Question

Q. Calculate the number of atoms in each of the following (i) 52 moles of Ar (ii) 52 u of He (iii) 52 g of He​

Answer 1

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(i) 1 mole of Ar =6.022×10^23

atoms of Ar

52 mol of Ar=52×6.022×10 ^23

atoms of Ar =3.131×10 ^25 atoms of Ar

(ii) Atomic mass of He = 4amu

Or

4amu is the mass of He atoms = 1

Therefore 52 amu is the mass of He atoms=0.25×52=13 atoms of He

(iii) Gram atomic mass of He = 4g

Or

4g of He contains =6.022×10 ^23

atoms

Therefore 52 g of He contains=

6.022×10 ^23/4×52 =7.83×10 ^24 atoms