1. 1
   A student titrates 25.0 cm3 of sodium hydroxide solution of known concentration 0.100 mol/dm3 against an unknown concentration of hydrochloric acid, using the reaction HCl + NaOH -> NaCl + H2O. The mean titre of acid needed to exactly neutralise the alkali is 22.5 cm3.

   (a)

   What is the mole ratio of hydrochloric acid to sodium hydroxide in this equation?

   [1 mark]

   • A1 : 1
   • B1 : 2
   • C2 : 1
   • D1 : 3

   (b)

   What is the mean titre of 22.5 cm3 expressed in dm3?

   [1 mark]

   • A0.0225 dm3
   • B0.225 dm3
   • C2.25 dm3
   • D22.5 dm3

   (c)

   Calculate the number of moles of sodium hydroxide used in this titration, showing your working.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A different student titrates 20.0 cm3 of potassium hydroxide solution of known concentration 0.200 mol/dm3 against an unknown concentration of sulfuric acid, using the reaction H2SO4 + 2KOH -> K2SO4 + 2H2O. The mean titre of acid needed to exactly neutralise the alkali is 16.0 cm3.

   (a)

   What is the mole ratio of sulfuric acid to potassium hydroxide in this equation?

   [1 mark]

   • A1 : 2
   • B1 : 1
   • C2 : 1
   • D1 : 3

   (b)

   How many moles of potassium hydroxide were used in this titration?

   [1 mark]

   • A0.004 mol
   • B0.002 mol
   • C0.02 mol
   • D0.0016 mol

   (c)

   Using the mole ratio for this reaction, calculate the number of moles of sulfuric acid present in the 16.0 cm3 titre, showing your working.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student titrates 25.0 cm3 of sodium hydroxide solution of known concentration 0.150 mol/dm3 against an unknown concentration of nitric acid, using the reaction HNO3 + NaOH -> NaNO3 + H2O. The mean titre of acid needed to exactly neutralise the alkali is 20.0 cm3. (Mr of HNO3 = 63)

   (a)

   Calculate the concentration of the nitric acid in mol/dm3, showing your working, giving your answer to 3 significant figures.

   [3 marks]

   (b)

   Using your answer to part (a), calculate the concentration of the nitric acid in g/dm3, showing your working. (Mr of HNO3 = 63)

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A water-testing laboratory is checking two industrial samples for acid contamination. The first is suspected to contain nitric acid; it is titrated against 25.0 cm3 of 0.200 mol/dm3 sodium hydroxide, with a mean titre of 18.0 cm3 of run-off needed. The second is suspected to contain sulfuric acid; it is titrated against 20.0 cm3 of 0.250 mol/dm3 potassium hydroxide, with a mean titre of 15.0 cm3 of run-off needed.

   (a)

   A water-testing laboratory suspects that a sample of industrial run-off contains dissolved nitric acid. To check, 25.0 cm3 of sodium hydroxide solution of known concentration 0.200 mol/dm3 is titrated against the run-off sample, using the reaction HNO3 + NaOH -> NaNO3 + H2O. The mean titre of run-off needed is 18.0 cm3. Calculate the concentration of nitric acid in the run-off sample, in both mol/dm3 and g/dm3, showing full working. (Mr of HNO3 = 63)

   [6 marks]

   (b)

   The second industrial sample is suspected to contain sulfuric acid. 20.0 cm3 of potassium hydroxide solution of known concentration 0.250 mol/dm3 is titrated against this sample, using the reaction H2SO4 + 2KOH -> K2SO4 + 2H2O. The mean titre of run-off needed is 15.0 cm3. Calculate the concentration of sulfuric acid in the run-off sample, in both mol/dm3 and g/dm3, showing full working. (Mr of H2SO4 = 98)

   [6 marks]

   Total for question 4: 12 marks

End of questions