Question 1.1

Calculate the molecular mass of the following:

(i) H2O (ii) CO2 (iii) CH4

Answer:
 

(i) H2O

Molecular mass = Sum of atomic masses of all the elements in a molecule

= (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

(ii) CO2

Molecular mass = Sum of atomic masses of all the elements in a molecule

= (1 × Atomic mass of carbon) + (2 × Atomic mass of oxygen)

= [1(12.011 u) + 2 (16.00 u)] = 12.011 u + 32.00 u

= 44.01 u

(iii) CH4

Molecular mass = Sum of atomic masses of all the elements in a molecule

= (1 × Atomic mass of carbon) + (4 × Atomic mass of hydrogen)

= [1(12.011 u) + 4 (1.008 u)]

= 12.011 u + 4.032 u

= 16.043 u

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