Question

Calculate the number of moles in each of the following:
(i) 100 g of H2O (ii) 78 mg of CO2 (iii) 66 µg of CH4

Answer 1

The number of moles in

(i) 100 g of H2O

Molecular mass of water, H2O: 18.02 g/ moles

Number of moles=100g/ 18.02 g/ moles= 5.55 moles

(ii) 78 mg of CO2

Gram molecular weight of CO2 = 12+2 × 16 = 44g.

Number of moles=78 mg/44 g/ moles= 0.00177 moles

(iii) 66 ug of CH4

Gram molecular weight of CH4 = 16.04 g/mol

Number of moles= 66 ug/16.04 g/ moles= 4.125u moles