Edexcel A Level Chemistry Paper 3: General and Practical Principles in Chemistry June 2025 question paper 9CH0/03

This question is about ionisation energies.

The table shows the first four ionisation energies of three elements in the same group of the Periodic Table. The letters used are not the symbols of the elements.

State what is meant by the term ‘ first ionisation energy’.

Explain to which group the elements X, Y and Z belong.

Explain which of the elements X, Y and Z has the highest atomic number.

This question is about compounds that contain both an alkene and an alcohol functional group.

Describe a test, and the positive result, that confirms the presence of a

Test

Prop-2-en-1-ol can polymerise to form an addition polymer.

Write a balanced equation for this polymerisation.

Prop-2-en-1-ol can form the alkene propadiene, which has two adjacent

propadiene

Explain why the CH₂ groups at each end of the molecule are at right angles to each other. Use your knowledge of how orbitals overlap to form π-bonds.

The compound bombykol is a pheromone secreted by female silk moths. Like prop-2-en-1-ol, it can also be classified as both an alkene and an alcohol.

Bombykol can exist as a number of geometric isomers.

Give the number of different geometric isomers of bombykol.

Give the reason why prop-2-en-1-ol does not exhibit geometric isomerism.

Explain the expected solubilities in water of bombykol and prop-2-en-1-ol.

A student carries out a series of qualitative tests to identify the contents of three unlabelled bottles. The bottles are known to contain the following solutions.

• ammonium carbonate, (NH₄)₂CO₃(aq)

• potassium carbonate, K₂CO₃(aq)

• potassium sulfate, K₂SO₄(aq)

The student has access to just test tubes and a water bath, plus only the reagents shown.

AgNO₃(aq) BaCl₂(aq) Ca(OH)₂(aq) CuSO₄(aq)

HCl(aq) HNO₃(aq) MgCl₂(aq) NaOH(aq)

red litmus paper
blue litmus paper

The student carries out qualitative tests to positively identify either an anion or a cation in each compound and so identify the contents of each bottle.

Describe the qualitative tests carried out, the expected observations and appropriate deductions.

This question is about the kinetics of the reaction between iodine and propanone under acidic conditions. The equation for the reaction is shown.

An experiment is carried out to determine the order of the reaction with respect to iodine.

Step 1 50.0 cm³ of 0.0200 mol dm⁻³ iodine solution, I₂(aq), is added from a burette to a conical flask.

Step 2 25.0 cm³ of 2.00 mol dm⁻³ sulfuric acid, H₂SO₄(aq), is added to the conical flask using a pipette.

Step 3 25.0 cm³ of 2.00 mol dm⁻³ propanone solution, CH₃COCH₃(aq), is added to the conical flask using a pipette. The flask is swirled and a timer is started.

Step 4 After 2 minutes, a 10.0 cm³ sample of the reaction mixture is removed and quenched.

Step 5 The quenched sample is then titrated using 0.0100 mol dm⁻³ sodium thiosulfate solution, Na₂S₂O₃(aq).

Step 6 Steps 4 and 5 are repeated every two minutes, until six titres have been determined.

Before carrying out Step 2, a student noticed droplets of an unknown colourless aqueous solution in the pipette.

Describe how the pipette should be treated before it is used in Step 2. Justify your answer.

Samples from the reaction mixture are quenched in Step 4.

Explain why quenching is necessary.

State a compound which can be added to the reaction mixture to quench the reaction. Include an equation for the reaction that takes place during the quenching process. State symbols are not required.

Compound

Show, by calculating the initial quantities of the reactants involved, that this experiment provides evidence for the order with respect to iodine only.

The results of the experiment are shown.

Plot a graph of titre against time.

Give the reason why it is not necessary to calculate the concentration of iodine so that the order can be deduced.

Deduce the order with respect to iodine. Justify your answer.

This question is about cobalt complexes.

A sample of cobalt(II) chloride was dissolved in aqueous ammonia, NH₃(aq). During the process, a stream of oxygen was gently bubbled through the solution to oxidise the cobalt(II) ion.

A coloured solid, R, was extracted from the solution. A pure sample of this solid was found to contain the masses of the elements shown and had a molar mass of 233.4 g mol⁻¹.

