AQA A-Level Chemistry AS Paper 1, June 2025: Question 9

1 mark · Medium difficulty · Multiple Choice

Calculate the mass, in kg, of 2000 m³ of carbon monoxide gas at 100 kPa and 25 °C using the ideal gas equation.

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Question

Question 09 asks: What is the mass, in kg, of 2000 m³ of carbon monoxide gas at 100 kPa and 25 °C? Given constant R = 8.31 J K⁻¹ mol⁻¹. Four multiple choice options are provided with selection lozenges: A: 2.261, B: 2.696, C: 2261, D: 2696. The question is worth 1 mark.
Question text

09 What is the mass, in kg, of 2000 m3 of carbon monoxide gas at 100 kPa and 25 °C?

R = 8.31 J K–1 mol–1

[1 mark]

A 2.261

B 2.696

C 2261

D 2696

Mark scheme

Show the mark scheme Mark scheme table showing question number 9 has correct answer C, awarded 1 mark (AO2), corresponding to the value 2261.

9 C 1 (AO2) 2261

How to answer it

Mass of Gas Using the Ideal Gas Equation

📌 What this question tests

This question assesses your ability to apply the Ideal Gas Equation (pV = nRT) to find the mass of a large volume of industrial gas under non-standard conditions. Specifically, it tests:

  • Rearranging pV = nRT to calculate the amount of substance in moles ( n ).
  • Performing essential SI unit conversions: pressure ( kPa to Pa ) and temperature ( °C to K ).
  • Recognising that volume given in m³ is already in standard SI units and does not need converting.
  • Calculating molar mass for carbon monoxide ( CO ) rather than carbon dioxide ( CO₂ ).
  • Converting calculated mass from grams ( g ) to kilograms ( kg ).

Question 09 Analysis

Multiple Choice (1 Mark) • AO2 Application of Knowledge

✅ Correct Answer

C — 2261

Awarded 1 mark for selecting option C.

💡 Key Knowledge

  • Ideal Gas Law: pV = nRT
  • SI Units required:
    • p in Pascals ( Pa ): 100 kPa = 100 000 Pa = 1.00 × 10⁵ Pa
    • V in cubic metres ( m³ ): already 2000 m³
    • T in Kelvin ( K ): 25 °C + 273 = 298 K
    • R = 8.31 J K⁻¹ mol⁻¹
  • Molar Mass ( Mr ): Carbon monoxide is CO : Mr = 12.0 + 16.0 = 28.0 g mol⁻¹ .

📐 Step-by-Step Calculation

  1. Convert all values to standard SI units:
    • Pressure, p = 100 kPa = 100 000 Pa
    • Volume, V = 2000 m³ (already in m³ )
    • Temperature, T = 25 + 273 = 298 K
  2. Rearrange pV = nRT to find moles ( n ):

    n = (p × V) / (R × T)

    n = (100 000 × 2000) / (8.31 × 298)

    n = 200 000 000 / 2476.38 = 80 763.05 mol

  3. Calculate mass in grams:

    mass (g) = n × Mr(CO)

    mass (g) = 80 763.05 mol × 28.0 g mol⁻¹ = 2 261 365 g

  4. Convert mass to kilograms ( kg ):

    mass (kg) = 2 261 365 / 1000 = 2261.37 kg ≈ 2261 kg

    Matches option C.

❌ Common Errors & Traps

  • The "Automatic" Volume Conversion Trap: In most lab-based exam questions, volume is given in cm³ or dm³ , requiring division by 10⁶ or 10³ . Here, volume is already in m³ ! Dividing by 1000 leads directly to Option A (2.261).
  • Incorrect Chemical Formula: Reading "carbon monoxide" quickly and calculating Mr for carbon dioxide ( CO₂ = 44.0 ) instead of CO ( 28.0 ).
  • Forgetting to Convert Temperature: Using 25 °C directly instead of adding 273 to give 298 K .
  • Unit Oversight at the End: Forgetting that mass = n × Mr yields grams, which must be divided by 1000 to obtain kilograms.

🧠 Exam Technique & Multiple Choice Strategy

  • Inspect the magnitude of options: Notice the options come in pairs: 2.261 vs 2261 , and 2.696 vs 2696 . The factor of 10³ indicates a unit conversion check (kg vs g or m³ vs dm³).
  • Sanity check the scale: 2000 m³ is an enormous volume (almost the size of an Olympic swimming pool). A gas at atmospheric pressure has a density around 1.1–1.2 kg m⁻³ . Therefore, 2000 m³ must have a mass of roughly 2000 × 1.1 ≈ 2200 kg . This instantly eliminates 2.261 kg as impossibly light!
  • Write unit tags alongside values: Always jot down Pa , m³ , and K next to your numbers to verify SI compliance before typing into the calculator.

Topics

Physical Chemistry · 3.1.2 Amount of Substance

Question and mark scheme from the AQA A-Level Chemistry examination, AS Paper 1, June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.