Reversing the calculations
3 marks · EasyPotassium hydroxide reacts with nitric acid according to the equation:
25.0 cm³ of 0.200 mol/dm³ potassium hydroxide solution is mixed with 25.0 cm³ of 0.200 mol/dm³ nitric acid.
Calculate the number of moles of potassium hydroxide in the mixture.
Calculate the number of moles of nitric acid in the mixture.
State the simplest whole-number ratio of reactant volumes needed for complete neutralisation according to the equation.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) 0.00500 mol
(b) 0.00500 mol
(c) 1 : 1
Common mistakes: Not converting volume to dm³; Using incorrect stoichiometric ratio
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Marking points
M1 (a) · 1 mark · Calculates moles of KOH using concentration × volume/1000 (0.200 × 25.0/1000)
M2 (b) · 1 mark · Calculates moles of HNO3 using concentration × volume/1000 (0.200 × 25.0/1000)
B1 (c) · 1 mark · States the correct simplest whole-number ratio is 1:1 as shown in the balanced equation.
Worked solution
a) Number of moles of KOH:
b) Number of moles of HNO₃:
c) The balanced equation shows a 1:1 ratio between KOH and HNO₃, so the ratio is 1:1.