Lesson 12.3.1

12.3.1 Titration curves and indicators Quiz: Pearson Edexcel Chemistry, Unit 12

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 12.3.1, Titration curves and indicators: 20 multiple choice questions for the Pearson Edexcel Chemistry (9CH0), Unit 12: Acid-base Equilibria, 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 at 298 K?

    • 7.00, because the salt formed is neutral
    • Above 10, because the base remains in excess
    • Below 4, because the acid remains in excess
    • About 5, because water is partly dissociated

  2. Why is the equivalence point of a weak acid titrated with a strong base above pH 7?

    • The solution is buffered at exactly pH 7 because both species are present
    • Strong bases always give a solution with pH above 10 at equivalence
    • The conjugate base of the weak acid is hydrolysed, producing excess OH- ions
    • The weak acid is stronger than the base at equivalence, leaving excess H+ ions

  3. Why is the equivalence point of a strong acid titrated with a weak base below pH 7?

    • The weak base remains in excess, making the solution basic
    • Strong acids and weak bases always neutralise to exactly pH 7
    • The salt formed is hydrolysed, producing H+ ions
    • The indicator is protonated, so the solution is strongly basic

  4. What property must an indicator have to be suitable for a titration?

    • Its colour change must be at exactly pH 7 for every titration
    • It must be colourless in both acid and base so that no change is seen
    • It must be used at a pH far below the equivalence point to act quickly
    • Its colour change must occur within the steep vertical section of the titration curve

  5. At the half-equivalence point of a weak acid titrated with a strong base, which statement is true?

    • pH equals 7, because the solution is neutral
    • pH equals 14 minus pKa
    • pH equals pKa, because [HA] equals [A-]
    • pH equals the concentration of the base in mol dm-3

  6. What does the steep vertical section of a titration curve show?

    • A constant pH throughout, because the buffer resists every addition of titrant made before the equivalence point
    • The total moles of acid present in the flask
    • A large change in pH for a very small volume of titrant added near the equivalence point
    • A gradual, steady change in pH over the whole titration, with no sharp change at any single volume of titrant

  7. Why is it important for an indicator's colour change to fall within the steep section of a curve?

    • It means the indicator must change colour exactly at pH 7 in every titration
    • It means the end point is sharp, so the volume read at the colour change is close to the equivalence volume
    • It means the indicator avoids the buffer region, so the titration is always quicker
    • It means the indicator is strongly coloured only in the acid and colourless in the base

  8. A 25.0 cm3 sample of 0.100 mol dm-3 hydrochloric acid is titrated, and no sodium hydroxide has been added. What is its pH?

    • 2.00
    • 13.00
    • 0.10
    • 1.00

  9. What is the pH after 10.0 cm3 of 0.100 mol dm-3 NaOH is added to 25.0 cm3 of 0.100 mol dm-3 HCl?

    • 7.00
    • 4.30
    • 1.37
    • 1.00

  10. What is the approximate pH at the equivalence point when 0.100 mol dm-3 ethanoic acid (Ka = 1.7 x 10^-5 mol dm-3) is titrated with 0.100 mol dm-3 NaOH?

    • About 8.7
    • About 3.0
    • Exactly 7.00
    • About 5.3

  11. What volume of 0.100 mol dm-3 NaOH is needed to reach the equivalence point with 25.0 cm3 of 0.200 mol dm-3 HCl?

    • 12.5 cm3
    • 25.0 cm3
    • 50.0 cm3
    • 100 cm3

  12. A weak acid is titrated with NaOH. At the half-equivalence point the pH is 4.76. What is the pKa of the acid?

    • 4.76
    • 2.38
    • 7.00
    • 9.52

  13. Which indicator is most suitable for titrating 0.100 mol dm-3 ethanoic acid with NaOH, where the equivalence pH is about 8.7?

    • Methyl red, which changes colour over about pH 4.4 to 6.2
    • Methyl orange, which changes colour over about pH 3.1 to 4.4
    • Phenolphthalein, which changes colour over about pH 8.2 to 10
    • Bromothymol blue, which changes colour over about pH 6.0 to 7.6

  14. A student titrates a weak acid with NaOH using methyl orange, which changes colour between pH 3.1 and 4.4. What is the likely effect on the result?

    • The indicator does not change colour, so the titre cannot be measured
    • The colour change occurs after the equivalence point, so the titre is too large
    • The titre is accurate because methyl orange changes at the equivalence point of all acids
    • The colour change occurs well before the equivalence point, so the titre is too small

  15. What is the pH of 25.0 cm3 of 0.100 mol dm-3 ethanoic acid (Ka = 1.7 x 10^-5 mol dm-3) before any NaOH is added?

    • 2.88
    • 4.76
    • 1.00
    • 7.00

  16. Why does a weak acid-strong base titration curve rise more slowly at the start than a strong acid-strong base curve of the same concentrations?

    • The weak acid and its conjugate base together resist pH change, so the curve is flatter at the start
    • The weak acid releases more hydrogen ions than a strong acid, so the pH rises more slowly
    • The weak acid is fully dissociated, so the pH changes only at the equivalence point
    • The strong base reacts with water first, so no pH change occurs until the end

  17. A 0.100 mol dm-3 weak acid HA with Ka = 2.0 x 10^-5 mol dm-3 is titrated with 0.100 mol dm-3 NaOH; 25.0 cm3 of acid is used. What volume of NaOH gives the half-equivalence point?

    • 6.25 cm3
    • 12.5 cm3
    • 25.0 cm3
    • 50.0 cm3

  18. Two 0.100 mol dm-3 titrations are done with 25.0 cm3 of acid: one strong (HCl) and one weak monobasic (HA), both against 0.100 mol dm-3 NaOH. Which statement is correct?

    • Neither can be titrated accurately, because the equivalence point of a weak acid cannot be detected by any indicator
    • The weak acid needs twice as much NaOH because weak acids release two protons
    • The strong acid needs more NaOH because its ionisation releases fewer hydrogen ions than the weak acid does
    • Both need the same volume of NaOH to reach equivalence, but their equivalence point pH values differ

  19. What is the pH after 30.0 cm3 of 0.100 mol dm-3 NaOH is added to 25.0 cm3 of 0.100 mol dm-3 HCl?

    • 7.00
    • 11.96
    • 12.50
    • 2.04

  20. A teacher claims that any indicator changing colour near pH 7 will work for every titration. Which response is best?

    • Correct, because the equivalence point of every acid-base titration is pH 7, so any indicator changing near 7 will do
    • Incorrect, because the indicator must change colour within the steep section at the equivalence point, which is above pH 7 here
    • Incorrect, because indicators cannot be used reliably for any titration involving a weak acid or a weak base
    • Correct, because an indicator only needs a colour change somewhere in the broad range between pH 4 and pH 10 to work

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