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ICSE Class 8 Chemistry Question 5 of 5

Physical and Chemical Changes — Question 3

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Question 3

Give reasons why the following are considered as chemical changes.

  1. Copper carbonate on heat gives copper oxide and carbon dioxide.

  2. A bright light is seen evolved when a strip of magnesium is heated.

  3. Sulphur when burnt in air evolves a gaseous acidic product.

  4. An iron nail kept open in the atmosphere rusts.

  5. A piece of magnesium strip is dropped into a beaker containing dilute hydrochloric acid.

Answer

  1. Copper carbonate on heating gives copper oxide and carbon dioxide. As new products are formed and the change is irreversible hence it is a chemical change.

  2. When a strip of magnesium is heated, magnesium oxide is produced and the bright light seen is the evolution of energy in the form of light. Hence, it is considered a chemical change.

  3. Sulphur burns in air to produce a new gaseous acidic product [sulphur dioxide]. Hence, the change is a chemical change.

  4. Iron nail kept in air forms rust [iron [III] oxide]. Iron [III] oxide is a new product and has different chemical composition and properties as compared to that of an iron nail. Hence, the reaction is a chemical change.

  5. When a piece of magnesium strip is dropped into a beaker containing dilute hydrochloric acid, magnesium chloride is formed and hydrogen gas is liberated. As new products are formed and the change is irreversible hence it is a chemical change.