When the powder of a common metal is heated in an open china dish, its color turns black. However, when hydrogen is passed over the hot black substance so formed, it regains its original color. Based on the above information answer the following questions: (i) What type of chemical reaction takes place in each of the two given steps? (ii) Name the metal initially taken in the powder form. Write balanced chemical equations for both reactions.
Answers
Answer:
In open air, its is oxidised to form copper (II) oxide which is black in colour. The reaction is known as oxidation reaction. On passing hydrogen gas over the hot substance, the original colour of the metal is regained. It is an example of reduction reaction.
(1) In first step, oxidation reaction occurs and in second step, reduction reaction occurs.
(2) The name of metal is, copper (Cu) and the balanced chemical reaction will be,
Oxidation : 2Cu+O_2\rightarrow 2CuO
Reduction : CuO+H_2\rightarrow Cu+H_2O
Explanation :
Step 1 : When the powder of a cooper metal is heated in an open china dish its color changes to black.
In open air, its is oxidised to form copper (II) oxide which is black in colour. The reaction is known as oxidation reaction. On passing hydrogen gas over the hot substance, the original colour of the metal is regained. It is an example of reduction reaction.
The balanced chemical reaction is,
2Cu+O_2\rightarrow 2CuO
This is a oxidation reaction where oxygen is gained by the copper metal.
step 2 : When hydrogen is passed over the hot black substance that is (CuO), it regains its original color and form copper as a metal.
The balanced chemical reaction is,
CuO+H_2\rightarrow Cu+H_2O
It is a reduction reaction where hydrogen is gained by the cooper oxide.