Chemical Formulae, Equations and Calculations Part 1
2 marks · EasyCalculate the number of moles in 12.0 g of magnesium oxide, MgO. (Ar: Mg = 24, O = 16)
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0.30 mol (±0.01)
Must show: Calculation of Mr (40), Use of moles = mass/Mr (12.0/40 = 0.30)
Common mistakes: Does not calculate Mr; Incorrect calculation
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Marking points
M1 · 1 mark · Calculates Mr of MgO as 40.
A1 · 1 mark · Calculates moles as 12.0 / 40 = 0.30 mol.
Worked solution
Mr(MgO) = 24 + 16 = 40.
Moles = 12.0 / 40 = 0.30 mol.