Copper powder heated turns black; how the change is reversed

The same question, asked 4 times: 2023*, 2024*, 2025*, 2026. Every wording below, oldest first.

Try each one first, then open its answer.

Question 1
2023
21 (b) $When copper powder is heated in a watch glass, a black substance is formed. (i) Why is this black substance formed ? Name it. (ii) How can this black substance be reversed to its original form ?$
Question 2
2023
31 $A reddish brown metal used in electrical wires when powdered and heated strongly turns black. When hydrogen gas is passed over this black substance, it regains its original colour. Based on this information answer the following questions - (a) Name the metal and the black substance formed. (b) Write balanced chemical equations for the two reactions involved in the above information.$
Question 3
2024
21 (a) $Copper powder is taken in a china dish and heated over a burner. Name the product formed and state its colour. Write the chemical equation for the reaction involved.$
Question 4
2025
27 $State the change that is observed when a China dish containing copper powder is heated over the flame of a burner. Name the phenomenon responsible for the change and write balanced equation for the chemical reaction that occurs. How is this reaction different from the reaction that occurs when copper wares kept in open air slowly lose their shiny brown surface and gain a coat ? Write chemical name of the coating and state its colour.$
Question 5
2025
26 $A copper wire on burning in flame, gets coated with a black substance. Write the chemical equation of the reaction that takes place. How can this chemical change be reversed ?$
Question 6
2026
27 $\mathrm{H_2}$

Copper powder heated turns black; how the change is reversed

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