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Question
1 g of copper powder was taken in a China dish and heated. What change takes place on heating? When hydrogen gas is passed over this heated substance, a visible change is seen in it. Give the chemical equations of reactions, the name and the color of the products formed in each case.
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Solution
When copper powder in a china dish is heated in air, copper undergoes surface oxidation by reacting with the oxygen present in the air to form a copper oxide and forms a black layer on top.
\[\ce{2Cu(s) + O2(g)->[Heat]\underset{\text{Black colour}}{2CuO(s)}}\]
When hydrogen gas is passed over the hot copper oxide, it reacts with hydrogen gas to form elemental copper and water will be produced in the liquid state.
\[\ce{CuO(s) + H2(g)->Cu(s) + H2O(l)}\]
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