Question

Calculate :

(a) The number of moles of sulphur (S8)present in 16g of solid

sulphur.

(b)The mass of 10 moles of sodium sulphite(Na2SO3)

(c)The number of atoms in 11.5 g of Na atom.

( atomic mass:Na= 23u, S=32u, O= 16u,

Avogadro number= 6.022x 1023)






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Answer 1

Explanation:

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 = Givenmass(m)Molarmass(M)Givenmass(m)Molarmass(M)

Number of moles = 16g256g/mol16g256g/mol

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:

Number of moles = Mass(m)Molarmass(M)Mass(m)Molarmass(M)

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 = Givenmass(m)Molarmass(M)Givenmass(m)Molarmass(M)

Number of moles = 11.5g23g/mol11.5g23g/mol Number of moles = 0.5 We know, 1 mole = 6.022 x 1023(Na = Avogadro's number)

The number of moles = NumberofatomsAvogadro′snumberNumberofatoms

Avogadro′snumber We can write, number of atoms

= Number of moles × Na Number of atoms

= 0.5 × 6.022 × 1023 Number of atoms = 3.022 × 10^23

Thus, the number of atoms in 11.5 g of Na is 3.022 X10^23