Calculate the number of moles for the following:
(i) 52 g of He (finding mole from mass)
(ii) `12.044 × 10_(23)` number of He atoms (finding mole from number of particles).

Explanation

No. of moles = n
Given mass = m
Molar mass = M
Given number of particles = N
Avogadro number of particles = `N_(0)`
(i) Atomic mass of He = 4 u
Molar mass of He = 4g
Thus, the number of moles
= `("given mass")/("molar mass")`
`⇒ n = (m)/(M) = (52)/(4)=13`
(ii) we know,
1 mole = `6.022 × 10_(23)`
The number of moles
= `("given number of particles")/("Avogadro number")`
`implies n = (N)/(N_(o)) = (12. 044xx10^(23))/(6.022xx10^(23))=2`