Calculate:
(a) the mass of 1.0505 × 1023 molecules of carbon dioxide (CO2).
(b) the number of molecules of 0.25 moles of NH3,
(c) the formula unit mass of Na2SO3.
[Atomic mass: Na = 23 u, S = 32 u, O = 16 u, H = 1 u, NA = 6.022 × 1023 mol–1]
(a) First we will convert 1.0505 × 1023 molecules of carbon dioxide (CO2) into number of moles:
We know, 1 mole = 6.022 × 1023(Na = Avogadro’s number)
Number of moles = 0.17
Now, to calculate mass, apply the formula:
We can write:
Mass(m) = Number of moles (n) × Molar mass of CO2 (M)
Mass = 0.17 mol × 44g/mol
Mass = 7.48g
Thus, the mass of 1.0505 × 1023 molecule of CO2 is 7.48g.
(b) Given: Number of moles = 0.25
We know, 1 mole = 6.022 × 1023(Na = Avogadro’s number)
We can write:
Number of molecules = Number of moles (n) × Na
Number of molecules = 0.25mol × 6.022 × 1023
Number of molecules = 1.5 × 1023
Thus, the number of molecules of 0.25 moles of NH3 is 1.5 × 1023
(c) Formula unit mass of Na2SO3 :
2 × Atomic mass of Na + Atomic mass of sulphur + 3 × Atomic mass of O
= 2 × 23 u + 32 u + 3 × 16 u
= 126 u
Thus, the formula unit mass of Na2SO3 is 126 u