chemistry, thermal decomposition reactions are very important. Two of the most frequently tested experiments involve heating Ferrous Sulphate (FeSO₄) and Lead Nitrate (Pb(NO₃)₂). Remembering their colours is crucial for exam questions.

Question (Click to Flip)

What is the colour of ferrous sulphate crystals?

Answer

Ferrous sulphate crystals (FeSO₄·7H₂O) are pale green in colour.

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Key Facts

Ferrous Sulphate initial: Pale Green.

Ferrous Sulphate after heating: Reddish-Brown residue + burning sulphur smell.

Lead Nitrate initial: White powder.

Lead Nitrate after heating: Yellow residue + Brown fumes of NO₂ gas.

1. Ferrous Sulphate (FeSO₄)

  • Initial Colour: The crystals of ferrous sulphate heptahydrate (FeSO₄·7H₂O) are Pale Green.

What happens on heating?

  • First, it loses water to become anhydrous FeSO₄, which turns White.
  • On strong heating, it decomposes to form Ferric Oxide (Fe₂O₃), Sulphur Dioxide (SO₂), and Sulphur Trioxide (SO₃).
  • Final Colour: The residue (Fe₂O₃) is Reddish-Brown.
  • Smell: A characteristic smell of burning sulphur (due to SO₂ gas).

2. Lead Nitrate (Pb(NO₃)₂)

  • Initial Colour: Lead nitrate powder is Colourless or White.

What happens on heating?

  • On strong heating, it decomposes to form Lead Oxide (PbO), Nitrogen Dioxide (NO₂), and Oxygen (O₂).
  • Observation 1: Dense Brown Fumes are emitted (this is the NO₂ gas).
  • Final Colour: The residue of Lead Oxide (PbO) is Yellow when cold (and reddish-brown when hot).

Questions and Answers

What is the colour of ferrous sulphate crystals?+

Ferrous sulphate crystals (FeSO₄·7H₂O) are pale green in colour.

What is the colour of lead nitrate?+

Lead nitrate is a white or colourless powder.

What gas produces brown fumes when lead nitrate is heated?+

Nitrogen dioxide (NO₂) gas produces the brown fumes when lead nitrate is heated.

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