Volume Calculations

Copper(II) oxide and carbon react as shown:

Calculate the volume of carbon dioxide gas at room temperature and pressure that is produced from 24kg of CuO using excess carbon. Relative formula mass (Mr): Cu = 64, O = 16. Volume of 1 mole of any gas at room temperature and pressure is 24dm³.

[5 marks]

Visual Mark Scheme Breakdown

• What are the key values?

  • Potassium is at the top (very reactive)

  • Copper is at the bottom, below hydrogen

Copper(II) oxide and carbon react as shown:

Calculate the volume of carbon dioxide gas at room temperature and pressure that is produced from 24kg of CuO using excess carbon. Relative formula mass (Mr) of Cu = 64, O = 16. Volume of 1 mole of any gas at room temperature and pressure is 24dm³.

• Let's extract the values into our standard table. Do we need to convert any units? (1 mark)

  M (mass) should be in grams.

  For CuO, 24 kg should be converted:

  24 × 1000 = 24,000 g

  (1 mark)

• How do we find Mr of CuO? (1 mark)

  If Mr of Cu = 64 and O = 16, we simply add of one of each since there is one Cu and one O in CuO.

  64 + 16 = 80

  (1 mark)

• What can we now find for CuO? (1 mark)

  • We have M (mass) in g

  • We have Mr (relative formula mass)

  • We can find n (moles)

  n = M / Mr

  n = 24000 / 80 = 300 moles

  (1 mark)

• What can we now find using the ratio? (1 mark)

  We can find n (number of moles) for carbon dioxide:

  Ratio is 2:1

  If 2 represents 300 moles

  So 1 represents 150 moles

  (if we divide both sides by 2)

  (1 mark)

• Using the number of moles, how do we find volume of a gas? (1 mark)

  As mentioned in the question:

  1 mol of gas is 24 dm³

  So 150 mol of gas is 3600 dm³

  (If we multiply both sides by 150)

  (1 mark)

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