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Class 10ScienceChemical Substances – Nature and BehaviourChemical Reactions and EquationsEasy
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Why does copper powder turn black when heated in air?

Answer and explanation

Correct answer: Due to formation of black copper(II) oxide (CuO)

When copper powder is heated in air, it combines with oxygen and forms black copper(II) oxide: 2Cu + O₂ → 2CuO. The black CuO coating changes the appearance of the copper powder. Copper(I) oxide, Cu₂O, is red, copper carbonate is not formed under these conditions, and ordinary heating in air does not mean that copper melts; therefore option A is unambiguous.

Related tags

Class 10 ScienceCopper OxideOxidationChemical ReactionsChemical Reactions And EquationsChemical Substances – Nature And BehaviourChemical Substances Nature And BehaviourScience
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10 more MCQs
  1. 1What is the process called when one or more substances form new substances with different properties?
  2. 2Which of the following observations can be a common sign that a chemical reaction has occurred?
  3. 3What are the substances written on the left side of the arrow in a chemical equation called?
  4. 4What are the substances written on the right side of the arrow in a chemical equation called?
  5. 5Balancing a chemical equation is based on which law?
  6. 6What must be the same on the reactant and product sides of a balanced chemical equation?
  7. 7When two or more reactants combine to form a single product, what type of reaction is it?
  8. 8Calcium oxide reacts with water to form calcium hydroxide. What type of reaction is this?
  9. 9When a compound breaks down into two or more simpler substances, what type of reaction is it?
  10. 10When calcium carbonate is heated, it forms calcium oxide and carbon dioxide. What type of reaction is this?
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