Question

a) Calculate the relative molecular mass of water (H2O).
(b) Calculate the molecular mass of HNO3.

Answer 1

(a) Atomic mass of hydrogen = 1u,                               
                                    oxygen = 16 u 
       Molecular mass of water = 2 × 1+ 1×16                                                  
                                                  = 18 u
(b) The molecular mass of HNO3 = 1 + 14 + 48  
                                                      = 63 u

Answer 2

1 the molecular mass of water is:-
   relative mass of hydrogen=1u
   relative mass of oxygen=16u 
   ∴ (2 × Atomic mass of hydrogen) + (1 × Atomic mass of oxygen)
⇒ [2(1.0084) + 1(16.00 u)]
⇒ 2.016 u + 16.00 u
⇒18.016
⇒ 18.02 u
2 molecular mass of hno3 is:-
   hydrogen=1u
   nitrogen=14u
    oxygen=16u
    ∴(1 × Atomic mass of hydrogen) + (1 × Atomic mass of oxygen)+(3 × Atomic mass of oxygen)
⇒1+14+48
=63g/mol