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प्रश्न
State the change in colour observed in following case mentioning the reason:
Copper powder is strongly heated in air.
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उत्तर
Copper powder turns from brown to black when heated vigorously in the presence of oxygen because oxygen reacts with copper powder to form copper oxide, which has a dark colour. Thus, the appearance of copper oxide is what causes the colour change.
\[\ce{2Cu(brown) +O2 ->2CuO(black)}\]
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\[\ce{MnO_2 + 4HCl->MnCl_2 +2H_2O + Cl_2}\]