Show that the empirical formula and the molecular formula of R is CoN₄H₁₂Cl₃. You must show your working.

1.00 g of R was dissolved in water forming a coloured solution of the complex ion, Q.

The solution was reacted with excess silver nitrate solution, forming 0.614 g of silver chloride, AgC l (s).

Calculate the number of moles of chloride ions released when 1 mol of R dissolves.

Draw the three-dimensional shape of the complex ion, Q, using your answer to (a)(ii) to help deduce the formula and overall charge.

An aqueous solution of cobalt(II) chloride contains the complex ion [Co(H₂O)₆]²⁺.

The dynamic equilibria shown occur when NH₃(aq) and EDTA⁴⁻(aq) are each added to separate solutions of this complex ion.

[Co(H₂O)₆]²⁺(aq) + 6NH₃(aq) [Co(NH₃)₆]²⁺(aq) + 6H₂O(l) log K_c = 4.39

[Co(H₂O)₆]²⁺(aq) + EDTA⁴⁻(aq) [Co(EDTA)]²⁻(aq) + 6H₂O(l) log K_c = 16.5

State what is meant by the term ‘dynamic equilibrium’.

Explain, in terms of equilibria and entropy, which of the three complex ions is the most stable.

The compound 2-methyl-1-phenylpropan-2-ol is found in small amounts in cocoa beans and has the structure shown.

A proposed synthesis of 2-methyl-1-phenylpropan-2-ol from phenylmethanol and propanone is shown.

Complete the diagram to show the structures of compounds A, B and C and the formula of reagent D.

2-Methyl-1-phenylpropan-2-ol can be converted to compound S. When considering the¹H NMR spectrum of S, the hydrogen atoms of the benzene have been assumed to be a single environment, labelled J. The other hydrogen environments have been labelled K, L, M and N.

Complete the table for each of the environments K to N in the high resolution ¹H NMR spectrum of S.

A laboratory technician analysed a sample of an alcoholic drink to determine the concentration of ethanol, in g dm⁻³.

20.00 cm³ of the alcoholic drink was added to a 250 cm³ volumetric flask and made up to the mark with deionised water.

The ethanol in 5.00 cm³ of the diluted sample was oxidised in the equipment shown.

The sample was suspended in an open beaker in a sealed conical flask over 10.00 cm³ of acidified sodium dichromate(VI), of concentration 0.0780 mol dm⁻³.

The apparatus was left in a warm place for 24 hours for the acidified sodium dichromate(VI) to oxidise the ethanol.

Excess potassium iodide solution was then added to the remaining acidified sodium dichromate(VI) in the conical flask, forming iodine.

All of this iodine was then titrated using 0.0220 mol dm⁻³ sodium thiosulfate solution, Na₂S₂O₃(aq).

The volume of Na₂S₂O₃(aq) required in the titration was 32.70 cm³.

The equations for the reactions that take place during the experiment are shown.

Explain why the apparatus was left in a warm room and for 24 hours.

Calculate the number of moles of ethanol in 5 cm³ of the diluted drink.

Calculate the concentration of ethanol in the alcoholic drink in g dm⁻³.

It was suggested that the titration as described might lead to an unreliable result.

State two ways the procedure could be amended to counter this suggestion.

Another technician suggested that it was unnecessary to suspend the drink sample above the acidified sodium dichromate(VI) solution and proposed a change to the procedure.

The proposal was that the drink sample should be mixed with the acidified sodium dichromate(VI) solution and then heated under reflux to allow the ethanol to be oxidised.

Give one reason to support this change and one reason to leave the method unchanged. In each case justify your answer.

Reason to support this change

Reason to leave the method unchanged

This question is about weak acids.

An aqueous solution of a weak acid, HA(aq), with a concentration of 0.0712 mol dm⁻³, has a pH = 3.25 at room temperature.

Calculate the value of K_a for the weak acid HA(aq).

The value of K_a may be determined from experimental data, using a titration curve.

Ethanoic acid, CH₃COOH(aq), with a concentration of 0.0500 mol dm⁻³, has a pH of 3.03 at room temperature.

