Question

When the powder of a common metal is heated in an open china dish its colour changes to black . However when hydrogen is passed over the hot black substance so formed, it regains its original colour . Based on the above information answer the following questions..
1 what type of chemical reactions takes place in each of the two given steps ?
2,name the metal initially taken in the powder form . Write balanced chemical equations for both reactions.

Answer 1

metal initially taken is Cu
2Cu+O2---->2CuO (black)

when hydrogen is passed over CuO it regains its original color
CuO+H2 ----->Cu+H2O

Answer 2

Answer :

(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.

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.