Question

Copper carbonate decomposes to copper oxide and carbon dioxide. Guess the color of the residue:
A. Blue
B. Black
C. Yellow
D. White

Answer 1

The answer to this question lies in the fact that copper carbonate decomposes into copper oxide and carbon dioxide when it is subjected to thermal conditions, there occurs a change in colour and this reaction is thermal degradation. The answer is obtained if you know the original colour of copper carbonate.

Complete answer:
From your chemistry lessons you have learned about the thermal decomposition reaction and the change of color that takes place in the reaction.
Thermal decomposition reaction is a type of reaction which takes place in presence of heat. In reaction the breakdown of reactants takes place formic one or more than product from one reactant when the reactant is heated.
In thermal decomposition reactions many metal carbonations take place like copper, calcium, etc.
In this question we will see the thermal decomposition reaction taking place in Copper carbonate which is a metal carbonate. So copper carbonate$(CuC{{O}_{3}})$ on being heated breaks into two products that are copper oxide $(CuO)$ and carbon dioxide $(C{{O}_{2}})$
So, the reaction of copper carbonate is given as:
$CuC{{O}_{3}}\to CuO+C{{O}_{2}}$
Here, the copper carbonate is green in color and after the reaction the residue copper oxide is of black color. So, during the reaction we can see the color change in the color of the reactant and the residue or the product. And to check the carbon dioxide that is produced in the reaction we can use limewater. When we shake the gas which has evolved in the container that contains the lime water we will see that the lime water turns milky due to the gas. Therefore the color of the residue will be black.

Thus the correct option will be (B).

Note: Thermal decomposition reaction is a type of endothermic reaction and endothermic reaction is a type of reaction that gains energy from the surrounding. Therefore during the thermal decomposition reaction we have to supply thermal energy constantly to keep the reaction going. In an exothermic reaction energy is given out to the surrounding.