Titrations, standard solutions and uncertainty (Core Practicals 3 and 4): Edexcel International A Level Chemistry questions

Edexcel International A Level Chemistry past-paper questions on 8.B.6 Titrations, standard solutions and uncertainty (Core Practicals 3 and 4), 2019–2025, with mark schemes and examiner’s reports where available.

All 118 questions on Titrations, standard solutions and uncertainty (Core Practicals 3 and 4), as a list

June 2025, AS Unit 2, Q17(a) (7 marks): The value of n in a sample of a hydrated magnesium carbonate, MgCO3∙nH2O , can be determined by the reaction with hydrochloric acid. The equation for the reacti
June 2025, Unit 6, Q2(b) (2 marks): Give the name of a suitable indicator to use in Step 4, including the expected colour change at the end-point. (2) Name of indicator Colour change from to
June 2025, Unit 6, Q2(c)(i) (2 marks): Complete the table and calculate the mean titre in cm3. (2)
June 2025, Unit 6, Q2(c)(ii) (4 marks): The equation for the titration is shown. Ca(OH)2(aq) + 2HCl(aq) → CaCl2(aq) + 2H2O(l) A data book value for the concentration of a saturated solution of calcium
January 2025, AS Unit 2, Q12(a) (1 mark): What is the concentration of the sodium hydroxide solution? (1) A 0.176 mol dm–3 B 0.239 mol dm–3 C 0.351 mol dm–3 D 0.702 mol dm–3
January 2025, AS Unit 2, Q12(b) (1 mark): What is the percentage error in the titre? [The burette is accurate to 0.05 cm3 per reading] (1) A 0.10% B 0.34% C 0.40% D 0.68%
January 2025, AS Unit 2, Q17(c) (2 marks): Another student suggested that the reaction between manganate(VII) and rhubarb juice could be used to find the concentration of ethanedioic acid in rhubarb juic
January 2025, AS Unit 3, Q3(a) (1 mark): State what is meant by the term standard solution. (1)
January 2025, AS Unit 3, Q3(b) (6 marks): Describe the preparation of 100.0 cm3 of a 0.0500 mol dm–3 standard solution of ethanedioic acid, starting with crystals of ethanedioic acid dihydrate, H2C2O4.2
January 2025, AS Unit 3, Q3(c)(i) (1 mark): Name the piece of apparatus that should be used to add the ethanedioic acid solution, H2C2O4(aq), to the conical flask. (1)
January 2025, AS Unit 3, Q3(c)(ii) (2 marks): The titration was carried out with a few drops of phenolphthalein indicator in the conical flask. State the colour change observed at the end‑point of the titra
January 2025, AS Unit 3, Q3(c)(iv) (3 marks): The titration was repeated, giving a mean titre of 31.55 cm3. Calculate the concentration of the barium hydroxide solution, Ba(OH)2(aq), in g dm–3. Ba(OH)2 and
October 2024, AS Unit 2, Q7 (1 mark): Sulfuric acid and sodium hydroxide react as shown. H2SO4(aq) + 2NaOH(aq) → Na2SO4(aq) + 2H2O(l) Which sample of sulfuric acid solution will be exactly neutralis
October 2024, AS Unit 3, Q2(a)(ii) (2 marks): Calculate the concentration of the sodium hydroxide solution, using an answer from (a)(i) and information from the procedure. (2)
October 2024, AS Unit 3, Q2(c)(i) (1 mark): Give an improvement to the experimental method that will increase the accuracy of the calculated titre value. (1)
October 2024, Unit 6, Q3(a)(i) (3 marks): Describe how to make 250.0 cm3 of a solution of ethanedioic acid in Step 1. (3)
June 2024, AS Unit 2, Q11(a) (1 mark): The titration is carried out using methyl orange as an indicator. What would be the colour change at the end‑point of the titration? (1) A orange to red B red t
June 2024, AS Unit 2, Q11(b) (1 mark): What is the concentration, in mol dm–3, of the potassium sulfate solution produced by this reaction at the end‑point, to 2 significant figures? (1) A 0.010 B 0.
