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(a) Method
**Dilution**
Pipette 25.0 $\text{cm}^3$ of FA 1 into the 250 $\text{cm}^3$ graduated (volumetric) flask labelled FA 3.
Make the solution up to the mark using distilled water.
Shake the flask to mix the solution of FA 3.
**Titration**
Rinse out the pipette with distilled water and then with FA 3.
Pipette 25.0 $\text{cm}^3$ of FA 3 into a conical flask.
Add 5 drops of phenolphthalein indicator to the flask. The indicator should remain colourless.
Fill the burette with FA 2.
Titrate FA 3 with FA 2, until a permanent pale pink colour is obtained.
You should perform a rough titration.
In the space below record your burette readings for this rough titration.
The rough titre is ............ $\text{cm}^3$.
Carry out as many accurate titrations as you think necessary to obtain consistent results.
Record in a suitable form below all of your burette readings and the volume of FA 2 added in each accurate titration.
Make sure that your recorded results show the precision of your practical work.
(b) From your accurate titration results, obtain a suitable value to be used in your calculations.
Show clearly how you have obtained this value.
25.0 $\text{cm}^3$ of FA 3 required ................. $\text{cm}^3$ of FA 2.
(c) Calculations
Show your working and appropriate significant figures in the final answer to each step of your calculations.
(i) Calculate how many moles of NaOH were present in the volume of FA 2 calculated in (b).
............... mol of NaOH
(ii) Calculate how many moles of $\text{H}_2\text{SO}_4$ were present in 25.0 $\text{cm}^3$ of FA 3.
$$\text{H}_2\text{SO}_4(\text{aq}) + 2\text{NaOH}(\text{aq}) \rightarrow \text{Na}_2\text{SO}_4(\text{aq}) + 2\text{H}_2\text{O}(l)$$
............... mol of $\text{H}_2\text{SO}_4$
(iii) Calculate how many moles of $\text{H}_2\text{SO}_4$ were present in 25.0 $\text{cm}^3$ of the undiluted solution FA 1.
............... mol of $\text{H}_2\text{SO}_4$
(iv) Calculate the concentration, in mol $\text{dm}^{-3}$, of $\text{H}_2\text{SO}_4$ in FA 1.
The concentration of $\text{H}_2\text{SO}_4$ in FA 1 was ............. mol $\text{dm}^{-3}$.
502
504
544
You will determine, using Hess' Law, the enthalpy change, $\Delta H_1$, for the reaction of magnesium with oxygen to form magnesium oxide.
$$\mathrm{Mg(s) + \frac{1}{2}O_2(g) \rightarrow MgO(s)}$$
(a) Reaction of magnesium with sulfuric acid
Method
FA 4 is 0.64 mol dm$^{-3}$ sulfuric acid.
FA 5 is magnesium turnings. This is supplied in two containers.
You will carry out the experiment twice.
• Support the plastic cup in a 250 cm3 beaker.
• Using a measuring cylinder, transfer 25 cm3 of FA 4 into the plastic cup.
• Tilt the beaker so that the bulb of the thermometer is covered by the solution. Measure and record the initial temperature of the solution.
• Carefully, add all the FA 5 from one of the containers into the plastic cup.
• Stir the mixture constantly with the thermometer.
• Record the highest temperature obtained.
• Empty and rinse the plastic cup and dry it with a paper towel.
• Repeat the experiment using the second portion of FA 5.
In the space below, record all your readings in an appropriate form. Calculate the mean temperature rise.
mean temperature rise = ...................... °C [5]
Calculation
Show your working and express your answers to three significant figures.
(i) Using the mean temperature rise above, calculate the mean heat energy produced in the reaction. (You may assume that 4.3 J are required to raise the temperature of 1.0 cm3 of any solution by 1.0 °C.)
heat energy produced = ...................... ............
value unit
(ii) Calculate the enthalpy change, $\Delta H_2$, in kJ mol$^{-1}$, for the following reaction.
$$\mathrm{Mg(s) + H_2SO_4(aq) \rightarrow MgSO_4(aq) + H_2(g)}$$
You should assume that the magnesium in your reaction is in excess.
