(a) What are ionic compounds? List any four physical properties of these compounds.
(b) What reaction happens, when manganese dioxide is heated with aluminium powder? In which physical state is the metal produced in this reaction and why?
(a) The chemical bond formed by the transfer of electrons from one atom to another is known as an Ionic Bond and the compounds formed by such bonds are called Ionic Compounds.
Physical properties of ionic compounds:
- Ionic compounds are usually crystalline solids because their oppositely charged ions attract one another strongly and form a regular crystal structure.
- Ionic compounds have high melting points and high boiling points.
- Ionic compounds are highly soluble in water.
- Ionic compounds conduct electricity when dissolved in water or when melted because they contain charged particles i.e. ions.
(b) When manganese dioxide is heated with aluminium powder, manganese metal is produced.
3MnO2(s) + 4Al(s) → 3Mn(l) + 2Al2O3(s) + Heat
The reduction of manganese dioxide with aluminium is a highly exothermic reaction. A lot of heat is evolved therefore, the manganese metal produced is in molten state.