Problems on mole concept | part- 1
Example 1: Calculate the number of moles for the following:
(i) 52 g of He (finding mole from mass)
(ii) 12.044 × 10^{23}
Sol:
No. of moles = n
Given mass = m
Molar mass = M
Given a number of particles = N
Avogadro number of particles = N_0
(i) The atomic mass of He = 4 u
Molar mass of He = 4 g
Thus, the number of moles = \frac{given\:mass} {molar\:mass}
n = \frac{m}{M}
(ii) we know, 1 mole = 6.022 × 10^{23}
The number of moles = \frac{given\:a\:number\:of\:particles }{Avogadro\:number}
n = \frac{N}{N_0}
Example 2: Calculate the mass of the following:
(i) 0.5 mole of N_2
(ii) 0.5 mole of N atoms (mass from a mole of an atom)
(iii) 3.011 × 10^{23}
(iv) 6.022 × 10^{23}
Sol:
(i) mass = molar mass × number of moles
m = M \times
(ii) mass = molar mass × number of moles ⇒ m = M × n = 14 × 0.5 = 7 g
(iii) The number of moles, n = \frac{given\: number\: of\: particles}{Avogadro\: number}
n = \frac{N}{N_0}
n = \frac{3.011\times 10^{23}}{6.022\times 10^{23}}
14 ×0.5 = 7 g
(iv) n = \frac{N}{N_0}
m = M × n = M × \frac{N}{N_0}
m = 28 × \frac{6.022\times 10^{23}}{6.022\times 10^{23}}
m = 28 × 1 = 28 g
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