Detecting carbon and hydrogen in an organic compound

Steps

1. Mix a little of the organic substance (cloth, leather, paper or plastic) with dry copper(II) oxide powder in a heat-resistant test tube.
2. Heat the tube and pass the vapours first over white anhydrous copper sulphate, then into clear limewater.

Observations, explanation and conclusion

• White CuSO₄ turns blue because it absorbs water vapour ⟹ the compound contains hydrogen.
• Limewater turns milky because CO₂ is liberated ⟹ the compound contains carbon.
• CuO oxidises the elements of the compound: C + 2CuO → CO₂ + 2Cu, and 2H + CuO → H₂O + Cu.