CBSE Class 11-science Answered

See, one mole is a unit for measurement of number of atoms of molecules.

This is same like you measure mass in kg or g or volume in litre or mL.

Mole concept for atom an molecule is different.

for an atom,

If we find equivalence of one mole,

1 mole of an atom contain 6.022 x 10²³ atoms. The mass of 1 mole of an atom is equal to its gram atomic mass.

For example, if we want 1 mole of oxygen atom, we will have to collect 6.022 x 10²³ atoms of oxygen.

The mass of all these atoms collectively will be 16 g.

For a molecule,

1 mole of a molecule will contain 6.022 x 10²³ molecules.

The mass of 1 mole of molecule is equal to its gram molecular mass.

For example, if we want 1 mole of oxygen molecule (O₂), we will have to collect 6.022 x 10²³ molecules of oxygen.
The mass of all these molecules collectively will be 32 g.

The volume of 1 mole of oxygen molecule will be 22.4 litres at STP.

Now to apply this in numericals, see whatever is asked in the question take that relationship and apply unitary method to find the answer.

Example: If number of atoms in 22 g of oxygen atoms is asked.

Take the relation as,

16 g of oxygen atoms will contain =  6.022 x 10²³ atoms of oxygen

22g of oxygen atoms will contain =  [(6.022 x 10²³ x 22 ) / 16 ] atoms of oxygen

Similarly all the questions can be solved. If any specific numerical do ask.