Question

Atomic mass of some elements are given [Mg=24,O=16]... (a) How many atoms are there in 120g Mg? (b)Find the mass of 4X6.022X10²³ oxygen atoms
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Answer 1

Answer:-

(a) 3.011×10²⁴ atoms

(b) 64g

Explanation :-

Number 'a':-

• Atomic mass of Magnesium (Mg) = 24u

Thus, molar mass is 24g/mol.

Number of moles in 120g of Mg :-

= Given Mass/Molar mass

= 120/24

= 5 moles

Number of atoms :-

= No of moles × Avogadro Number

= 5×6.022×10²³

= 30.11×10²³

= 3.011×10²⁴ atoms

Number 'b' :-

• Atomic mass of Oxygen = 16u

Thus, molar mass is 16g/mol.

Number of moles in 4×6.022×10²³ atoms

of oxygen :-

= No of atoms/Avogadro Number

= 4×6.022×10²³/6.022×10²³

= 4 moles

=> Mass = No of moles × Molar mass

=> Mass = 4×16

=> Mass = 64g