Chemistry · Edexcel 9CH0 · Paper 3: General and Practical Principles in Chemistry · June 2024
Relative isotopic mass is an important concept in chemistry.
Define relative isotopic mass.
(2)
A sample of hydrogen gas is formed from atoms of three isotopes,1H,2H and3H.
Deduce the number of peaks due to molecular ions, H2+, in the mass spectrum of this sample.
(1)
This question is about the intermolecular forces in organic compounds.
The structures of four isomeric alkanes are shown.
compound A
compound B
compound C compound D
The only significant intermolecular forces between molecules of these compounds are London forces.
Explain how London forces arise.
(3)
Explain which of the compounds A – D will have the highest boiling temperature.
(2)
The apparatus shown may be used in an experiment to compare how far, if at all, a charged rod deflects different liquids.
The structures of three liquids are shown.
Explain whether or not each of these liquids will be deflected in this experiment.
(3)
Give a reason, with reference to the filtration in Step 3, why the formation of extremely small crystals in Step 2 would lead to a lower mass of dry barium sulfate in Step 5.
(1)
Explain why the crystals are rinsed in Step 4.
(2)
Calculate the relative formula mass of M2SO4 and hence identify M.
[Mr of BaSO4 = 233.4]
(3)
Another student carrying out the experiment placed the glass rod on the laboratory bench when the stirring was complete in Step 1.
Explain what effect this would have on the calculated value of the relative formula mass of M2SO4.
(2)
Describe how the student should amend the procedure.
(1)
Another way to identify a metal ion is a flame test.
Explain what causes the flame colour in such a test.
(2)
Give one advantage and one disadvantage of using a flame test to identify a metal cation, rather than the method followed by the students in Steps 1 – 5.
(2)
This question is about the white crystalline solid, barium nitrate.
Barium nitrate decomposes under suitable conditions to form barium oxide, nitrogen dioxide and oxygen.
Standard molar entropy data related to this reaction are shown.
| Substance | Standard molar entropy, S  / J K–1mol–1 |
| Ba(NO3)2(s) | 213.8 |
| BaO(s) | 70.4 |
| NO2(g) | 240.0 |
| O2(g) | 205.0 |
Show that barium nitrate is thermally stable at 298 K.
(5)
Calculate the minimum temperature, in °C, at which it is thermodynamically feasible for barium nitrate to decompose.
Give your answer to an appropriate number of significant figures.
(3)
Explain why calcium nitrate is less thermally stable than barium nitrate.
(3)
A qualitative test for nitrate ions involves heating an alkaline solution of the suspected nitrate with aluminium.
Complete the ionic equation for this redox reaction, using oxidation numbers. State symbols are not required.
8Al +........ NO3– +........ OH– +........ H2O 
........ Al(OH)4– +........ NH3
(1)
Describe a test to confirm that ammonia, NH3, has been produced.
(1)
Compare and contrast the reactions of bromine with benzene and of bromine with cyclohexene.
Consider the types of reaction that occur, the products that form, and any special conditions that may be required. Justify your answers.
Detailed mechanisms for the reactions are not required.
(6)
An ester Q has the molecular formula C8H16O2.
When hydrolysed, 2.07 g of Q formed a carboxylic acid with a 78 % yield. Once separated, the carboxylic acid was neutralised using excess sodium hydrogencarbonate solution.
NaHCO3 + RCOOH RCOO–Na+ + H2O + CO2
In this reaction, 269 cm3 of carbon dioxide gas was produced at room temperature and pressure.
Show that these data confirm that the relative molecular mass of Q is 144.
(3)
The high resolution proton NMR spectrum of ester Q was obtained. The structure of the ester Q is shown.
Explain the expected splitting pattern for the peak due to proton environment A circled in the structure.
(2)
Label the structure to indicate the remaining equivalent proton environments in ester Q.
(1)
Predict the chemical shifts, relative peak areas and splitting patterns in the high resolution proton NMR spectrum, due to the proton environments you have labelled. Do not consider proton environment A.
