You might have noted that when copper powder is heated in a china dish, the reddish brown surface of copper powder becomes coated with a black substance.(a) Why has this black substance formed?(b) What is this black substance?(c) Write the chemical equation of the reaction that takes place.(d) How can the black coating on the surface be turned reddish brown?
(a) The black coloured substance formed is due to the reaction of copper (Cu) with air, oxidation of copper takes place.
(b) The black substance is Copper (II) oxide.
(c) The chemical equation that takes place is given below:
$2Cu(s) + O_2 (g) → 2CuO(s)$
(d) On passing hydrogen gas over the heated material the black coating turns to reddish brown. The equation is given below:
$CuO(s) + H_2(g)→ Cu(s) + H_2O(l) $
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