Testing for carbonates (CO3^2-)
2 marks · EasyA student tests 0.20 g of sodium carbonate powder by adding excess dilute hydrochloric acid. Calculate the maximum volume of carbon dioxide gas produced at room temperature and pressure (RTP), assuming that 1 mole of gas occupies 24 dm^3 at RTP. (Relative formula mass of Na2CO3 = 106)
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0.045 dm^3 (±0.005)
Also accept: 0.0454 dm^3; 45 cm^3
Common mistakes: Incorrect use of relative formula mass; Incorrect volume calculation
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Marking points
M1 · 1 mark · Correctly calculates the number of moles of Na2CO3.
A1 · 1 mark · Uses stoichiometry and molar volume to calculate the correct volume of CO2 produced. (follow-through)
Worked solution
The equation for the reaction is:
Calculate moles of Na2CO3:
1 mole Na2CO3 produces 1 mole CO2, so moles of CO2 = 0.00189 mol.
Volume of CO2 = 0.00189 × 24 = 0.0453 dm^3.