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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]

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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)

The number of moles = \(\frac{Given\,number\,of\,atoms}{Avogadro's\,number}\)

Number of moles = \(\frac{3.011\times10^{23}}{6.022\times10^{23}}\)

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 moles (n) = \(\frac{Given\,mass(m)}{Molar\,mass(M)}\)

Number of moles (n) = \(\frac{32g}{32g/mol}\)

Number of mole = 1 

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

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