June 2024, AS Unit 2, Q11(c) (1 mark): Information about the uncertainties in each reading used to measure the volumes of the solutions in this titration is shown. Uncertainty / cm3 Solution Equipmen
June 2024, AS Unit 2, Q17(b) (1 mark): Calculate the number of moles of ammonia added at the end‑point. (1)
June 2024, Unit 6, Q5(b)(i) (4 marks): Calculate the molar mass of NH4X. Use the data from Steps 1 and 2. (4)
June 2024, Unit 6, Q5(c) (4 marks): Another student carried out the experiment but did not titrate all the contents of the conical flask in Step 6. Instead they transferred the contents of the con
June 2024 (R), AS Unit 3, Q3(a) (2 marks): Phenolphthalein indicator was used in the experiment. State the colour change seen at the end-point. (2)
June 2024 (R), AS Unit 3, Q3(b) (1 mark): Calculate the mean titre of sodium hydroxide solution using the concordant results. (1)
June 2024 (R), AS Unit 3, Q3(c) (2 marks): Calculate the concentration of the maleic acid solution in mol dm–3. [Mr maleic acid = 116] (2)
June 2024 (R), AS Unit 3, Q3(d) (3 marks): Use your answers to (b) and (c) to calculate the concentration of the sodium hydroxide solution in mol dm–3. (3)
January 2024, AS Unit 3, Q2(a) (1 mark): Draw a circle around the concordant results in the table. (1)
January 2024, AS Unit 3, Q2(b) (1 mark): Calculate the mean titre, using your answer from (a). (1)
January 2024, AS Unit 3, Q2(c)(i) (1 mark): State the colour change that occurs at the end‑point of the titration. (1)
January 2024, AS Unit 3, Q2(c)(ii) (5 marks): Calculate the percentage by mass of citric acid in the lemon juice, using your mean titre from (b). Give your answer to two significant figures. [Concentration
January 2024, AS Unit 3, Q2(d) (1 mark): Suggest a possible reason why the value obtained in (c) is valid, even though lemon juice also contains some ascorbic acid and malic acid. (1)
January 2024, AS Unit 3, Q2(e)(i) (1 mark): Student B added too much deionised water in Step 2. State how Student B should correct this mistake. (1)
January 2024, AS Unit 3, Q2(e)(ii) (2 marks): Student C used sodium hydroxide solution labelled 0.103 mol dm–3 that had been made up several months ago and stored since then. Explain what effect this would
October 2023, AS Unit 2, Q20(b)(i) (4 marks): Calculate the concentration of the saturated solution, in g dm–3. (4)
October 2023, AS Unit 3, Q4(a) (2 marks): State the colour change of the indicator at the end-point of the titration. (2) From to
October 2023, AS Unit 3, Q4(b) (1 mark): The diagram shows the burette at the end-point of the rough titration. 23 24 25 Give the burette reading for this rough titration. (1)
October 2023, AS Unit 3, Q4(c) (3 marks): The student refilled the burette and prepared a second conical flask by adding sodium carbonate solution and methyl orange indicator. Describe how an accurate t
October 2023, AS Unit 3, Q4(d) (3 marks): The mean titre from two accurate titrations was 22.65 cm3 . Calculate the concentration of the hydrochloric acid, in mol dm−3 . The equation for the reaction is
October 2023, Unit 5, Q21(f) (6 marks): Acetylsalicylic acid in aspirin tablets is hydrolysed by excess sodium hydroxide. CH3COOC6H4COOH + 2NaOH → CH3COONa + HOC6H4COONa + H2O The unreacted sodium hyd
June 2023, AS Unit 3, Q4(c)(i) (2 marks): State the colour change observed in the conical flask at
June 2023, AS Unit 3, Q4(c)(ii) (2 marks): Complete the table and use the concordant results to calculate the mean titre. (2)
June 2023, AS Unit 3, Q4(c)(iii) (4 marks): The reaction taking place in this titration is Ca(OH)2(aq) + 2HCl(aq) → CaCl2(aq) + 2H2O(l) Calculate the concentration of the calcium hydroxide solution in g d
January 2023, AS Unit 3, Q3(a)(i) (2 marks): In Step 1, the student rinsed both the pipette and the volumetric flask with deionised water before transferring 25.0 cm3 of solution A. State the effect, if an
