Reversing the calculations
3 marks · NormalExplain, using a calculation, how you would work out the volume of 0.250 mol/dm³ potassium hydroxide solution needed to neutralise 10.0 cm³ of 0.500 mol/dm³ sulfuric acid, given the following equation:
Show your reasoning and working clearly.
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Calculate moles of H2SO4, use stoichiometric ratio to determine moles KOH needed, then use concentration of KOH to calculate the required volume.
Common mistakes: missing conversion to cm³; not applying stoichiometric ratio
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Marking points
M1 · 1 mark · Calculates moles of H2SO4 from given volume and concentration.
M2 · 1 mark · Uses the 2:1 mole ratio to determine moles of KOH needed. (follow-through)
M3 · 1 mark · Accurately calculates the volume of KOH solution required, showing correct working and reasoning. (follow-through)
Worked solution
1. Find moles of H2SO4:
2. Equation shows 2 mol KOH reacts with 1 mol H2SO4, so moles of KOH required = 2 × 0.00500 = 0.0100 mol.
3. Calculate the volume of KOH solution needed: