All Questions: AS & A Level Chemistry - 9701 Paper 3 2011 Winter Zone 3
Theory
MCQ
01.
Theory 26 Marks
CH1 - ATOMS, MOLECULES & STOICHIOMETRY

You are to determine the enthalpy change of neutralisation of hydrochloric acid by aqueous sodium hydroxide and also the concentration of the aqueous sodium hydroxide. These can be found by measuring the temperature change when solutions of the acid and alkali are mixed.

FA 1 is aqueous sodium hydroxide, NaOH.
FA 2 is 2.00 mol dm-3 hydrochloric acid, HCl.

(a) Method

  • Fill a burette with FA 1. [Care: FA 1 is corrosive]
  • Support the plastic cup in a 250 cm3 beaker.
  • Use a measuring cylinder to transfer 25 cm3 of FA 2 into a 100 cm3 beaker.
  • Use a measuring cylinder to add 35 cm3 of distilled water to the acid in the beaker.
  • Measure and record, in the table below, the initial temperature of the mixture in the beaker.
  • Run 5.0 cm3 of FA 1 from the burette into the plastic cup.
  • Add the mixture of acid and water from the 100 cm3 beaker to the FA 1 in the plastic cup.
  • Stir carefully and measure the highest temperature obtained.
  • Record this temperature in the table.
  • Rinse the plastic cup with water.
  • Repeat the experiment using 25 cm3 of FA 2, 30 cm3 of distilled water and 10.0 cm3 of FA 1 as shown for experiment 2 in the table.
  • Carry out experiments 3 to 7 in the same way.
  • Complete the table for each experiment.

Results
experiment number1234567
volume of FA 2 / cm325252525252525
volume of water / cm33530252015105
volume of FA 1 / cm35.010.015.020.025.030.035.0
initial temperature of acidic mixture / °C
highest temperature / °C
temperature change / °C

(b) On the grid below plot the temperature change (y-axis) against the volume of FA 1 (x-axis). Using these points, draw two straight lines that intersect.

(c) Reading from the intersection of the two lines on your graph,
the volume of FA 1 is ............. cm3,
the temperature change is .......... °C. [1]
The volume of FA 1 at the intersection represents the volume of FA 1 which neutralised 25.0 cm3 of FA 2.
(d) The reaction between FA 1 and FA 2 is shown in the equation below.
NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)
This reaction is exothermic.
Use this information to explain the shape of the graph.
................................................................................................................
................................................................................................................
................................................................................................................
................................................................................................................ [2]
(e) Calculate the amount of heat energy produced in the reaction. Use the temperature change from (c) in calculating your answer.
[Assume that 4.3 J are required to raise the temperature of 1 cm3 of any solution by 1 °C]

heat energy produced = ..................... J [2]
(f) Calculate how many moles of hydrochloric acid are present in 25 cm3 of FA 2.

mol of hydrochloric acid = .................. [1]
(g) Use your answers to (e) and (f) to calculate the enthalpy change of neutralisation of hydrochloric acid by aqueous sodium hydroxide.

Give your answer in kJ mol-1 and include the relevant sign.

enthalpy change of neutralisation = ............. .................. kJ mol-1 [2]
(h) Explain why the total volume of solution used was kept constant in each of the experiments.
................................................................................................................
................................................................................................................
................................................................................................................ [1]
(i) Calculate the concentration, in mol dm-3, of the aqueous sodium hydroxide, FA 1.

concentration of FA 1 = .................. mol dm-3 [2]
(j) A student thought that the experiment was not accurate because the temperature changes measured were small.
Suggest a modification to the experimental method used in order to give larger changes in temperature.
................................................................................................................
................................................................................................................
................................................................................................................ [1]
(k) Experiments 1 to 7 were repeated using 1.00 mol dm-3 sulfuric acid, H2SO4, instead of the 2.00 mol dm-3 hydrochloric acid, HCl.
On the axes below indicate an appropriate temperature scale and sketch the graph for the temperature changes you would expect.


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02.
Theory 15 Marks
CH1 - ATOMS, MOLECULES & STOICHIOMETRY

(a) You are provided with three sodium salts FA 3, FA 4 and FA 5. Each salt contains one of the ions carbonate, $CO_3^{2-}$, sulfite, $SO_3^{2-}$ or sulfate, $SO_4^{2-}$.

(i) Using your knowledge of the reactions of these ions, suggest one reagent you could add to the solid to find out which ion is present in each of the solids.
..................................................................................................................................

(ii) Use the reagent you selected in (i) to identify which of these ions is present in FA 3, FA 4 and FA 5.
Carry out suitable tests on a small amount of each solid and record the results of your experiments in an appropriate form in the space below.

Identify the anions in FA 3, FA 4 and FA 5.
FA 3 contains the ....................... ion.
FA 4 contains the ....................... ion.
FA 5 contains the ....................... ion.

(b) (i) You are provided with FA 6 both as a solid and in aqueous solution. Complete the following table.

[Table_1]

testobservations
To a small spatula measure of FA 4 in a test-tube, add enough distilled water to make a solution.
Add 1 cm depth of FA 6 solution.
To a small spatula measure of FA 5 in a test-tube, add enough distilled water to make a solution.
Add 1 cm depth of FA 6 solution.
To 1 cm depth of FA 6 solution in a test-tube, add aqueous sodium hydroxide.
Carefully heat the solid FA 6 in the test-tube provided.
Note: two gases are released.

[6]

(ii) From the results of the tests in (i), identify the cation present in FA 6.
Cation present in FA 6 is ..........................
[1]

(iii) Suggest and use another reagent to confirm the cation present in FA 6.
reagent .........................................................................................................................
observation...................................................................................................................
[2]

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