A 20.0 cm³ sample of the acid was titrated with sodium hydroxide solution, NaOH(aq), with a concentration of 0.0500 mol dm⁻³. During the experiment, 40.0 cm³ of sodium hydroxide solution was slowly added to the ethanoic acid.

A pH probe connected to a data logger was used to monitor the pH throughout the experiment.

Calculate the pH of the sodium hydroxide solution. Give your answer to one decimal place.

[K_w = 1.0010⁻¹⁴mol²dm⁻⁶]

Draw a titration curve, on the axes shown, to show the change in pH throughout the experiment.

Give an estimate of the pH value at the half-equivalence point. Show your working on the titration curve.

Calculate a value for K_a of ethanoic acid using your answer to (b)(iii). You must show your working.

Another method used to monitor the titration is to use a pH meter without a data logger. The pH is measured and recorded after the addition of each 1.00 cm³ portion of NaOH(aq).

A student assessed the two methods and concluded that using the data logger was a more effective way to carry out the experiment.

Give three reasons that support this conclusion.

A solution containing propanoic acid and sodium propanoate forms a buffer.

2.30 g of sodium propanoate is dissolved in propanoic acid solution. This forms a buffer with pH = 4.2 and a volume of exactly 100 cm³.

Calculate the concentration of the propanoic acid, in mol dm^–3, in this buffer.

[K_a (propanoic acid) = 1.34×10⁻⁵mol dm⁻³ M_r(CH₃CH₂CO₂Na) = 96.0]

Explain why there is no significant change in pH when a small amount of hydrochloric acid, HC l (aq), is added to this buffer.

This question is about the compound 2,5-dimethylbenzenesulfonic acid, which has the structure shown.

It is used to analyse levels of cholesterol in blood plasma. It can be synthesised by the reaction of 1,4-dimethylbenzene with concentrated sulfuric acid. The electrophile in this reaction is sulfur trioxide.

Complete a possible mechanism for this reaction by adding curly arrows, and any relevant dipoles, charges and lone pairs.

The 2,5-dimethylbenzenesulfonic acid formed can be purified by recrystallisation using hot water as a solvent.

Procedure

Step 1 Dissolve impure 2,5-dimethylbenzenesulfonic acid in the minimum volume of hot water.

Step 2 Allow the solution to cool until 2,5-dimethylbenzenesulfonic acid has crystallised.

Step 3 Separate the 2,5-dimethylbenzenesulfonic acid by filtering under reduced pressure.

Step 4 Rinse the 2,5-dimethylbenzenesulfonic acid using a small amount of ice‑cold water.

Step 5 Dry the 2,5-dimethylbenzenesulfonic acid between two pieces of filter paper.

Explain how recrystallisation reduces the amount of soluble impurities.

A student carrying out this procedure noticed some insoluble impurities in their sample.

Describe how the procedure should be amended to remove these insoluble impurities.

The hydrated form of the acid has the formula C₆H₃(CH₃)₂SO₃H•nH₂O. An experiment was carried out to determine the number of moles of water of crystallisation, n, in this formula.

The method involves adding excess sodium hydroxide to a known mass of the hydrated 2,5-dimethylbenzenesulfonic acid. The amount of unreacted sodium hydroxide is then determined by titration.

Procedure

Step 1 10.0 cm³ of 1.00 mol dm⁻³ NaOH(aq) was added to 1.60 g of hydrated 2,5-dimethylbenzenesulfonic acid in a small conical flask.

Step 2 The solution formed was diluted to give a volume of exactly 100 cm³.

Step 3 20.0 cm³ samples of the diluted solution required a mean titre of 22.40 cm³ of 0.02500 mol dm⁻³ HCl(aq) to neutralise the unreacted sodium hydroxide present in the sample.

Describe how to make the diluted solution, in Step 2.

Calculate the relative formula mass of hydrated 2,5-dimethylbenzenesulfonic acid and hence deduce the value of n.

A student carrying out this experiment used a funnel as shown to try to ensure the acid was added safely to the burette during the titration.

Give one change to this technique that would reduce the risk to this student.

The student forgot to remove the funnel from the burette and during the titration five drops of acid from the funnel dripped into the burette.

Explain what effect, if any, this error will have on the final value for n.