January 2023, AS Unit 3, Q3(a)(ii) (1 mark): Give a reason why the student inverted the volumetric flask several times in Step 1. (1)
January 2023, AS Unit 3, Q3(a)(iv) (2 marks): State the colour change of the phenolphthalein indicator at the end‑point of the titration in Step 3. (2) From to
January 2023, AS Unit 3, Q3(a)(v) (1 mark): The results of the student’s experiment are shown. Titration Trial 1 2 3 4 Final volume / cm3 29.25 33.25 32.00 29.50 28.90 Initial volume / cm3 0.00 4.50 3.15
January 2023, AS Unit 3, Q3(a)(vi) (1 mark): Give a reason why the student did not need to carry out titrations 3 and 4. (1)
January 2023, AS Unit 3, Q3(a)(vii) (1 mark): Give a reason why solution A was diluted before titrating it with this sodium hydroxide solution. (1)
January 2023, AS Unit 3, Q3(b)(ii) (5 marks): Calculate the concentration of citric acid in solution A in g dm–3, using the equation from (b)(i) and the results from (a)(v). Give your answer to three signif
January 2023, AS Unit 3, Q3(b)(iii) (2 marks): Using the result of the experiment, the student concluded that the stated concentration of the descaler (200 g dm–3) was incorrect. State whether or not this di
October 2022, AS Unit 2, Q19 (1 mark): A student carries out two sets of titrations, one using methyl orange and the other using phenolphthalein as indicators. The conical flask contains sodium hydro
October 2022, AS Unit 3, Q2(a)(i) (1 mark): Complete the table. (1)
October 2022, AS Unit 3, Q2(a)(ii) (1 mark): Calculate the mean titre for the titration. (1)
October 2022, AS Unit 3, Q2(b)(i) (2 marks): Calculate the number of moles of sulfuric acid that reacted with the sodium hydroxide in the mean titre, using your answer from (a)(ii). (2)
October 2022, AS Unit 3, Q2(b)(ii) (1 mark): Calculate the total number of moles of sulfuric acid used at the start of the experiment. (1)
October 2022, AS Unit 3, Q2(b)(iii) (4 marks): Calculate the percentage of magnesium carbonate in the antacid tablet, using your answers to (b)(i) and (b)(ii). You must show all your working. (4) MgCO3 + H2S
October 2022, AS Unit 3, Q2(c)(i) (1 mark): Give one possible reason for carrying out a rough titration. (1)
October 2022, AS Unit 3, Q2(c)(ii) (2 marks): Phenolphthalein indicator was used in the titration. State the colour change seen at the end‑point. (2) From to
October 2022, Unit 6, Q2(b) (2 marks): Describe how to make the 250.0 cm3 of sodium hydroxide solution in Step 4. (2)
October 2022, Unit 6, Q2(c) (5 marks): The mean titre was 12.75 cm3. Calculate the percentage by mass of ammonium sulfate, (NH4)2SO4 , in the sample of plant fertiliser. [Relative formula mass of (NH
October 2022, Unit 6, Q2(d)(i) (3 marks): Explain the effect, if any, on the titre value and hence on the calculated percentage of ammonium sulfate in the fertiliser. (3)
June 2022, AS Unit 2, Q9(a) (1 mark): What is the colour change of the indicator at the end-point of this titration? (1) A red to orange B red to yellow C yellow to orange D yellow to red
June 2022, AS Unit 2, Q9(b) (1 mark): A student carried out the first titration and did not notice that there was an air bubble between the tap and the tip of the burette. During the titration, the
June 2022, AS Unit 2, Q9(c) (1 mark): 25.0 cm3 of 0.100 mol dm−3 aqueous sodium hydroxide required a mean titre of 18.70 cm3 of sulfuric acid. 2NaOH(aq) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l) What is th
June 2022, AS Unit 3, Q2(a) (4 marks): Calculate the value for the Ar of the metal M from the data of the first student. MHCO3 and HCl react in a 1 : 1 ratio. You must show your working. Give your an
June 2022, AS Unit 3, Q2(b)(i) (1 mark): Calculate the experimental error for the second student. [Ar of potassium = 39.1] (1)
June 2022, AS Unit 3, Q2(b)(ii) (3 marks): The second student calculated the Ar value of M to be 37.52 with a total percentage uncertainty of 4.5 %. Comment on the value of 37.52 obtained by this student
