Q. 205.0( 4 Votes )
Calculate:
(a) The number of moles of Sulphur (S8) present in 16 g of solid sulphur.
(b) the mass of 10 moles of sodium sulphite (Na2SO3).
(c) the number of atoms in 11.5 g of Na.
[atomic mass: Na = 23u; S = 32u, O = 16u, NA = 6.022 × 1023 mol–1]
Answer :
a) Given:
Mass of sulphur (m) = 16g
Atomic mass of sulphur (S8) = 8 × 32u = 256 u
Molar mass of S8 (M) = 256g/mol
To calculate the number of moles, we will apply the formula given below:
Number of moles = 0.0625
Thus, the number of moles in 16 g of solid sulphur is 0.0625.
b) Given:
Number of moles = 10
Molecular mass of sodium sulphite (Na2SO3) = 2 × Atomic mass of Na + atomic mass of sulphur + 3 × Atomic mass of O
= 2 × 23 u + 32 u + 48 u
= 126 u
Molar mass of Na2SO3 = 126g/mol
To calculate the mass, apply the formula:
We can write:
Mass = Number of moles × Molar mass
Mass = 10 mol × 126g/mol
Mass = 1260g
Thus, the mass of sodium sulphite is 1260g.
c) Given:
Mass of Na (m) = 11.5g
Atomic mass of sulphur = 23u
Molar mass of sulphur (M) = 23g/mol
To calculate the number of moles, we will apply the formula given below:
Number of moles = 0.5
We know, 1 mole = 6.022 × 1023(Na = Avogadro’s number)
We can write, number of atoms = Number of moles × Na
Number of atoms = 0.5 × 6.022 × 1023
Number of atoms = 3.022 × 1023
Thus, the number of atoms in 11.5 g of Na is 3.022 × 1023
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