Detecting carbon and hydrogen in an organic compound

• Experiment: mix a small sample of an organic substance (sugar, paper, wool, plastic) with dry copper(II) oxide in a hard-glass tube and heat strongly.
• Pass the gases first over anhydrous white copper(II) sulphate and then through lime water.

Observations:

1. The white anhydrous CuSO₄ turns blue — water vapour was formed (hydrogen of the compound combined with oxygen of CuO).
2. The lime water turns milky (turbid) — carbon dioxide was formed (carbon of the compound combined with oxygen of CuO).

Conclusion: the compound contains carbon and hydrogen.

C + 2CuO → CO₂ + 2Cu 2H + CuO → H₂O + Cu (more exactly: organic H → H₂O) CO₂ + Ca(OH)₂ → CaCO₃↓ + H₂O CuSO₄ (white) + 5H₂O → CuSO₄·5H₂O (blue)