You will determine the concentration of sulfuric acid by reaction with a known concentration of sodium hydroxide using a thermometric method. The equation for the reaction is shown. 2NaOH(aq) + H2SO4(aq) Na2SO4(aq) + 2H2O(l) FA 1 is 1.90 moldm-³ sodium hydroxide, NaOH. FA 2 is dilute sulfuric acid, H2SO4.

1. (a)Method • Place the cup in the 250 cm³ beaker. • Use the 25 cm³ measuring cylinder to transfer 25.0 cm³ of FA 1 into the cup. • Place the thermometer into the solution in the cup and record its temperature in the table of results. • Fill a burette with FA 2. • Run 5.00 cm³ of FA 2 into the solution in the cup. • Stir the mixture and record the highest temperature reached. • Repeat adding 5.00 cm³ volumes of FA 2 into the solution in the cup until 45.00cm³ has been added. Record the highest temperature reached after each addition. Results volume of FA 2 added/cm³ 0.00 | 5.00 | 10.00 | 15.00 | 20.00 temperature of solution/°C volume of FA 2 added/cm³ 25.00 | 30.00 | 35.00 | 40.00 | 45.00 temperature of solution/°C[3]
2. (b)(i)Plot a graph of temperature (y-axis) against volume of acid added (x-axis) on the grid provided. Select a scale on the y-axis to include a temperature 4.0°C above the highest temperature you recorded. Label any points you consider to be anomalous. Draw two lines of best fit, one for the rise in temperature and one for after the maximum temperature has been reached. Extrapolate the two lines so they intersect.[4]
3. (b)(ii)Use your graph to determine the volume of sulfuric acid, FA 2, required to neutralise 25.0 cm³ of sodium hydroxide, FA 1. volume of H2SO4 = ...................................... cm³[1]
4. (b)(iii)Calculate the concentration of sulfuric acid in FA 2. concentration of H2SO4 = ...................................... moldm-3[1]
5. (c)(i)State how the student used their graph to determine the value of ∆T for use in the equation q = mc∆T.[1]
6. (c)(ii)The student correctly calculated the value of ∆H for the reaction as ∆H = −55.2 kJ mol⁻¹. The theoretical value for ∆Hneut given in the student's textbook is –57.6 kJ mol⁻¹. Calculate the percentage error in the student's result compared with the theoretical value. percentage error = ...................................... %[1]
7. (c)(iii)Suggest why the student's result was less negative than the theoretical value. Explain your answer.[1]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.