Concentrations of solutions
2 marks · HardA laboratory technician needs to prepare 400 cm³ of a potassium nitrate (KNO₃) solution with a concentration of 0.125 mol/dm³. Calculate the amount, in mol, of potassium nitrate required. Give your answer to 2 decimal places.
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0.05 mol (±0.01)
Also accept: 0.050 mol
Common mistakes: Not converting volume from cm³ to dm³; Incorrect multiplication
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Marking points
M1 · 1 mark · Correctly converts 400 cm³ to 0.400 dm³ and uses the formula amount = concentration × volume (in dm³).
A1 · 1 mark · Arrives at 0.05 mol with correct units (to 2 decimal places). (follow-through)
Worked solution
Volume in dm³ = 400 cm³ ÷ 1000 = 0.400 dm³