We shall see at first place what is mole,molar etc.It was believed in the past that all elements exist as atoms.Avogadro was the first person to postulate and prove that elements exist as molecules and do take part in reactions as molecule.As the atomic mass was measured in amu,so was mass of the molecule too measured.Since many elements contain isotopes in various proportion in nature, they exist in same proportion in a compound.e.g.
I like to share this Molar Entropy
Chlorine has isotopes with mass numbers 35,37 etc.It is not possible each time to find the chlorine isotope in the molecule of HCl, whether it is 35 or 37, and then find the molecular mass.Instead of that,the average mass of chlorine as it occurs in nature is found out [ which is 35.5], and taken as mass of chlorine. The mass of molecule so obtained is not called molecular but molar mass.The molar mass of the molecule when expressed in grams was termed as one mole.In other words a mole is the molar mass expressed in grams.
Molar VolumeAs seen above molar means that quantity which is associated with one mole of a substance.Volume is a property exhibited by gases and liquids and molar volume of a gas is volume occupied by a mole of gas.Is there any definition for ideal gas?Yes, it means the gas has perfect elastic collisions and without intermolecular attractions.As such they obey the gas laws perfectly.
The gas laws areBoyle's law stating that at fixed temperature the volume of a gas varies inversely with the pressure.PV="constant"Charles' law stating that the pressure and temperature vary inversely at fixed volume.P/T=constantWe get the universal gas law if both of the above are combined.P1V1/T1=P2V2/T2From the same, the Ideal gas law can also be derived,PV="nRT"Where P is pressure,V is volume,n is number of moles,R is gas constant and T is temperature.If the values of STP and n="1" and R are substituted,we getV="22.4" LThis is called as molar volume of an ideal gas.Thus an ideal gas at STP would measure 22.4 L.