You might have noted that when copper powder is heated in a china dish, the
reddish brown surface of copper powder becomes coated with a black
substance.
(a) Identify the reaction that has occurred.
(b) Write the chemical name of the black substance formed.
(c) Write the chemical equation for the above reaction.
(d) How can the black coating on the surface be turned back to reddish
brown? Give necessary equation involved.

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Solution

Dear student,

1) The black coloured substance is formed due to the reaction of Cu with air.
2) Copper reacts with oxygen present in air to form copper oxide, which is black in colour. The black substance is the copper oxide.

3) 2Cu+O2→2CuO

Regards,

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You might have noted that when copper powder is heated in a Chine dish of copper powder becomes coated with black colour substance.

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(ii) What is that black substance?

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Q. You are given the following materials:
(i) Iron nails
(ii) Copper sulphate solution
(iii) Barium chloride solution
(iv) Copper powder
(v) Ferrous sulphate crystals
(vi) Quicklime

Identify the type of chemical reaction taking place when:
(a) Barium chloride solution is mixed with copper sulphate solution and a white precipitate is observed.
(b) On heating copper powder in air in a china dish, the surface of copper powder turns black.
(c) On heating green coloured ferrous sulphate crystals, reddish brown solid is left and smell of a gas having odour of burning sulphur is experienced.
(d) Iron nails when left dipped in blue colour copper sulphate solution become brownish in colour and the blue colour of copper sulphate fades away.
(e) Quick lime reacts vigorously with water releasing a large amount of heat.
Write chemical equations for each one of the above reactions.

(a) Explain the following in terms of gain or loss of oxygen with one example each :

(i) oxidation (ii) reduction

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Dear student, 1) The black coloured substance is formed due to the reaction of Cu with air. 2) Copper reacts with oxygen present in air to form copper oxide, which is black in colour. The black substance is the copper oxide. 3) 2Cu+O2→2CuO Regards,

Dear student,

1) The black coloured substance is formed due to the reaction of Cu with air.
2) Copper reacts with oxygen present in air to form copper oxide, which is black in colour. The black substance is the copper oxide.

3) 2Cu+O2→2CuO

Regards,