Acid–base titrations

The concentration of aqueous sodium carbonate can be determined by allowing it to react with hydrochloric acid of known concentration, using methyl orange as the indicator. Which pieces of apparatus are required?

May/June 2015

Ammonium sulfate is a nitrogenous fertiliser. The nitrogen it contains helps plants to grow.

May/June 2015

‘Lawn sand’ consists of sand combined with iron(II) sulfate and ammonium sulfate, and it is used to encourage grass growth.

May/June 2015

A student is given a sample of an organic acid, V, and is told to work out its relative molecular mass and propose its molecular formula.

May/June 2016

A student receives a sample of an organic acid and must work out its relative molecular mass and infer its molecular formula.

May/June 2016

The diagram shows four pieces of apparatus used to measure the volume of a gas or a liquid. Which piece of apparatus must always be filled to the same level?

May/June 2017

A learner is asked to work out the percentage purity of an impure magnesium carbonate sample.

May/June 2017

A student is making sodium sulfate crystals by titration. First, the student places $25.0\,\text{cm}^3$ of $1.00\,\text{mol dm}^{-3}$ sodium hydroxide into a conical flask, then adds dilute sulfuric acid from a burette. Following each addition of sulfuric acid, the student measures and notes the pH of the mixture with a pH meter.

May/June 2017

A student carries out a set of titrations to work out the percentage of ethanoic acid in a vinegar sample. Diagrams of some of the apparatus used by the student are shown.

May/June 2018

A chemist intends to run an experiment to determine the acid concentration in lemon juice. The preparation of the solution and the titration method are outlined.

May/June 2018

During a volumetric titration, $25.0\,\text{cm}^3$ of $0.100\,\text{mol dm}^{-3}$ sodium hydroxide neutralises exactly $20.0\,\text{cm}^3$ of sulfuric acid. $2\text{NaOH} + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + 2\text{H}_2\text{O}$ Determine the concentration of the sulfuric acid?

May/June 2019

A liquid hydrocarbon is ignited in the apparatus shown.

May/June 2019

Milk of Magnesia is a liquid medicine that is used to relieve indigestion. Milk of Magnesia contains magnesium hydroxide, $\text{Mg(OH)}_2$. A student carries out a sequence of titrations to find the percentage by mass of magnesium hydroxide in Milk of Magnesia. Diagrams of some of the apparatus used by the student are shown.

May/June 2019

A student finds the concentration of dilute sulfuric acid, $\text{H}_2\text{SO}_4\text{(aq)}$, by carrying out a titration with aqueous sodium hydroxide, $\text{NaOH(aq)}$.

May/June 2021

A titration technique can be used to prepare soluble salts. A student carries out an experiment to obtain a pure sample of sodium chloride. Part of the procedure is shown in the diagram.

May/June 2021

The diagram illustrates a titration experiment. Which row correctly describes the reaction taking place in the conical flask?

May/June 2022

The stages for preparing a pure sample of sodium nitrate are given below. 1. Titrate until the end-point is reached using dilute nitric acid. 2. Heat to evaporate water and make the solution more concentrated. 3. Wash out the conical flask. 4. Put in indicator. 5. Use a pipette to transfer a measured volume of aqueous sodium hydroxide into a conical flask. 6. Allow to cool, then filter off the crystals. 7. Carry out the procedure again with the same volumes of aqueous sodium hydroxide and dilute nitric acid, but without indicator. Which sequence of steps is correct?

May/June 2022

A student finds the concentration of aqueous sodium hydroxide, $\text{NaOH(aq)}$, by titrating it with aqueous citric acid, $\text{C}_6\text{H}_8\text{O}_7\text{(aq)}$.

May/June 2022

A student works out the concentration of aqueous potassium manganate(VII), $\text{KMnO}_4$, by carrying out a titration with ethanedioic acid solution, $\text{H}_2\text{C}_2\text{O}_4$. The reaction may be represented by the equation shown below. $2\text{KMnO}_4 + 5\text{H}_2\text{C}_2\text{O}_4 + 6\text{H}^+ \rightarrow 2\text{Mn}^{2+} + 10\text{CO}_2 + 8\text{H}_2\text{O} + 2\text{K}^+$

May/June 2022

A sample of $25.0\,\text{cm}^3$ of $1.0\,\text{mol dm}^{-3}$ sodium hydroxide is titrated using dilute sulfuric acid and a suitable indicator. Reaching the end-point needs $25.0\,\text{cm}^3$ of the acid. What is the concentration of the sulfuric acid and which indicator is used?

