Edexcel A Level Chemistry Paper 3: General and Practical Principles in Chemistry November 2021 question paper 9CH0/03

This question is about chlorine.

Chlorine has two isotopes with mass numbers 35 and 37.

Complete the table to show the numbers of subatomic particles in a³⁵Cl atom

A sample of chlorine contained 75% of³⁵Cl and 25% of³⁷Cl.

Complete the mass spectrum to show the peaks you would expect for the molecular ion Cl⁺₂ from this sample of chlorine gas.

Write the formula of potassium chlorate(V).

Write the equation for the first electron affinity of chlorine. Include state symbols.

The standard electrode potential for the chlorine/chloride ion half-cell is

Identify an oxidising agent from the Data Booklet that will convert chloride ions into chlorine under standard conditions.

Calculate the value of for the reaction in (d)(i).

Analysis shows that a compound has the molecular formula C₄H₈O₂.

A student suggests that the compound could be either A or B.

CH₃CH₂CH₂COOH or HOCH₂CHCHCH₂OH A B

Deduce a chemical test which would give a positive result for A but not for B. Include the reagent and observation.

Deduce a chemical test which would give a positive result for B but not for A. Include the reagent and observation.

This question is about aluminium chloride.

Complete the electronic configuration of an aluminium atom.

At high temperatures, aluminium chloride exists as AlCl₃ molecules.

Draw a dot-and-cross diagram of an aluminium chloride molecule, AlCl₃. Show the outer shell electrons only.

Aluminium chloride is used as a catalyst in the alkylation of benzene.

Draw the mechanism for the reaction between benzene and chloromethane using aluminium chloride as the catalyst. Include an equation for the formation of the electrophile, and any relevant curly arrows.

Aluminium chloride exists as a dimer, Al₂Cl₆, just above its boiling temperature.

Draw a diagram to show how two AlCl₃ molecules are joined together in the dimer.

State the type of bond that joins the two AlCl₃ molecules together.

A series of experiments was carried out to investigate the factors which affect the rate of reaction between calcium carbonate and dilute hydrochloric acid.

• 50.0 cm³ of hydrochloric acid was added to 10 g of calcium carbonate (an excess) in a conical flask placed on an electronic balance.

• The loss in mass of the flask and its contents was recorded every 30 seconds for 10 minutes.

• The experiment was repeated using different sized pieces of calcium carbonate, a different concentration of hydrochloric acid or a different temperature.

The results of Experiment 1 are shown on the graph.

Draw curves on the graph to show the results you would expect for Experiments 2, 3 and 4. Label the curves 2, 3 and 4.

A student was required to devise an alternative method of carrying out this experiment that involved collecting the gas produced.

Outline the procedure that the student could use, including a diagram and the measurements needed.

Tests are carried out on aqueous solutions of two salts, X and Y.

X contains one cation and one anion.

The observations for each test are recorded in the table.

Complete the table by writing the names or formulae of the species.

Write the ionic equation for the reaction between the cation in X and aqueous sodium hydroxide in Test 1. Include state symbols.

Give a reason why the green precipitate turns brown on the top after a few minutes.

Give a reason why dilute hydrochloric acid is needed in Test 2.

Y contains one cation and one anion.

The observations for each test are recorded in the table.

Complete the table by writing the names or formulae of the species.

Give the formula of the complex ion present in the deep blue solution at the end of Test 3.

Give a reagent that could be added to the mixture at the end of Test 4 to confirm the identity of the anion in Y. Include the observation when this reagent is added.

This question is about the preparation and analysis of paracetamol.

Paracetamol may be prepared from phenol in three stages.

In Stage 1, phenol is nitrated using dilute nitric acid.

The nitration of benzene requires concentrated nitric acid at 55C with a catalyst of concentrated sulfuric acid. Both these reactions are electrophilic substitution.

Explain why phenol can be nitrated using milder conditions than benzene.

A mixture of 2-nitrophenol and 4-nitrophenol is produced in Stage 1. They are separated by steam distillation.

The boiling temperature of 2-nitrophenol is 215C and that of 4-nitrophenol is 279C.

Explain, in terms of intermolecular forces, why 4-nitrophenol has a higher boiling temperature than 2-nitrophenol. You may include a diagram in your answer.

State the type of reagent needed to convert 4-nitrophenol into 4-aminophenol in Stage 2.

The outline procedure for Stage 3 is:

• place 1.0 g of 4-aminophenol in a conical flask. Add 9 cm³ of distilled water and stir the mixture

• add 1 cm³ of ethanoic anhydride to the flask and shake the mixture until a precipitate of impure paracetamol forms

• remove the paracetamol by filtration under reduced pressure

• recrystallise the paracetamol using water as the solvent

• determine the melting temperature of the pure, dry paracetamol.

Draw a labelled diagram of the apparatus used for filtration under reduced pressure.

Describe the recrystallisation process to obtain a pure, dry sample of paracetamol.

The melting temperature of pure paracetamol is 170C.

Describe what happens to the melting temperature if the paracetamol is not pure.

The percentage by mass of paracetamol in three brands of paracetamol tablets are shown in the table.

The amount of paracetamol in a tablet can be determined using a titration with cerium(IV) ions.

The tablets are crushed and then hydrolysed in acid to form 4-aminophenol.

