Lesson 3.1.12.5

3.1.12.5 pH curves, titrations and indicators Quiz: AQA Chemistry, Unit 1

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.1.12.5, pH curves, titrations and indicators: 20 multiple choice questions for the AQA Chemistry (7405), Unit 1: Physical chemistry, written with Revision Ninja.

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The 20 questions

  1. What is the pH at the equivalence point of a strong acid titrated with a strong base?

    • Greater than 7, because the salt formed is basic
    • 7
    • Less than 7, because the salt formed is acidic
    • Exactly 1, because the strong acid remains

  2. What is the pH at the equivalence point of a weak acid titrated with a strong base?

    • Less than 7, because the weak acid is still present
    • Exactly 7, because all titrations give pH 7
    • Greater than 7, because the salt formed is basic
    • Exactly 1, because only the acid is in the flask

  3. What is the pH at the equivalence point of a strong acid titrated with a weak base such as ammonia?

    • Exactly 14, because ammonia is a base
    • Greater than 7, because the salt formed is basic
    • Exactly 7, because all titrations give pH 7
    • Less than 7, because the salt formed is acidic

  4. What is a vertical section of a pH curve?

    • A region where the pH stays almost constant as acid is added
    • A rapid change in pH around the equivalence point
    • The pH at which the indicator changes colour at the start
    • The starting pH of the solution before any titrant is added

  5. What is the best indicator for titrating a weak acid with a strong base?

    • Bromothymol blue, whose range lies entirely below pH 4 for every titration
    • Phenolphthalein, whose colour change range of about 8.2 to 10 lies on the steep part of the curve
    • Any indicator, because the pH curve is the same for all acids and bases
    • Methyl orange, whose colour change range of about 3.1 to 4.4 lies on the steep part of the curve

  6. Which indicator is most suitable for titrating a strong acid with a weak base such as ammonia?

    • Phenolphthalein, because phenolphthalein changes colour in strong acid only
    • Any indicator, because the pH of the equivalence point is always 14
    • Methyl orange, whose colour change range of about 3.1 to 4.4 matches the acidic equivalence point
    • Phenolphthalein, whose colour change range of about 8.2 to 10 matches the acidic equivalence point

  7. 25.0 cm^3 of 0.100 mol dm^-3 NaOH is titrated with 0.0500 mol dm^-3 HCl. What volume of HCl is needed to reach the equivalence point?

    • 50.0 cm^3
    • 100 cm^3
    • 25.0 cm^3
    • 12.5 cm^3

  8. 20.0 cm^3 of 0.200 mol dm^-3 HCl is neutralised by 0.100 mol dm^-3 NaOH. What volume of NaOH is needed?

    • 40.0 cm^3
    • 80.0 cm^3
    • 10.0 cm^3
    • 20.0 cm^3

  9. 25.0 cm^3 of ethanoic acid is titrated with 0.100 mol dm^-3 NaOH, and 22.5 cm^3 is needed to reach the equivalence point. What is the concentration of the acid?

    • 0.100 mol dm^-3
    • 0.0900 mol dm^-3
    • 0.0450 mol dm^-3
    • 0.225 mol dm^-3

  10. What is the pH of a 0.10 mol dm^-3 strong acid at the start of its titration with a strong base?

    • 0.10
    • 13.0
    • 1.0
    • 7.0

  11. Why does a weak acid titration curve start at a higher pH than a strong acid of the same concentration?

    • The weak acid contains more H+ ions than the strong acid at the same concentration
    • The weak acid has a higher concentration of OH- ions at the start
    • The weak acid does not dissociate at all, so its pH is the same as pure water
    • The weak acid is only partly dissociated, so it has a lower [H+] at the start

  12. Why does the pH at the equivalence point of a weak acid titration not equal 7?

    • The salt formed is strongly acidic, because weak acids always produce acidic salts
    • The salt formed hydrolyses to give an excess of OH^- ions, so the solution is basic
    • Water is consumed completely in the reaction, leaving no solvent to set the pH
    • The equivalence point is always at pH 14, whatever the acid used

  13. A monoprotic acid solution of 25.0 cm^3 requires 20.0 cm^3 of 0.0250 mol dm^-3 NaOH to reach the equivalence point. What is the concentration of the acid?

    • 0.0250 mol dm^-3
    • 0.0400 mol dm^-3
    • 0.0100 mol dm^-3
    • 0.0200 mol dm^-3

  14. What volume of 0.10 mol dm^-3 NaOH neutralises 10.0 cm^3 of 0.050 mol dm^-3 nitric acid?

    • 20.0 cm^3
    • 10.0 cm^3
    • 2.5 cm^3
    • 5.0 cm^3

  15. Why does a strong acid and strong base curve show a larger pH change at the equivalence point than a weak acid and strong base curve?

    • The strong acid is fully dissociated, so the pH changes more sharply near the equivalence point
    • The weak acid has a higher concentration of H+ ions, which buffers the pH change
    • The weak acid is fully dissociated, so the pH changes more sharply near the equivalence point
    • The strong base is only partly dissociated, so the pH changes less sharply

  16. Which statement about the choice of indicator in a titration is correct?

    • An indicator should change colour within the steep vertical part of the pH curve at the equivalence point
    • An indicator should change colour at pH 7 in every titration, whatever the acid and base
    • An indicator should change colour at the very start of the titration, before any reagent is added
    • An indicator should be a strong acid, so that it dissociates fully in the flask

  17. Which combination of acid and base gives an equivalence point at pH 7?

    • Ethanoic acid and sodium hydroxide
    • Ethanoic acid and ammonia
    • Hydrochloric acid and ammonia
    • Hydrochloric acid and sodium hydroxide

  18. What is the purpose of a pH curve in an acid-base titration?

    • To show how pH changes as titrant is added, so that a suitable indicator can be chosen
    • To show the number of electrons transferred during the titration
    • To show the rate at which the acid and base react with each other
    • To show the enthalpy change of the neutralisation reaction at each point

  19. On the pH curve of a weak acid titrated with a strong base, where is the half-equivalence point?

    • At the start of the titration, where the pH equals 7, before any of the titrant has been added to the flask
    • At half the volume needed to reach the equivalence point, where pH equals pKa of the weak acid
    • At the equivalence point itself, where the pH equals 14, because the weak acid has been fully neutralised by base
    • At twice the volume of the equivalence point, where the pH equals 1, because excess strong acid is then present

  20. Where is the equivalence point located on a pH curve?

    • At the flat region at the top of the curve, where pH stays constant
    • At the very start of the curve, before any titrant is added
    • At the centre of the steep vertical section, where moles of acid and base are equal
    • At the end of the curve, when all the titrant has been used up

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