Question

A white solid which gives a yellow residue on heating is:
a.) Copper sulphate
b.) Hydrogen sulphide
c.) Copper oxide
d.) Lead carbonate

Answer 1

Hint: The concept to be used is of thermal decomposition. When a compound is heated,it undergoes a chemical change resulting in the formation of different metals and in the liberation of different gas.
Out of all the options, lead carbonate \[\left( PbC{{O}_{3}} \right)\] is a white solid substance which when undergone thermal decomposition turns into a yellow solid.

Complete step by step answer:
The thermal decomposition of different compounds takes place at different temperatures. Some decompose at lower temperature to give their constituent metals, fumes,compounds or gases and some at a higher temperature.
In our case ,lead carbonate \[\left( PbC{{O}_{3}} \right)\] is a solid ,white colored compound which is toxic when exposed thermal decomposition breaks into a yellow colored compound \[PbO\] with the liberation of carbon dioxide gas.This reaction takes place at a temperature of over \[{{315}^{o}}C\] . The reaction is as follows
\[PbC{{O}_{3}}\to PbO+C{{O}_{2}}\left( gas \right)\]
So, the correct answer is “Option D”.

Additional Information:
Hydrogen sulphide is a colorless gas which when exposed to heat breaks down into toxic gases like \[S{{O}_{2}}\].
copper sulphate and copper oxide are blue crystalline and black color solids which give different colored constituents.
Copper sulphate turns white on heating due to the loss of water of crystallization.
Copper \[\left( 11 \right)\] oxide decomposes to copper \[\left( 1 \right)\] on heating to \[{{1026}^{o}}C\] which further decomposes to copper and oxygen at \[{{1800}^{o}}C\].

Note: Water of crystallization or water of hydration are water molecules that are present inside crystals. Water is often incorporated in the formation of crystals from aqueous solutions. In some contexts, water of crystallization is the total mass of water in a substance at a given temperature.
The salt which has water of crystallization is known as a hydrate.
Thermal decomposition of one type of a chemical reaction. Others are redox,double displacement and displacement reactions.