Gas volumes and the ideal gas equationEdexcel International A Level Chemistry: Subtopic test

1. 1
   A student reacts 0.120 g of magnesium ribbon with an excess of dilute hydrochloric acid and collects the hydrogen in a gas syringe at room temperature and pressure (rtp). The molar volume of a gas at rtp is 24.0 dm³ mol⁻¹. The relative atomic mass of magnesium is 24.3.

   (a)

   What volume of hydrogen should the student collect?

   [1 mark]

   • A119 cm³
   • B237 cm³
   • C59.3 cm³
   • D0.119 cm³

   (b)

   Why does the student use an excess of hydrochloric acid?

   [1 mark]

   • ATo increase the volume of hydrogen produced
   • BTo ensure all the magnesium reacts, so the volume depends only on the mass of magnesium
   • CTo act as a catalyst for the reaction
   • DTo keep the temperature of the mixture constant

   (c)

   The student collects only 108 cm³ of hydrogen. Suggest two reasons why the measured volume is less than the calculated volume.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A gas cylinder of fixed volume 2.50 dm³ contains 4.00 g of methane, CH₄ (molar mass 16.0 g mol⁻¹), at 300 K. Take R = 8.31 J K⁻¹ mol⁻¹ and the molar volume at rtp as 24.0 dm³ mol⁻¹.

   (a)

   What is the pressure of the methane in the cylinder?

   [1 mark]

   • A2.24 × 10⁴ Pa
   • B2.49 × 10² Pa
   • C2.49 × 10⁵ Pa
   • D2.49 × 10⁸ Pa

   (b)

   The cylinder is cooled to 280 K at constant volume. What is the new pressure?

   [1 mark]

   • A2.67 × 10⁵ Pa
   • B2.49 × 10⁵ Pa
   • C2.33 × 10² Pa
   • D2.33 × 10⁵ Pa

   (c)

   Calculate the volume the methane would occupy at rtp and use this to state whether the gas in the cylinder is at a higher or lower pressure than atmospheric pressure.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A volatile liquid X is one of propanone (C₃H₆O), diethyl ether (C₄H₁₀O) or hexane (C₆H₁₄). A sample of mass 0.205 g is vaporised completely in a gas syringe and occupies 85.0 cm³ at 373 K and a pressure of 101 kPa. Take R = 8.31 J K⁻¹ mol⁻¹. Relative atomic masses: H = 1.0, C = 12.0, O = 16.0.

   (a)

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

   [3 marks]

   (b)

   Calculate the molar mass of X and use it to deduce the identity of X.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A camping-stove cartridge of internal volume 450 cm³ contains 220 g of liquefied propane, C₃H₈ (molar mass 44.0 g mol⁻¹). Propane burns in air according to C₃H₈(g) + 5O₂(g) → 3CO₂(g) + 4H₂O(l). Take the molar volume at rtp as 24.0 dm³ mol⁻¹, R = 8.31 J K⁻¹ mol⁻¹, and air as 20% oxygen by volume.

   (a)

   A stove burns 2.20 g of propane completely at rtp. Calculate the volume of oxygen needed, the volume of carbon dioxide formed, and the volume of air needed. Give your answers in dm³.

   [6 marks]

   (b)

   Suppose all of the propane in the cartridge were a gas at 293 K. Calculate the pressure it would exert, and explain why the real pressure inside a cartridge is much lower than your answer.

   [6 marks]

   Total for question 4: 12 marks

End of questions