$\Delta H_2$ = .......... ...................... kJ mol$^{-1}$ [2]
(b) Reaction of magnesium oxide with sulfuric acid
Method
FA 4 is 0.64 mol dm$^{-3}$ sulfuric acid.
FA 6 is magnesium oxide.
• Using a measuring cylinder, transfer 50 cm3 of FA 4 into a 250 cm3 beaker.
• Place the beaker on a tripod and gauze, and heat gently until the temperature of the acid reaches 45°C–60°C.
• Support a plastic cup in a 250 cm3 beaker.
• Transfer all the solution of hot FA 4 into the plastic cup.
• Stir and record the temperature of hot FA 4.
• Immediately add all the FA 6 to the FA 4 in the plastic cup.
• Stir the mixture constantly with the thermometer.
• Record the highest temperature obtained.
In the space below, record all your readings in an appropriate form. [3]
Calculation
Show your working and express your answers to three significant figures.
(i) Calculate the heat energy produced in the reaction. (You may assume that 4.3 J are required to raise the temperature of 1.0 cm3 of any solution by 1.0 °C.)
heat energy produced = ...................... ............
value unit
(ii) Calculate the enthalpy change, $\Delta H_3$, in kJ mol$^{-1}$, for the following reaction.
$$\mathrm{MgO(s) + H_2SO_4(aq) \rightarrow MgSO_4(aq) + H_2O(l)}$$
You should assume that the magnesium oxide in your reaction is in excess.
$\Delta H_3$ = .......... ...................... kJ mol$^{-1}$ [3]
(iii) The enthalpy change for the following reaction is –286 kJ mol−1.
$$\mathrm{H_2(g) + \frac{1}{2}O_2(g) \rightarrow H_2O(l)}$$ $\Delta H = -286$ kJ mol−1
Use the Hess' Law cycle given below to calculate $\Delta H_1$, the enthalpy change for the reaction of magnesium with oxygen.
(c) Suggest one improvement to the method by which heat losses from your apparatus could have been reduced.
..............................................................................................
.............................................................................................. [1]
521
508
511
(a) FA 7 contains one cation and one anion from those listed in the Qualitative Analysis Notes on pages 10 and 11.
Put two spatula measures of FA 7 into a test-tube. Add about two-thirds of a test-tube of distilled water and dissolve the solid. For each test that you carry out, use 1 cm depth of the solution of FA 7.
(i) Carry out the following tests and complete the table below.
[Table]
Add 5 drops of aqueous barium chloride (or barium nitrate) to your solution of FA 7.
Add 5 drops of aqueous silver nitrate to your solution of FA 7.
(ii) Put a very small spatula measure of solid FA 7 into a hard glass test-tube. Hold the test-tube horizontally and heat it gently for a few seconds, then heat it strongly until no further change takes place. Leave the test-tube to cool to room temperature. While cooling takes place, move on to (iv). In the space below record the observations made at each stage in an appropriate form.
(iii) State what deductions you can make about the identity of the anion in FA 7 from the tests above.
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(iv) Use the information in the Qualitative Analysis Notes on pages 10 and 11 to select a further test to confirm the identity of the anion in FA 7.
test .....................................................................................................
Carry out this test and, in the space below, record the observation(s) made in an appropriate form. State your conclusion.
(v) The cation in FA 7 is aluminium ion, calcium ion or zinc ion. Select one reagent to identify the cation in FA 7.
reagent ............................................................................................
Use this reagent to carry out a test. Record the observation(s) made and identify the cation.
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(b) FA 8 contains one cation from those listed on page 10 and 11.
Put all of the FA 8 into a test-tube.
Half fill the test-tube with distilled water and dissolve the solid.
(i) To 1 cm depth of the solution of FA 8 in a test-tube, add aqueous potassium iodide until the test-tube is half full. Allow the mixture to stand for two minutes. Use a dropping pipette to transfer about 1 cm3 of the mixture from the top of the test-tube to another test-tube. Add 5 drops of starch solution. Record all of your observations.
(ii) State what type of chemical behaviour has been shown by potassium iodide in this reaction. Give an ionic equation to justify your answer.
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(iii) To another 1 cm depth of solution of FA 8 in a test-tube, add aqueous sodium hydroxide. Record the observation(s) made. Give the ionic equation for the reaction taking place.
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571
510
555
