Question

State the Methods to Calculate Number of Mole.

Answer 1

5. If volume of gas is given along with its temperature (T) & pressure (P) then n = PV/RT

where R = 0.0821 lit-atm/mol K & P is in atmosphere, T in Kelvin and V in litre 

Note: 

1. Do not use the above expression for solids/liquids for eg. H₂O at 10 °C. 

2. 1 gm - atom is same as 1 mole of an atom & hence will have weight equal to atomic weight expressed in grams. 

3. 1 gm – molecule is same as 1 mole of the molecule & hence will have weight equal to molecular weight expressed in gms.

 4. 1 gm – Ion is same as 1 mole of an ion & hence will have weight equal to ionic weight 

5. Remember 1 gm of atom & 1 gm– atom are two different phrases. Former is mentioning weight (equal to 1 gm) & latter is mentioning moles.

For Example: 

(1) x g atom of nitrogen = x moles of N atom = X x N_A number of N atoms

(2) x g molecule of nitrogen = x moles of N₂ molecules = X x N_A molecules of N₂ = 2x x N_A number of N atoms.