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WAEC Chemistry 2021 Paper

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Question : 44

Total: 50

How many molecules of oxygen would occupy a volume of

2.24\,\mathrm{cm}^3

[Molar volume at s.t.p.

=22,400\,\mathrm{cm}^3

Avogadro's number

=6.02 \times 10^{23}

]

$3.01 \times 10^{20}$
$3.01 \times 10^{27}$
$6.02 \times 10^{19}$
$6.02 \times 10^{27}$

Solution:

Concept:

Convert the given volume into moles using the molar volume at s.t.p., then multiply by Avogadro's number to find the number of molecules.

Explanation:

Moles of oxygen

= \frac{\text{Volume}}{\text{Molar volume}}

= \frac{2.24\,\mathrm{cm}^3}{22400\,\mathrm{cm}^3}

= 1 \times 10^{-4}

moles

Number of molecules

= \text{Moles} \times \text{Avogadro's number}

= 1 \times 10^{-4} \times 6.02 \times 10^{23}

= 6.02 \times 10^{19}

molecules

Answer:

6.02 \times 10^{19}

molecules, i.e. option C.

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