June 2022, AS Unit 3, Q2(b)(iii) (2 marks): The first student suggested that the burette was the biggest source of experimental uncertainty. Explain how the percentage uncertainty of the burette reading c
June 2022, AS Unit 3, Q2(b)(iv) (4 marks): The second student was told that using a beaker to prepare their standard solution was incorrect. Describe the steps the student should take to make a standard
January 2022, AS Unit 2, Q15 (1 mark): A titre of 13.25 cm3 was obtained using a 50 cm3 burette. What is the percentage uncertainty in the titre? [Each reading of the burette has an uncertainty of ±
October 2021, AS Unit 2, Q21(b)(i) (2 marks): The indicator used was phenolphthalein. State the colour change at the end-point. (2) from to
October 2021, AS Unit 2, Q21(b)(ii) (4 marks): Calculate the relative atomic mass of M and use it to identify the Group 1 metal, M. (4)
October 2021, AS Unit 2, Q21(c) (2 marks): Another student repeated the experiment, using a different sample of metal M, but did not wipe off the oil before weighing it. State how this would change the c
October 2021, AS Unit 3, Q5(a) (1 mark): Complete the titre values. (1) Titration number Rough 1 2 3 4 Final reading 24.90 21.25 42.85 21.80 43.15 / cm3 Initial reading 2.30 0.00 21.25 0.50 21.80 / cm3
October 2021, AS Unit 3, Q5(b)(i) (1 mark): State why the value from Titration 2 was not used to calculate the mean. (1)
October 2021, AS Unit 3, Q5(b)(ii) (4 marks): Calculate the concentration of the sodium hydroxide solution in mol dm−3. (4)
October 2021, AS Unit 3, Q5(c) (1 mark): Each reading of the burette has an uncertainty of ±0.05 cm3. Calculate the percentage uncertainty in Titration 4. (1)
October 2021, AS Unit 3, Q5(d) (2 marks): State the colour change that would be seen at the end-point in this titration using phenolphthalein as the indicator. (2) From to
June 2021, AS Unit 2, Q15(b) (1 mark): 25.0 cm3 of the sodium hydroxide solution prepared in (a) was placed in a conical flask and titrated with sulfuric acid. 2NaOH + H2SO4 → Na2SO4 + 2H2O Calculate
June 2021, AS Unit 2, Q15(c) (1 mark): Phenolphthalein indicator was used for the titration in (b). What was the colour change at the endpoint? (1) A colourless → pink B pink → colourless C orange →
June 2021, AS Unit 3, Q3(a) (2 marks): State the colour change observed at the end-point of the titration. (2) From to
June 2021, AS Unit 3, Q3(b)(i) (1 mark): Complete the table. (1)
June 2021, AS Unit 3, Q3(b)(ii) (1 mark): Give a reason why the first titre should not be used to calculate the mean titre. (1)
June 2021, AS Unit 3, Q3(b)(iii) (2 marks): Calculate the number of moles of hydrochloric acid in the mean titre. (2)
June 2021, AS Unit 3, Q3(b)(iv) (3 marks): The equation for the reaction in the titration is Ba(OH)2(aq) + 2HCl(aq) → BaCl2(aq) + 2H2O(l) Calculate the concentration of barium hydroxide, in g dm−3, givin
January 2021, AS Unit 2, Q18 (1 mark): Barium chloride solution, BaCl2(aq), reacts with gallium sulfate solution, Ga2(SO4)3(aq) to form a precipitate of barium sulfate, BaSO4(s). What is the minimum
January 2021, AS Unit 3, Q2(a)(i) (1 mark): Give a possible reason why any solution remaining in the beaker is washed into the volumetric flask before making up to the mark. (1)
January 2021, AS Unit 3, Q2(a)(ii) (2 marks): Calculate the concentration of this standard solution of ethanedioic acid in mol dm–3. Give your answer to an appropriate number of significant figures. [Molar
January 2021, AS Unit 3, Q2(b)(i) (1 mark): Explain why the burette is rinsed with ethanedioic acid solution in Step 2. (1)
January 2021, AS Unit 3, Q2(b)(ii) (2 marks): The diagram shows how the student read the filled pipette in Step 3. Identify the two mistakes the student made. (2) 25 cm3 ± 0.06 pipette B20 °C mark
January 2021, AS Unit 3, Q2(b)(iii) (2 marks): The student completely emptied the pipette for each transfer in Step 3. Explain the effect on the titre of completely emptying the pipette rather than leaving a
