Question

When zinc carbonate is heated and cooled, the change(s) that are observed are:
(a)- Physical change
(b)- Nuclear change
(c)- First chemical and then physical change
(d)- First physical and then chemical change

Answer 1

Hint: If the reactants change to form products then it is a chemical change. If the substance remains the same but its physical properties like color, size, etc changes, then it is a physical change. When zinc carbonate is heated, the carbon dioxide escapes, and when cooled the color changes.

Complete step by step answer:
Zinc carbonate is an inorganic compound. The formula of zinc carbonate is $ZnC{{O}_{3}}$. The physical form of zinc carbonate is a solid white powder or it may by white crystalline solid. Zinc carbonate is insoluble in water.
When the zinc carbonate is heated, it is converted into zinc oxide. There is the removal of carbon dioxide gas. The reaction is given below:
$ZnC{{O}_{3}}\to ZnO+C{{O}_{2}}\uparrow $

So, when the zinc carbonate is heated, the reactant is changed into products. Hence it is a chemical change. So, now the formed zinc oxide is cooled, then the substance remains the same. The color of hot zinc oxide is yellow, but when it is cooled the color changes to white. The reaction is:
$\underset{yellow}{\mathop ZnO}\,\to \underset{white}{\mathop ZnO}\,$

Since the reactant and product are the same it is not a chemical change. As the color changes, it is a physical change. So, first, there is a chemical change and then physical change.
So, the correct answer is “Option C”.

Note: The other names of zinc carbonate are calamine or smithsonite. The boiling point of zinc carbonate is ${{333.6}^{\circ }}C$. It is basic in nature. Since it is insoluble in water, but it is soluble in dilute acids and alkalis.