CAIE A-Level Physics 15.1 The Mole

Practise using the mole and Avogadro constant to convert between amount of substance, particle number and molar quantities.

Exam points

use the mole and Avogadro constant to calculate amount of substance, particle number and molar quantities

Covered syllabus points

15.1.1—Amount of substance is an SI base quantity with the base unit mol 15.1.2—Molar quantities where one mole of any substance is the amount containing a

[Maximum number: 3]

A fixed mass of an ideal gas has volume $210 \mathrm{~cm}^{3}$ at pressure $3.0 \times 10^{5} \mathrm{~Pa}$ and temperature 270 K . The volume of the gas is reduced at constant pressure to $140 \mathrm{~cm}^{3}$ , as shown in Fig. 2.1.

Fig. 2.1

The final temperature of the gas is T.

Determine:

the amount of gas
amount = mol

p V=n R T

C1

$n=\left(3.0 \times 10^{5} \times 210 \times 10^{-6}\right) /(8.31 \times 270)$

C1

$=0.028 \mathrm{~mol}$

A1

[Maximum number: 1]

A sealed vessel contains a mass of 0.0424 kg of an ideal gas at $227^{\circ} \mathrm{C}$ . The pressure of the gas is $1.37 \times 10^{5} \mathrm{~Pa}$ and the volume of the gas is $0.640 \mathrm{~m}^{3}$ .

Calculate:

the mass of one molecule of the gas

mass =kg [1]

mass $=0.0424 /\left(1.27 \times 10^{25}\right)$ $=3.34 \times 10^{-27} \mathrm{~kg}$

A1

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Covered syllabus points

15.1 The mole question 1

15.1 The mole question 2