4-aminophenol is oxidised by cerium(IV) ions.

A tablet from one of the three brands of paracetamol was analysed following the outline procedure.

• one of the tablets was crushed and 0.500 g of the powder was added to dilute sulfuric acid

• the mixture was heated under reflux until the hydrolysis was complete

• the solution was made up to 100.0 cm³ in a volumetric flask

• 25.0cm³ portions of the solution were titrated against 0.100 mol dm⁻³ Ce⁴ using ferroin as indicator

Result

The mean titre was 16.50 cm³.

Give the molecular formula of paracetamol.

Determine, by calculation, which brand of tablet was analysed.

The enthalpy change for the decomposition of sodium hydrogencarbonate can be determined indirectly using Hess’s Law.

A student carried out two experiments.

Experiment 1 involved the reaction between sodium hydrogencarbonate and hydrochloric acid.

The student used the following procedure:

• use a measuring cylinder to measure 50 cm³ of 2.00 mol dm⁻³ hydrochloric acid and pour it into a polystyrene cup

• measure the initial temperature of the acid

• weigh the test tube containing sodium hydrogencarbonate

• tip the sodium hydrogencarbonate into the hydrochloric acid in the polystyrene cup, stir the mixture and record the lowest temperature reached

• weigh the empty test tube.

Complete the table.

Show, by calculation, that the hydrochloric acid is in excess. You must show your working.

Calculate the enthalpy change for the reaction between sodium hydrogencarbonate and hydrochloric acid, using the results of the experiment. Include a sign and units in your answer.

Assume: mass of reaction mixture 50.0 g f₋₁₋₁ p specific heat capacity of the reaction mixture 4.18 J g C

Experiment 2 involved the reaction between sodium carbonate and hydrochloric acid.

The student repeated the procedure for Experiment 1 but used sodium carbonate instead of sodium hydrogencarbonate and measured the maximum temperature rise.

The student calculated the enthalpy change for this reaction as −29.4 kJ mol⁻¹.

Complete the Hess cycle with appropriate formulae and labelled arrows.

Calculate the enthalpy change for the decomposition of sodium hydrogencarbonate. Include a sign and units in your answer.

Another student carried out the same two experiments and obtained a value for the enthalpy change of decomposition of sodium hydrogencarbonate of 74 kJ mol⁻¹.

The data book value for this enthalpy change is 90 kJ mol⁻¹.

Calculate the percentage error in this student’s value.

Calculate the percentage uncertainties in measuring 50 cm³ of hydrochloric acid using a burette and using a measuring cylinder.

Give a reason why using a burette rather than a measuring cylinder will not improve the accuracy of the experiment.

Describe changes to the method and how the data is used that would improve the accuracy of the determination of the temperature change in Experiment 2. Your description should involve the use of a clock and plotting a graph.

This question is about some carbonyl compounds with the molecular formula C₅H₁₀O.

Describe a chemical test, and its result, to distinguish between pentan-2-one, CH₃CH₂CH₂COCH₃, and pentan-3-one, CH₃CH₂COCH₂CH₃.

Pentan-2-one reacts with hydrogen cyanide in the presence of cyanide ions to form 2-hydroxy-2-methylpentanenitrile.

Draw the mechanism for the reaction between pentan-2-one and hydrogen cyanide in the presence of cyanide ions.

Include curly arrows and any relevant lone pairs.

The product of this reaction, 2-hydroxy-2-methylpentanenitrile, has a chiral centre. Explain why a racemic mixture of 2-hydroxy-2-methylpentanenitrile is formed in this reaction.

An aldehyde with molecular formula C₅H₁₀O has a¹³C NMR spectrum with three peaks.

The high resolution¹H NMR spectrum of this aldehyde has two peaks and neither of them is split.

Deduce the displayed formula of this aldehyde. Justify your answer by referring to both NMR spectra.

*(d) Describe the oxidation and reduction reactions of pentanal and pentan-3-one.

Include the reagents and the structures of the organic products formed in any reactions that take place.

Ammonia is manufactured by the Haber Process.

The pressure used in the Haber Process is 200 atm.

Explain the effect, if any, of increasing the pressure on the equilibrium yield of ammonia.

The equilibrium constants for K_p and K_c are related by the equation

where ∆n is the number of moles of reactants minus the number of moles of products.

Calculate the value of K_c at 500 K when the value of K_p 3.55 × 10⁻² atm⁻². Include the units for K_c.

[Use the value of R 0.0821 dm³ atm K⁻¹ mol⁻¹]

A mixture of 1.0 mol of nitrogen and 3.0 mol of hydrogen is left to reach equilibrium at 700 K.

Calculate the total pressure, in atmospheres, needed to produce a yield of 0.30 mol of ammonia at 700 K. Give your answer to an appropriate number of significant figures.

You must show your working.

[K_p 7.76 × 10⁻⁵ atm⁻² at 700 K]

The value of the equilibrium constant, K_p, varies with temperature. The equation relating the values of the equilibrium constant at two temperatures is

The equilibrium constant, K₁, for the formation of ammonia is 6.76 10⁵ atm⁻² when the temperature T₁ 298 K. The enthalpy change ∆H −92400 J mol⁻¹.

Calculate the value of the equilibrium constant for this reaction at 310 K.

[Use the value of R 8.31 J mol⁻¹ K⁻¹]