When heated, a sample of potassium chlorate(V) (KClO₃) produced 67.2 cm³ of oxygen, measured at 298 K and 110 kPa - AQA - A-Level Chemistry - Question 7 - 2020 - Paper 3

To calculate the number of moles of oxygen produced, we can use the ideal gas law formula:

$PV = nRT$

Where:

• P = pressure in pascals = 110 kPa = 110,000 Pa
• V = volume in cubic meters = 67.2 cm³ = 67.2 × 10^{-6} m³
• n = number of moles of gas
• R = gas constant = 8.31 J K⁻¹ mol⁻¹
• T = temperature in kelvin = 298 K

Substituting in the known values:

$n = \frac{PV}{RT} = \frac{(110000 \, \text{Pa}) \times (67.2 \times 10^{-6} \, \text{m}^3)}{(8.31 \, \text{J K}^{-1} \text{mol}^{-1}) \times (298 \, \text{K})}$

Calculating this gives:

$n \approx 2.73 \times 10^{-3} \text{ moles of } O_2$