Explain with examples what is meant by a 'mole' of a substance.

Write the name of the ${\mathrm{Na}}_2{\mathrm{SO}}_4$ compound and deduce its molecular mass.

Write the name of the ${\mathrm{K}}_2{\mathrm{CO}}_3$ compound and deduce its molecular mass.

Write the name of the ${\mathrm{CO}}_2$ compound and deduce its molecular mass.

Write the name of the ${\mathrm{MgCl}}_2$ compound and deduce its molecular mass.

Write the name of the $\mathrm{NaOH}$ compound and deduce its molecular mass.

Write the name of the ${\mathrm{AlPO}}_4$ compound and deduce its molecular mass.

Write the name of the ${\mathrm{NaHCO}}_3$ compound and deduce its molecular mass.

Two samples ‘m’ and ‘n’ of slaked lime were obtained from two different reactions. The details about their composition are as follows:

‘sample m’ mass: $7\mathrm{g}$, Mass of constituent oxygen: $2\mathrm{g}$, Mass of constituent calcium:$5\mathrm{g}$

‘sample n’ mass: $1.4\mathrm{g}$, Mass of constituent oxygen: $0.4\mathrm{g}$, Mass of constituent calcium: $1.0\mathrm{g}$

Which law of chemical combination does this prove? Explain.