The ideal gas equationAQA A-Level Chemistry: Subtopic test

1. 1
   A sample of nitrogen gas is held in a rigid flask of volume 250 cm³. The gas is at a temperature of 27 °C and a pressure of 120 kPa.

   (a)

   What is the volume of the flask in m³?

   [1 mark]

   • A2.50 × 10⁻⁷ m³
   • B2.50 × 10⁻⁴ m³
   • C2.50 × 10⁻² m³
   • D2.50 × 10² m³

   (b)

   What is the temperature of the nitrogen in the units needed for the ideal gas equation?

   [1 mark]

   • A27 K
   • B246 K
   • C327 K
   • D300 K

   (c)

   Calculate the amount, in mol, of nitrogen in the flask. The gas constant, R = 8.31 J K⁻¹ mol⁻¹.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A sealed, rigid steel cylinder of fixed volume contains helium used to fill party balloons. The cylinder is stored in a warehouse where the temperature changes between night and day.

   (a)

   Which expression gives the amount of helium, n, in the cylinder in terms of its pressure, volume and temperature?

   [1 mark]

   • An = pV/RT
   • Bn = RT/pV
   • Cn = pVRT
   • Dn = pT/RV

   (b)

   The cylinder is moved from a store at 280 K to a hot room at 560 K. What happens to the pressure of the gas, assuming none escapes?

   [1 mark]

   • AIt halves
   • BIt stays the same
   • CIt doubles
   • DIt quadruples

   (c)

   Use the ideal gas equation to explain why the pressure in the cylinder is higher on a hot day than at night.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student determines the relative molecular mass of a volatile liquid. She injects 0.223 g of the liquid into a gas syringe held in an oven at 100 °C. The liquid vaporises completely and the vapour occupies 95.0 cm³ at a pressure of 101 kPa. The gas constant, R = 8.31 J K⁻¹ mol⁻¹.

   (a)

   Calculate the amount, in mol, of vapour in the gas syringe.

   [3 marks]

   (b)

   Calculate the relative molecular mass of the liquid. Use your answer to (a) to deduce which of these liquids it is: propanone (Mr 58.0), pentane (Mr 72.0) or hexane (Mr 86.0).

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A sodium azide airbag generator decomposes according to 2NaN₃ → 2Na + 3N₂. The nitrogen produced must fill a 40.0 dm³ airbag at a temperature of 300 K and a pressure of 105 kPa. In a separate test, the nitrogen from the generator is released into a rigid 25.0 dm³ test tank at 350 K. The gas constant, R = 8.31 J K⁻¹ mol⁻¹, and the relative formula mass of NaN₃ is 65.0.

   (a)

   Calculate the minimum mass of sodium azide needed to inflate the airbag to 40.0 dm³ at 300 K and 105 kPa.

   [6 marks]

   (b)

   A technician calculates the pressure in the test tank when 1.68 mol of nitrogen at 350 K fills it, writing p = (1.68 × 8.31 × 350) / 25.0 = 195 Pa. Evaluate this calculation. Your answer should include the correct pressure, and a conclusion about whether a tank rated to withstand 150 kPa is safe to use.

   [6 marks]

   Total for question 4: 12 marks

End of questions