January 2021, AS Unit 3, Q2(b)(iv) (2 marks): State the colour change in the conical flask at the end-point. (2) From to
January 2021, AS Unit 3, Q2(c)(i) (2 marks): Complete the table and calculate the mean titre. (2)
January 2021, AS Unit 3, Q2(c)(ii) (3 marks): Calculate the concentration of the sodium hydroxide solution in mol dm–3. The equation for the titration is (COOH)2 + 2NaOH → (COONa)2 + 2H2O (3)
January 2021, Unit 4, Q11 (1 mark): A diprotic acid, H2A, was titrated with sodium hydroxide solution. H2A(aq) + 2NaOH(aq) o Na2A(aq) + 2H2O(l) A 25.0 cm3 portion of 0.100 mol dm−3 sodium hydroxid
October 2020, AS Unit 2, Q14(b) (4 marks): The concentration of a saturated solution of calcium hydroxide can be determined by titration. 25.0 cm3 portions of a saturated solution of calcium hydroxide we
October 2020, AS Unit 3, Q5(a) (1 mark): Name a suitable piece of apparatus to measure the 25.0 cm3 of solution. (1)
October 2020, AS Unit 3, Q5(b) (2 marks): Methyl orange indicator was used in this titration. Give the colour change in the conical flask at the end-point. (2) Colour change from to
October 2020, AS Unit 3, Q5(c)(i) (1 mark): Complete the table. (1)
October 2020, AS Unit 3, Q5(c)(ii) (1 mark): Using appropriate titrations, calculate the mean titre. (1)
October 2020, AS Unit 3, Q5(c)(iii) (1 mark): Using your answer to (c)(ii), calculate the number of moles of HCl in the mean titre. (1)
October 2020, AS Unit 3, Q5(c)(iv) (2 marks): Calculate the number of moles of M2CO3 in 25.0 cm3 of the solution. Hence calculate the number of moles of M2CO3 in the 250.0 cm3 volumetric flask. (2)
October 2020, AS Unit 3, Q5(c)(v) (1 mark): Using your answer in (c)(iv) and the mass of M2CO3.10H2O in the 250 cm3 of solution, calculate the molar mass of M2CO3.10H2O. (1)
October 2020, AS Unit 3, Q5(c)(vi) (2 marks): Use your answer to (c)(v) to identify metal M. (2)
January 2020, AS Unit 2, Q15(d)(i) (2 marks): Calculate the amount, in moles, of sodium carbonate in the 250.0 cm3 of solution. (2)
January 2020, AS Unit 2, Q15(d)(ii) (4 marks): The 250.0 cm3 of solution was prepared by dissolving 3.29 g of Na2CO3.xH2O. Use this mass and your answer to (d)(i) to determine the value of x. Give your answe
January 2020, AS Unit 3, Q3(a) (2 marks): The indicator used was methyl orange. State the colour change at the end-point. (2) From to
January 2020, AS Unit 3, Q3(b)(i) (2 marks): Complete the table and, using appropriate titrations, calculate the mean titre. (2)
January 2020, AS Unit 3, Q3(b)(ii) (5 marks): Calculate the percentage purity, by mass, of the sodium carbonate. (5)
June 2019, AS Unit 2, Q23(d)(i) (2 marks): Phenolphthalein is a suitable indicator for this titration. State the colour change at the end-point. (2)
June 2019, AS Unit 2, Q23(d)(ii) (2 marks): Suggest two possible reasons why the titre for Run 1 is greater than the other two titres. (2)
June 2019, AS Unit 2, Q23(d)(iii) (5 marks): The equation for the reaction of propanoic acid with sodium hydroxide is CH3CH2COOH + NaOH → CH3CH2COONa + H2O Calculate the mass in grams of propanoic acid ext
June 2019, AS Unit 2, Q23(d)(iv) (2 marks): Use your answer to (d)(iii) to determine whether the acid in this sample lies within the permitted range for use in animal feed. (2)
June 2019, AS Unit 2, Q23(d)(v) (1 mark): Suggest how the animal feed would be affected if the amount of propanoic acid was outside the permitted range. (1)
June 2019, AS Unit 3, Q4(a) (1 mark): State what is meant by the term ‘concordant results’. (1)
June 2019, AS Unit 3, Q4(b) (1 mark): Using appropriate titres, calculate the mean titre. (1)
June 2019, AS Unit 3, Q4(c) (2 marks): State the colour change at the endpoint of the titration. (2) From to
June 2019, AS Unit 3, Q4(d) (4 marks): The equation for the reaction is NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l) Calculate the purity of the sodium hydroxide, NaOH, as a percentage by mass. (4)

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