May/June 2023

White vinegar is a colourless solution of ethanoic acid. A student carries out titrations of $0.400\,\text{mol dm}^{-3}$ aqueous sodium hydroxide with two vinegar samples, A and B. Four titrations are done in total, two with A and two with B. The student: Step 1 uses a volumetric pipette to place $25.0\,\text{cm}^3$ of $0.400\,\text{mol dm}^{-3}$ sodium hydroxide into a conical flask. Step 2 adds five drops of an indicator to the conical flask. Step 3 runs A from a burette into the flask while swirling the contents, then adds it drop by drop close to the end-point until the solution just changes colour. Step 4 empties the conical flask and rinses it with distilled water. Step 5 repeats steps 1 to 4. Step 6 repeats steps 1 to 5 using B instead of A.

May/June 2023

Two titrations involving dilute hydrochloric acid and aqueous sodium hydroxide are carried out with two different indicators, methyl orange and thymolphthalein. The reaction equation is given below. $\text{HCl(aq)} + \text{NaOH(aq)} \rightarrow \text{NaCl(aq)} + \text{H}_2\text{O(l)}$ A volumetric pipette is used to transfer $25.0\,\text{cm}^3$ of dilute hydrochloric acid into a conical flask containing a few drops of indicator. Aqueous sodium hydroxide is then delivered from a burette into the dilute hydrochloric acid until the end-point is reached. For each indicator, the end-point occurs when $23.6\,\text{cm}^3$ of aqueous sodium hydroxide has been added. Which of the following statements about this experiment are correct?

May/June 2024

In a titration, $25.0\,\text{cm}^3$ of $0.100\,\text{mol dm}^{-3}$ sodium hydroxide is exactly neutralised by $20.0\,\text{cm}^3$ of dilute sulfuric acid. $\text{2NaOH} + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + 2\text{H}_2\text{O}$ Calculate the concentration of the dilute sulfuric acid.

May/June 2024

A student determines the concentration of a dilute acid, HA(aq), by titration. The student: • places $25.0\,\text{cm}^3$ of aqueous sodium hydroxide into a conical flask • adds a few drops of methyl orange indicator to the aqueous sodium hydroxide • adds HA(aq) slowly to the aqueous sodium hydroxide until the methyl orange changes colour • notes the volume of HA(aq) added.

May/June 2024

A titration is carried out. $25.0\,\text{cm}^3$ of aqueous sodium hydroxide is placed into a conical flask. Several drops of methyl orange indicator are then added. Dilute hydrochloric acid is added drop by drop to the mixture until the colour changes. Which row is correct?

May/June 2025

The diagram illustrates how pH changes as a strong alkali is added to a weak acid. $40\,\text{cm}^3$ of a strong alkali is introduced into a weak acid, and a sample of the resulting solution is then tested separately using methyl orange and thymolphthalein. Which row is correct?

May/June 2025

Sample A is an impure form of calcium carbonate. A student works out the amount in moles of calcium carbonate present in a sample of A.

May/June 2025

Solid W is an impure organic acid, $\text{H}_3\text{A}$. To find the mass of $\text{H}_3\text{A}$ present in a sample of W, a student carries out a titration using $0.100\ \text{mol dm}^{-3}$ sodium hydroxide, NaOH. The student: step 1 puts the sample of W into a beaker step 2 adds 100 cm$^3$ of distilled water to the beaker with a measuring cylinder step 3 mixes until all of the solid has dissolved completely step 4 gives this mixture the label X step 5 uses a pipette to transfer 25.0 cm$^3$ of NaOH into a conical flask and adds five drops of phenolphthalein indicator step 6 pours X into the burette step 7 runs X into the conical flask until the solution just alters colour step 8 carries out the titration two further times.

May/June 2025

In a titration involving an acid in the burette and an alkali, the same titration flask may need to be used again. What is the most suitable way to rinse the flask?

Oct/Nov 2015

During a titration with an acid in the burette and an alkali, the same titration flask may have to be used again. Which rinsing procedure is the most suitable for the flask?

Oct/Nov 2015

A student uses titration to determine the percentage by mass of water in oxalic acid crystals.

Oct/Nov 2015

A student carries out an experiment to study the reaction of dilute sulfuric acid with aqueous sodium hydroxide.

Oct/Nov 2015

A student is working out the percentage by mass composition of a mixture made from two solids, sodium chloride, $\text{NaCl}$, and sodium carbonate, $\text{Na}_2\text{CO}_3$. This mixture is M.

Oct/Nov 2015

Limestone is calcium carbonate that is not pure. A student carries out an experiment to determine the percentage by mass of calcium carbonate in a limestone sample. The limestone is put into a container that has already been weighed, and the container is weighed again. mass of container + limestone = $10.22\text{ g}$ mass of empty container = $5.72\text{ g}$

Oct/Nov 2016

Vinegar is a dilute solution of ethanoic acid. Different brands of vinegar have different ethanoic acid concentrations. Two separate brands of colourless vinegar are supplied.

