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A student performs the following experiment in his school laboratory. List two observations to justify that in this experiment a chemical change has taken place.

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Two observations that indicate a chemical change are: (1) Formation of a new substance, such as a gas, precipitate, or color change. (2) Release or absorption of energy, like heat, light, or sound, during the reaction.

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  1. ANSWER: Observations to justify chemical change:

    1. Effervescence (bubbling) is observed due to the evolution of hydrogen gas when zinc reacts with dilute sulphuric acid.
    2. Zinc granules gradually dissolve and a new substance, zinc sulphate solution, is formed.

    Hence, gas evolution and formation of a new product confirm that a chemical change has taken place.

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