(3)
The alcohol 1-ethylcyclohexan-1-ol can be synthesised from cyclohexene using the reaction scheme shown.
Draw the mechanism for Step 1. Include curly arrows, and relevant lone pairs and dipoles.
(4)
Devise a reaction scheme for Step 2 and Step 3 of the synthesis. Include in your answer all reagents and conditions, the type of reaction in each step, and the structure of A.
(5)
Name the solvent used.
(1)
Explain why the anhydrous calcium chloride in Tube X is necessary.
(2)
Give a reason why it is best practice for the water in the condenser to flow in the direction shown in the diagram.
(1)
Carbonyl compounds such as cyclohexanone can be identified by the reaction with 2,4-dinitrophenylhydrazine.
Give the colour of the precipitate formed in this reaction.
(1)
Complete the simplified mechanism for the first two steps of this reaction by adding four curly arrows.
(4)
Describe how you would obtain pure dry crystals from the precipitate.
(4)
This question is about acids and bases.
Explain why this procedure would give invalid results.
(3)
State how Step 1 should be amended to give valid results.
(1)
(3)
Calculate the mass of sodium ethanoate needed to be dissolved in 250 cm3 of 0.520 mol dm–3 ethanoic acid to form a buffer solution with pH = 4.48
[Ka for ethanoic acid = 1.74×10–5mol dm–3]
(5)
A student mixes 50.0 cm3 of 0.900 mol dm–3 NaOH(aq) with 20.0 cm3 of 0.400 mol dm–3 H2SO4(aq).
Calculate the pH of the resultant solution.
[Ionic product of water, Kw = 1.00×10–14 mol2 dm–6]
(5)
Acidity in wine is mainly due to the dicarboxylic acid tartaric acid, C4H6O6.
Sulfur dioxide is added to wine as an antioxidant, to prevent the colour and flavour of the wine from deteriorating. It also inhibits the growth of bacteria.
The concentration of tartaric acid and the concentration of sulfur dioxide present in wine can both be determined by titrations.
State a precaution you would take in carrying out Step 3. Justify your answer.
(2)
Explain what effect the omission of Step 3 would have on the titre.
(2)
A mean titre of 20.60 cm3 was obtained.
Calculate the concentration, in g dm–3, of tartaric acid in the white wine.
(3)
A student carrying out the experiment forgot to remove an air bubble from the tip of the burette before carrying out a titration. During the titration, the air bubble escaped.
Explain the effect this mistake would have on the value of this titre.
(2)
A student carrying out the experiment obtained a titre of 11.80 cm3. The maximum permitted level of sulfur dioxide in white wine in the UK is 200 mg dm–3.
Show by calculation that the concentration of sulfur dioxide in the white wine is below the permitted maximum.
(4)
Explain how the addition of sodium hydrogencarbonate in Step 2 reduces the loss of sulfur dioxide from the flask.
(2)
Explain the purpose of the crushed ice in Step 3.
(2)
Explain why Step 6 is carried out before the final sample is removed and titrated in Step 7.
(2)
Some data from the experiment are shown. Vfinal is the titre volume from Step 7, Vt is the titre volume at time t.
| Time reaction sample is added to crushed ice / min | 0 | 10 | 20 | 30 | 40 | 50 | 60 |
| Vfinal – Vt of sodium hydroxide / cm3 | 11.60 | 6.50 | 3.80 | 1.80 | 0.90 | 0.80 | 0.80 |
Plot a graph of the Vfinal – Vt of sodium hydroxide against the time the reaction sample is added to the crushed ice.
(3)
Explain why Vfinal – Vt is plotted rather than the concentration of sodium hydroxide solution for each titre.
(2)
Determine two half-lives for the reaction, showing your working on the graph.
(2)
Deduce the order of the reaction, using your answer from (b)(iii) to justify your deduction.
(1)
Ethyl ethanoate can also be hydrolysed under alkaline conditions.
A student researching the mechanism for the reaction found this example.
Deduce a rate equation that is consistent with this reaction mechanism. Justify your answer.
(2)
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