Question

Calculate :
The mass of 1.0505 * 10²³ molecule of carbon dioxide ?
the no. of molecule of 0.25 mole of NH₃ ?
The formulae unit mass of Na₂ SO₃ .

Answer 1

a)
Molar mass of CO₂ = 44 g/mol
$6.022\times {10}^{23}$ molecules = 1 mole

Therefore, 1.0505 $\times$ 10²³ molecules = $\frac{1.0505\times {10}^{23}}{6.022\times {10}^{23}}=0.1744\mathrm{moles}$

Mass of one mole of CO₂ = 44 g
Therefore, mass of 0.1744 moles = 44 $\times$ 0.1744 g = 7.67 g

b)
No of molecules in one mole of NH₃ = ​$6.022\times {10}^{23}$
Therefore, no of molecules in 0.25 moles = 1.5055 ​$\times$ 10²³ molecules

c)
The formula unit mass of Na₂SO₃ = 23 x 2 + 32 + 16 x 3
= 46 + 32 + 48
= 126 u