Question 5
18 g of glucose is made up to 250 cm³ of solution. What is the concentration? (molar mass 180 g mol⁻¹)
The right answer is the one marked above.
0.4 mol dm-3. 18 g ÷ 180 g mol⁻¹ = 0.1 mol in 250 cm³, and 250 cm³ is a quarter of a cubic decimetre, so 1 dm³ would hold 0.4 mol.
0.1 is the amount in moles, not the concentration — the volume conversion is the step that is easiest to skip. A concentration in mol dm⁻³ always needs the volume expressed in dm³.