Question

Calculate the number of atoms in each of the following :
(a) 52 moles of He,
(b) 52 Amu of He,
(c) 52 g Of He.

Answer 1

a) 1 mole of He contains $6.023\times {10}^{23}$ atoms
52 moles of He contains $52\times 6.023\times {10}^{23}$ atoms

b) Atomic mass of Helium is 4u = 2protons + 2 Neutrons = 1 atom
No. of atoms in 52u = $\frac{52}{4}$ = 13 atoms

c) 4g of He has 1 mole
1g of He has $\frac{1}{4}$ mole
52g of He has $\frac{1}{4}\times 52=13$ moles

1 mole=$6.022\times {10}^{23}$ atoms
so 13 moles means $13\times 6.023\times {10}^{23}$atoms