CAIE A-Level Chemistry 2.2.1 The Mole

Practise defining amount of substance through the Avogadro constant and applying it to named particles.

Exam points

define one mole as containing the Avogadro constant of specified entities
name the entity clearly as atoms, molecules, ions, electrons or formula units
convert between moles and particles before applying any formula subscript multiplier

[Maximum number: 2]

Chlorine exists as a diatomic gas, $\mathrm{Cl}_{2}(\mathrm{~g})$ . A sample of $\mathrm{Cl}_{2}(\mathrm{~g})$ was made during a chemical reaction. When measured at 404 kPa and $25^{\circ} \mathrm{C}$ the sample occupied a volume of $20.0 \mathrm{~cm}^{3}$ .

Calculate the number of chlorine atoms in this sample of $\mathrm{Cl}_{2}(\mathrm{~g})$ . You may find it helpful to use your answer to (d)(i).

If you are unable to calculate an answer to (d)(i), use 0.36 g of $\mathrm{Cl}_{2}$ . This is not the correct answer.

number of chlorine atoms =

Method 1 & Method 2

$\mathbf{M} \mathbf{1}=3.263 \times 10^{-3} \times 2$ & $\mathbf{M} \mathbf{1}=\frac{0.23}{71.0} \times 2$ OR $6.53 \times 10^{-3}$ $\mathbf{M} \mathbf{2}=6.02 \times 10^{23} \times \mathbf{M} \mathbf{1}$ $=3.93 \times 10^{21}$ atoms of Cl

$\mathbf{M} \mathbf{2}=6.02 \times 10^{23} \times \mathbf{M} \mathbf{1}$ $=3.90 \times 10^{21}$ atoms of Cl

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2.2.1—Terms: mole question 1