Oct/Nov 2016

A learner receives a contaminated sample of magnesium carbonate, $\text{MgCO}_3$. The learner works out what percentage of the sample’s mass is magnesium carbonate.

Oct/Nov 2017

A student receives an impure sample of calcium hydroxide, $\text{Ca(OH)}_2$. The student wants to find the percentage by mass of calcium hydroxide in the sample.

Oct/Nov 2017

A student carries out a titration by delivering aqueous sodium hydroxide from a burette into dilute hydrochloric acid in a conical flask. When the titration ends, the conical flask is emptied. What should be done before beginning the next titration?

Oct/Nov 2018

Ethanedioic acid crystals are represented by the formula $H_2C_2O_4\cdot xH_2O$. A student uses titration to find the value of $x$.

Oct/Nov 2018

A student uses a titration method to find the percentage of iron in a powdered sample of impure iron.

Oct/Nov 2018

The concentration of aqueous sodium carbonate can be determined by its reaction with hydrochloric acid of known concentration. The indicator methyl orange is used. Which items of apparatus are needed?

Oct/Nov 2019

The concentration of aqueous sodium carbonate can be determined by reacting it with hydrochloric acid of known concentration. Methyl orange is the indicator used. Which items of equipment are required?

Oct/Nov 2019

This question concerns chlorine-containing compounds.

Oct/Nov 2019

J is bleach. The student carries out an experiment to find the concentration of sodium chlorate(I), NaClO, in J.

Oct/Nov 2019

A student carries out an experiment to work out the percentage by mass of potassium iodate(V), $\text{KIO}_3$, in a specimen of impure potassium iodate(V). The impure potassium iodate(V) sample is put into a container that has already been weighed, and the container is weighed again. mass of container + impure potassium iodate(V) = $8.20\,\text{g}$ mass of empty container = $5.28\,\text{g}$

Oct/Nov 2019

In a titration experiment, an acid is put into a burette. The diagrams show part of the burette at the beginning of the titration and at the end-point. What volume of acid is used in the titration?

Oct/Nov 2020

When dilute nitric acid reacts with aqueous barium hydroxide: $2\text{HNO}_3(aq) + \text{Ba(OH)}_2(aq) \rightarrow \text{Ba(NO}_3)_2(aq) + 2\text{H}_2\text{O}(l)$

Oct/Nov 2020

A student receives dilute sulfuric acid labelled L. The concentration of L is found by titration. To measure and move $25.0\,\text{cm}^3$ of L into apparatus B, the student uses apparatus A. The diagrams display apparatus A and B. The student dilutes the $25.0\,\text{cm}^3$ portion of L to $500\,\text{cm}^3$ with distilled water in apparatus B. The resulting solution is M. The student then transfers $25.0\,\text{cm}^3$ of M into a conical flask and adds two drops of methyl orange indicator. Solution R is $0.100\,\text{mol dm}^{-3}$ aqueous sodium hydroxide, $\text{NaOH(aq)}$. R is delivered from a burette into the conical flask until the indicator alters colour and the end-point is reached.

Oct/Nov 2020

A student is given solution K, which is aqueous sodium hydroxide, NaOH, and the concentration of K is found by titration.

Oct/Nov 2020

During a titration, $25.0\,\text{cm}^3$ of aqueous sodium hydroxide is placed in a conical flask. Several drops of indicator are then introduced. Dilute hydrochloric acid is afterwards added to the flask until the end-point is reached. Which apparatus pieces are used to measure volume in this experiment?

Oct/Nov 2021

A student works out the percentage by mass of iron present in a sample of impure iron.

Oct/Nov 2021

The mixture is a solid made from iron(II) sulfate and sand. A student finds the percentage by mass of iron(II) sulfate in this mixture.

Oct/Nov 2021

When dilute sulfuric acid receives aqueous sodium hydroxide, the reaction takes place. $2\text{NaOH(aq)} + \text{H}_2\text{SO}_4\text{(aq)} \rightarrow \text{Na}_2\text{SO}_4\text{(aq)} + 2\text{H}_2\text{O(l)}$

Oct/Nov 2021

$4.0\,\text{g}$ of sodium hydroxide, $\text{NaOH}$, is added to $250\,\text{cm}^3$ of water in a graduated flask. A $25\,\text{cm}^3$ portion of this solution is then titrated using $0.50\,\text{mol dm}^{-3}$ hydrochloric acid. What volume of hydrochloric acid is needed to neutralise the alkali exactly?

Oct/Nov 2022

Solution K is an aqueous sodium hydroxide, $\text{NaOH}$, solution. A student finds the concentration of solution K by titration.

Oct/Nov 2022

Solution K is dilute sulfuric acid, $\text{H}_2\text{SO}_4$. A student uses titration to find the concentration of solution K.

