Q. 22

What is meant by the term ‘mole’? Calculate the number of moles in

(a) 3.011 × 1023 atoms of C

(b) 32 g of oxygen gas

[NA = 6.022 × 1023 mol–1, At. mass of O = 16 u and C = 12 u]

Answer :

Mole: One mole of any species (Atoms, molecules, ions or particles) is that quantity in number having a mass equal to its atomic or molecules mass in grams.


(a) We will convert 1.0505 × 1023 atoms of C into number of moles:


We know, 1 mole = 6.022 × 1023(Na = Avogadro’s number)




Number of moles = 0.5


Thus, the number of moles in 3.011 × 1023 atoms of C is 0.5.


(b) Given mass: 32g


Molar mass of oxygen gas (O2) = 2 × atomic mass of oxygen = 2 × 16 u = 32g /mol


To calculate the number of moles, we will apply the formula given below:




Number of mole = 1


Thus, the number of mole in 32 g of oxygen gas is 1.


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