Lesson 12.3.2

12.3.2 Buffer solutions Quiz: Pearson Edexcel Chemistry, Unit 12

20 questions

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Lesson 12.3.2, Buffer solutions: 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 a buffer solution?

    • A solution in which the pH changes by the same amount for every addition of acid
    • A solution whose pH is exactly 7 at 298 K whatever is dissolved in it
    • A solution that resists a change in pH when small amounts of acid or alkali are added
    • A solution containing only a strong acid and its salt in equal amounts

  2. Which pair of substances makes an acidic buffer?

    • A weak acid together with its conjugate base, such as ethanoic acid and sodium ethanoate
    • Two strong acids of different concentrations, mixed in equal volumes to give a solution of mixed pH
    • A weak base together with a strong acid in large excess, so that the weak base is fully protonated
    • A strong acid together with a strong base in equal moles, which gives a neutral salt solution at equivalence

  3. What happens when a small amount of H+ ions is added to an ethanoic acid and sodium ethanoate buffer?

    • The added H+ ions react with water to form OH- ions which neutralise them
    • The sodium ions absorb the H+ ions so the pH remains constant
    • The ethanoic acid reacts with H+ to form more H+ ions
    • The ethanoate ions react with the added H+ ions to form ethanoic acid

  4. What happens when a small amount of OH- ions is added to an ethanoic acid and sodium ethanoate buffer?

    • The OH- ions combine with sodium ions to form a precipitate
    • The ethanoate ions react with OH- ions to release H+ ions
    • The ethanoic acid reacts with the OH- ions to form ethanoate ions and water
    • The salt is hydrolysed, adding more OH- ions to the solution

  5. Which salt would be used with ethanoic acid to make a buffer?

    • Sodium chloride
    • Sodium ethanoate
    • Sodium hydroxide
    • Sodium nitrate

  6. Why must a buffer contain both a weak acid and its conjugate base rather than the weak acid alone?

    • The conjugate base is needed to make the solution more concentrated and so more acidic
    • Only the conjugate base can remove added H+ ions, while only the weak acid can remove added OH- ions
    • A weak acid alone is fully dissociated, so the pH cannot be controlled
    • The weak acid alone reacts with water to form a salt that buffers the solution

  7. In an ammonia buffer, which species removes added H+ ions?

    • Water molecules, which release OH- to neutralise the acid
    • Ammonium ions, which donate H+ to form more NH3
    • Ammonia, NH3, which accepts H+ to form NH4+
    • Chloride ions, which accept H+ to form hydrogen chloride

  8. Which expression gives the pH of an acidic buffer?

    • pH = pKa x [A-] / [HA]
    • pH = pKa - log10([A-] / [HA])
    • pH = 14 - pKa + log10([A-] / [HA])
    • pH = pKa + log10([A-] / [HA])

  9. A buffer contains 0.20 mol dm-3 HA and 0.10 mol dm-3 A- with Ka = 1.8 x 10^-5 mol dm-3. What is its pH?

    • 5.44
    • 3.44
    • 4.44
    • 4.74

  10. What is the pH of a buffer with equal concentrations of a weak acid and its salt, where the acid has pKa 4.76?

    • 9.52
    • 4.76
    • 2.38
    • 7.00

  11. A buffer must have pH 5.00 with pKa 4.76. What is the required ratio [A-]/[HA]?

    • 5.00
    • 10.0
    • 0.57
    • 1.74

  12. How many moles of sodium ethanoate must be added to 100 cm3 of 0.10 mol dm-3 ethanoic acid to make a buffer of pH 5.00 (pKa 4.76), assuming no volume change?

    • 0.0174 mol
    • 0.0100 mol
    • 0.0240 mol
    • 0.00574 mol

  13. Which species neutralises added OH- ions in an ethanoic acid and sodium ethanoate buffer?

    • Sodium ions, which react with OH- to form sodium hydroxide
    • Ethanoic acid, CH3COOH, which reacts with OH- to form ethanoate and water
    • Ethanoate ions, which react with OH- to release H+ ions
    • Water molecules, which accept OH- ions to form stable hydroxide complexes

  14. Which change increases the buffer capacity of a buffer while keeping the pH the same?

    • Increasing the concentrations of both the weak acid and its salt in the same ratio
    • Replacing the weak acid with a strong acid of the same concentration
    • Adding more strong acid until the ratio of salt to acid changes
    • Diluting the buffer with water while keeping the ratio the same

  15. A buffer has 0.10 mol HA and 0.10 mol A- in 1.0 dm3 (pKa 4.76). If 0.010 mol NaOH is added, what is the new pH?

    • 4.67
    • 9.13
    • 4.76
    • 4.85

  16. A buffer is made by mixing 40.0 cm3 of 0.200 mol dm-3 ethanoic acid with 10.0 cm3 of 0.200 mol dm-3 NaOH (pKa 4.76). What is the pH of the buffer?

    • 3.76
    • 4.76
    • 4.28
    • 5.24

  17. A student says the pH of a buffer does not change on dilution. Which evaluation is best?

    • The pH rises to 7 because the buffer is diluted and the acid is neutralised by water
    • The pH falls on dilution because more of the acid dissociates to reduce the ratio
    • The pH is exactly unchanged and the buffer capacity increases on dilution
    • The pH stays almost the same

  18. The most effective buffer range is about pKa plus or minus 1 pH unit. What is the effective range for a buffer with pKa 4.76?

    • About pH 0.8 to 2.8
    • About pH 3.8 to 5.8
    • About pH 6.8 to 8.8
    • About pH 4.2 to 4.4

  19. What is the pH of a buffer made from equal concentrations of ammonia and ammonium chloride, given that the pKa of NH4+ is 9.25?

    • 7.00
    • 11.10
    • 9.25
    • 4.75

  20. Why does a mixture of hydrochloric acid and sodium chloride not act as a buffer?

    • Chloride ions are the conjugate base of a strong acid and do not react with added H+
    • Hydrochloric acid has pH 7, so it is already neutral and cannot respond to added acid
    • Sodium ions neutralise added OH- ions, so the pH stays constant regardless of the acid
    • Chloride ions are a strong base that react with added H+ to form hydrogen chloride gas

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