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.

Solution

(i) 52 moles of Ar.

because space space 1 space mole space Ar space contains space 6.02 space cross times space 10 to the power of 23 space atoms therefore space space space 52 space moles space Ar space would space contain space equals space 6.02 space cross times space 10 to the power of 23 cross times 52 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space 3.1304 space cross times space 10 to the power of 25 space atoms

(ii) 52u of He.
Atomic mass of He = 4u
i.e. 4u of He = 1 atom He

therefore

52 u He

equals space 1 fourth cross times 52 space equals space 13 space atoms space of space He

(iii) 52 g of He.
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