Utility of mole concept:
(i) Form the number of moles of a substance, we can calculate the number of elementary particles because the number of moles of a substance is directly proportional to the number of elements particles.
(ii) One mole of a gas occupies 22.4 litres at S.T.P
(iii) One mole of any gas under the same conditions of temperature and pressures occupies the same volume
(iv) One mole is equal to molecular mass in grams which is equal to 6.022 x 10²³ atoms, molecules, ionsetc.Thus, we can calculate absolute masses of atoms and molecules.

(i) According to Dalton's atomic theory, matter is invdivisible, i.e which cannot be divided.But now it is known that under special circumstances, atoms can be divided into still smaller particles called electrons, protons and neutrons.
(ii) Dalton's atomic theory fails to explain why substances like charcoal, graphite and diamond have different properties when all these substances are made up the same type of atoms, called carbon atoms.
(iii) Dalton's atomic theory postulated that all the atoms of the same element have exactly the same mass.It is now known that isotopes are atoms of the same element but have different masses.
(iv) It is known that some atoms called isobars have same masses but these belong to different elements.whereas Dalton's atomic theory says that atoms of different atoms have different masses.

(i) Mass of 1 mole CO₂ = 12 + 32 = 44 u
Mass of 5 moles CO₂ = 44 x 5 = 220 u
Mass of 1 mole of H₂O = 2 + 16 = 18 u
Mass of 5 moles of H₂O = 5 x 18 = 90 u
(ii) 40 g calcium make = 1 mole
240 g calcium make = \(\frac { 240 }{ 40 } \) = 6 moles
24 g magnesium make = 1 mole
240 g magnesium make = \(\frac { 240 }{ 24 } \) = 10 moles
Ratio of 240 g calcium and 240 g magnesium in moles = \(\frac { 6 }{ 10 } \) or 3 : 5