Calculate VOLUME of H2 gas kept at S.T.P if it contains as many H atoms as in 98 gm of H3PO4

Explanation:

MOLAR mass of the PHOSPHORIC acid = 98 G/mole.  

Mass of the Phosphoric acid = 98 g.  

Therefore the   number of molecules of the Phosphoric acid = 6.022 × 10²³ molecules.

Hence,  

1 molecule of the Phosphoric acid have 3 atoms of Hydrogen.  

∴ 6.022 × 10²³ molecules of Phosphoric acid have 6.022 × 10²³ × 3 atoms of Hydrogen = 1.81 × 10²⁴ atoms.  

Hydrogen gas at S.T.P. also have the same number of atoms,  1.81 × 10²⁴ atoms.  

Therefore  Mass of the Hydrogen containing 1.81 × 10²⁴ atoms.

= Molar Mass × 1.81 × 10²⁴/Avogadro's number.  

= 2 × 1.81 × 10²⁴/6.022 × 10²³

= 2 × 3

= 6 g.  

 1 mole of any gas at S.T.P. occupies the volume of the 22.4 liter.

Therefore  2 g of the Hydrogen at S.T.P. occupies the volume of the 22.4 liter.

Therefore  6 g of the Hydrogen at S.T.P. occupies the volume of the 22.4 × 6/2 liter.  

= 22.4 × 3 = 67.2 liter.  

Hence, the volume of the Hydrogen at S.T.P. is 67.2 liter.