Oct/Nov 2022

Aqueous calcium hydroxide reacts with dilute ethanoic acid. $2\text{CH}_3\text{COOH} + \text{Ca(OH)}_2 \rightarrow (\text{CH}_3\text{COO})_2\text{Ca} + 2\text{H}_2\text{O}$ A learner reacts $25.0\,\text{cm}^3$ of $0.0100\,\text{mol dm}^{-3}$ aqueous calcium hydroxide with dilute ethanoic acid, using thymolphthalein as the indicator. Exactly $12.5\,\text{cm}^3$ of dilute ethanoic acid reacts with the $0.0100\,\text{mol dm}^{-3}$ aqueous calcium hydroxide. Calculate the concentration, in $\text{mol dm}^{-3}$, of the dilute ethanoic acid.

Oct/Nov 2023

A student carries out a titration of aqueous sodium hydroxide using $0.1\,\text{mol dm}^{-3}$ hydrochloric acid. The results from the titration are then used to work out the concentration of the aqueous sodium hydroxide. Which row is correct?

Oct/Nov 2024

During a titration, a $25.0\,\text{cm}^3$ portion of $0.100\,\text{mol dm}^{-3}$ sodium hydroxide is neutralised exactly by $16.2\,\text{cm}^3$ of dilute sulfuric acid. The reaction equation is given below. $\text{H}_2\text{SO}_4 + 2\text{NaOH} \rightarrow \text{Na}_2\text{SO}_4 + 2\text{H}_2\text{O}$ Calculate the concentration of the dilute sulfuric acid.

Oct/Nov 2024

A learner carries out titrations on four samples of $0.800\,\text{mol dm}^{-3}$ aqueous sodium hydroxide, $\text{NaOH(aq)}$, using aqueous ethanedioic acid. For titration 1, the learner: • rinses a burette and then fills it with aqueous ethanedioic acid • uses a volumetric pipette to transfer $25.0\,\text{cm}^3$ of $\text{NaOH(aq)}$ into a conical flask • adds thymolphthalein indicator to the conical flask • sets the conical flask on a white tile • runs aqueous ethanedioic acid from the burette while swirling the flask, then adds it drop by drop close to the end-point until the solution has just changed colour. The learner carries out the titration three further times.

Oct/Nov 2024

A student carries out titrations on four separate aqueous sodium carbonate samples using $0.500\,\text{mol dm}^{-3}$ dilute hydrochloric acid, $\text{HCl(aq)}$.

Oct/Nov 2024

Which apparatus is used to measure the volume of acid needed to neutralise $25.0\,\text{cm}^3$ of alkali during a titration?

Oct/Nov 2025

A student explores the temperature changes that occur when an acid neutralises aqueous sodium hydroxide. The ionic equation for the reaction is shown: $\mathrm{H^+ + OH^- \rightarrow H_2O}$. This reaction releases heat. The temperature change is used to work out the concentration of hydrogen ions in an acid. X is $1.60\,\mathrm{mol/dm^3}$ sodium hydroxide solution. Y is an acid with concentration $2.00\,\mathrm{mol/dm^3}$. The student: step 1 fills the burette with Y; step 2 places a plastic cup inside a beaker; step 3 uses a volumetric pipette to add $25.0\,\mathrm{cm^3}$ of X to the plastic cup; step 4 measures the starting temperature of X and writes it in Table 2.1; step 5 adds $5.0\,\mathrm{cm^3}$ of Y from the burette to the plastic cup; step 6 stirs the mixture for 30 seconds and records the mixture temperature in Table 2.1; step 7 repeats steps 5 and 6 until a total of $40.0\,\mathrm{cm^3}$ of Y has been added. Fig. 2.1 shows two thermometer readings in ^{\circ}C during the investigation.

Oct/Nov 2025

A learner examines how temperature changes when an acid neutralises aqueous potassium hydroxide. The ionic equation for the reaction is shown: $\mathrm{H^+ + OH^- \rightarrow H_2O}$. This reaction releases heat. The temperature change is then used to find the concentration of hydrogen ions in an acid. X is an acid with concentration 0.80 mol/dm^3. Y is 2.0 mol/dm^3 potassium hydroxide. The learner: step 1 fills the burette with Y; step 2 places a plastic cup inside a beaker; step 3 uses a volumetric pipette to transfer 25.0 cm^3 of X into the plastic cup; step 4 measures the starting temperature of X and writes it in Table 2.1; step 5 adds 5.0 cm^3 of Y from the burette to the plastic cup; step 6 stirs the mixture for 30 seconds and enters the mixture temperature in Table 2.1; step 7 repeats steps 5 and 6 until a total of 40.0 cm^3 of Y has been added. Fig. 2.1 on page 6 shows two thermometer readings in ^{\circ}C from the experiment.

Oct/Nov 2025