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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