Question

When Copper carbonate is heated it releases a brisk effervescence given by gas?
(a) \[C{O_2}\]
(b) \[{H_2}\]
(c) \[{H_2}S\]
(d) \[HCl\]

Answer 1

Hint: Effervescence is the formation of gas bubbles in a liquid by a chemical reaction. To solve this question we should know beforehand that Copper carbonate dissociates into two substances on being heated.

Complete step by step solution:
We know that thermal decomposition is a chemical reaction where a single substance breaks into two or more simple substances on being heated. The reaction is usually endothermic because heat is required to break the bonds present in the substance. This is why thermal energy must be supplied constantly for the reaction to keep going.
Copper carbonate decomposes into Copper oxide and Carbon dioxide on being heated.
Copper carbonate is green and copper oxide is black. We can see a color change from green to black during the reaction.
This is further illustrated by the following equation:
\[CuC{O_3} \to CuO\, + \,C{O_2}\]
Hence, the correct answer is Option (A) \[C{O_2}\]
We can prove this by shaking the gas evolved in a container containing lime water. We can observe that this gas turns the lime water milky. The gas produced must also be passed through acidified Potassium dichromate solution where it should not produce any observable change.

Additional information:
We should keep in mind that the metals which are near the bottom of the reactivity series their compounds generally decompose easily at high temperatures. This is because stronger bonds form between atoms towards the top of the reactivity series, and strong bonds break less easily.

Note: While testing for Carbon dioxide, we must remember to perform the acidified Potassium dichromate test after the lime water test as both Sulphur dioxide and Carbon dioxide turns lime water milky but Sulphur dioxide solution turns acidified potassium chromate solution green whereas carbon dioxide shows no change.