Question

A reddish brown metal heated strong turns black. when hydrogen is passed over black substance it, regain its original colour.
1. Name the metal and the black colour substance.
2. Iron oxide react with aluminium powder. Give one practical application of this reaction.

Answer 1

The metal in reddish brown colour is Copper (Cu).         On heating it forms black colored oxide       2Cu + O₂ → CuO Cu on reaction with conc.H₂SO₄ produces SO₂ gas (pungent smelling gas) Cu + 2H₂SO₄ → CuSO₄ + SO₂ + 2H₂O Copper oxide on reaction with dil.H₂SO₄ forms copper sulphate CuO + H₂SO₄ → CuSO₄ + H₂O (blue colored solution) X = Cu Y = CuO Z = CuSO₄ + H₂O Cu reacts with dil.HNO₃ to liberate nitrogen monoxide Cu + HNO3 →Cu (NO3)2 + H2O + NO (colourless gas) Cu reacts with conc.HNO₃ to liberate nitrogen dioxide Cu + 2HNO3 → Cu (NO3)2 + H2O + NO2 (brown colored gas)     A =NO B = NO2