Precipitation and thermal decomposition of copper(II) hydroxide
Make blue copper(II) hydroxide, then heat it and watch it decompose to black copper(II) oxide.
Objectives
- Carry out a precipitation reaction.
- Observe a thermal decomposition.
- Write balanced equations for both.
Theory
Copper(II) ions react with hydroxide ions to give insoluble blue copper(II) hydroxide. On heating, the hydroxide loses water and forms black copper(II) oxide — one substance breaking down into two is a decomposition reaction.
CuSO₄ + 2NaOH → Cu(OH)₂↓ + Na₂SO₄ Cu(OH)₂ → CuO + H₂O
Procedure
- Put on your safety goggles and lab coat.
- Place a beaker and add about 30 mL of copper(II) sulfate solution.
- Add sodium hydroxide solution until a blue precipitate forms.
- Place a Bunsen burner and move the beaker onto its tripod.
- Light the burner and heat the mixture.
- Keep heating until the precipitate turns black.
- Turn off the burner.
Precautions
- Sodium hydroxide is corrosive.
- Heat gently and do not boil dry.
- Subject
- Chemistry
- Grade
- 10–11
- Chapter
- Chemical Reaction (Nepal National Curriculum (CDC), grade 10)
- Difficulty
- Medium
- Duration
- 20 min
- Safety level
- Medium
- Version
- 1.0
Apparatus
- Beaker (250 mL)
- Bunsen burner with tripod
Chemicals
- Copper(II) sulfate solution CuSO₄ Harmful
- Sodium hydroxide solution NaOH Corrosive
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