Practical: making and testing the smell of some esters in the lab
2 marks · EasyA student follows the laboratory method to prepare an ester using 2 cm³ of ethanol (density = 0.79 g/cm³) and 2 cm³ of ethanoic acid (density = 1.05 g/cm³). Calculate the total mass of reactants (ethanol and ethanoic acid) used, in grams. Give your answer to 2 decimal places.
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3.68 g (±0.01)
Also accept: 3.68
Common mistakes: adding the densities instead of multiplying by volume; using the wrong volume
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Marking points
M1 · 1 mark · Correctly calculates the mass of each reactant using mass = volume × density.
A1 · 1 mark · Adds both masses and gives the final answer to 2 decimal places (3.68 g). (follow-through)
Worked solution
Mass of ethanol = 2 cm³ × 0.79 g/cm³ = 1.58 g
Mass of ethanoic acid = 2 cm³ × 1.05 g/cm³ = 2.10 g
Total mass = 1.58 g + 2.10 g = 3.68 g (to 2 decimal places)