Question

What is the colour of \[PbO\] and \[ZnO\] (They are the residues)?

Answer 1

Hint: We will first understand some physical properties of \[PbO\] and \[ZnO\], then to the final answer.

A chemical change is defined as the transformation of one chemical substance into one or more other chemical compounds. Chemical processes cause these changes, as molecules and ions rearrange themselves to form various structures and so have different properties.
In general, most reactions are irreversible in nature but some reactions are reversible.

Complete step by step solution:
\[Pb{O_2}\] is lead oxide also known as anhydrous plumbic acid or plumbic oxide. It is dark brown in colour and is in crystalline powdered form.
When lead oxide is heated it forms lead monoxide and oxygen.
\[PbO{}_2 \to PbO + {O_2}\]
Lead monoxide is the residue form which is yellow in colour.
Zinc oxide (\[ZnO\]) is an amphoteric substance that combines with acids to produce zinc salts and strong alkalis to produce zincates.
Zincate is found in the earth’s crust containing magnesium and other impurities. This zinc ore or zinc oxide reacts both with acid and base and is hence amphoteric in nature.
Zinc Oxide is white in colour but when heated at a high temperature nearly \[{800^o}C\]its colour change to yellow. As it cools down its again changes to white colour.
This shows a reversible reaction.
Hence, the colour of \[PbO\] and \[ZnO\] is yellow.

Note: Candidates generally get confused with colour change. The change of colour of chemical substances on heating is a chemical change, not a physical change. There are a few things to keep in mind while making chemical changes- colour change, precipitation, formation of gas or gas bubbles, odour or flavour change, volume change, light production, and many other changes are examples.

A few factors should be kept in mind when making a physical change- alterations in size and volume, alterations in density and mass, alterations in pressure, alterations in temperature, and alterations in texture and elasticity.