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

`(i) 3.131 xx10^(25) "atoms " (ii) 13 "atoms " (iii) 7.8286 xx10^(24) "atoms"`

Explanation

(i) 1 mole of Ar `=6.022 xx10^(23) ` atoms of Ar
`therefore ` 52 mol of `Ar =52 xx6.022 xx 10^(23)` atoms of Ar
`=3.131 xx 10^(25)` atoms of Ar
(ii) 1 atoms of He =4 u of He
Or ,
4 u of He = 1 atoms Of He
1 u of He `=(1)/(4)` atom of He
52 u of He `=(52)/(4)` atom of He
=13 atoms of He
(iii) 4 g of He `= 6.022 xx10^(23)` atoms of He
` therefore ` 52 g of He `=(6.022xx10^(23)xx52)/(4)` atoms of He
`=7.8286 xx 10^(24)` atoms of He