Lesson 12.4.1

12.4.1 Enthalpy of neutralisation and carbonic acid buffering Quiz: Pearson Edexcel Chemistry, Unit 12

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 12.4.1, Enthalpy of neutralisation and carbonic acid buffering: 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 enthalpy of neutralisation?

    • The enthalpy change when one mole of a salt dissolves in water to give a solution at 298 K
    • The enthalpy change when one mole of acid reacts completely with any mass of base
    • The enthalpy change when one mole of water is formed from an acid and an alkali under standard conditions
    • The energy needed to break one mole of O-H bonds in liquid water at 298 K and 100 kPa

  2. What is the typical enthalpy of neutralisation for a strong acid reacting with a strong alkali?

    • About +57 kJ mol-1
    • About -114 kJ mol-1
    • About -10 kJ mol-1
    • About -57 kJ mol-1

  3. Why is the enthalpy of neutralisation of a weak acid less exothermic than that of a strong acid?

    • Weak acids do not react with alkalis, so the enthalpy change is much smaller
    • Some energy is absorbed to dissociate the weak acid completely, so less heat is released
    • The weak acid releases more energy on dissociation, making the reaction more exothermic
    • The water formed from a weak acid has a lower enthalpy of formation

  4. Which species form the carbonic acid-hydrogencarbonate buffer in blood?

    • H2CO3 (carbonic acid) and HCO3- (hydrogencarbonate) ions
    • Sodium and chloride ions, which are the spectator ions in a neutral salt solution
    • Dissolved CO2 and O2 gas molecules, which are exchanged in the lungs only
    • Hydronium and hydroxide ions, which combine to form water in a strong acid-base reaction

  5. What is the normal pH range of human blood?

    • About 7.35 to 7.45
    • About 5.00 to 5.50
    • About 6.00 to 6.50
    • About 8.00 to 8.50

  6. How does the hydrogencarbonate ion respond when H+ ions are added to blood?

    • HCO3- reacts with H+ to form H2CO3, which can decompose to CO2 and water
    • H2CO3 releases more H+ ions, which lowers the pH further
    • HCO3- reacts with H+ to form carbonate ions which are removed as a gas
    • OH- ions are produced that remove the added H+ ions from the blood

  7. Which equation shows how carbonic acid is linked to CO2 removal in the lungs?

    • H+ + OH- gives H2O + 2CO2
    • CO2 + 2OH- gives CO3 2- + H2O
    • H2CO3 gives H2 + CO3
    • H2CO3 gives CO2 + H2O

  8. A reaction of 50.0 cm3 of 1.0 mol dm-3 HCl with 50.0 cm3 of 1.0 mol dm-3 NaOH gives a temperature rise of 6.8 C. Using c = 4.18 J g-1 K-1 and 100 g of solution, what is the enthalpy of neutralisation?

    • +57 kJ mol-1
    • -57 kJ mol-1
    • -2.8 kJ mol-1
    • -114 kJ mol-1

  9. If the ratio [HCO3-]/[H2CO3] in blood is 20:1 and the apparent pKa is 6.1, what is the blood pH?

    • 7.00
    • 8.10
    • 6.10
    • 7.40

  10. If the ratio [HCO3-]/[H2CO3] falls from 20:1 to 10:1, which statement is correct?

    • The pH falls by about 0.3 units to about 7.10, which is a move towards acidosis
    • The pH rises by about 0.3 units to about 7.70, which is a move towards alkalosis
    • The pH falls by about 3 units to about 4.10 because the buffer is exhausted
    • The pH stays at 7.40 because the ratio is fixed in blood

  11. Which enthalpy of neutralisation comparison is correct?

    • The weak acid gives a more exothermic value because it releases more energy when ionising
    • Both give identical values because both release H+ ions in water
    • The strong acid gives a more exothermic value because no energy is needed to ionise it
    • The weak acid gives a positive value because weak acids absorb heat as they react

  12. What is log10(20) to two decimal places?

    • 0.30
    • 1.30
    • 2.00
    • 1.00

  13. When breathing removes CO2 from the blood, what happens to the concentration of H2CO3 and the pH?

    • H2CO3 rises because CO2 leaves the blood, so the pH falls
    • H2CO3 is unaffected because it is a strong acid
    • H2CO3 falls because CO2 leaves, shifting the equilibrium so the pH rises
    • H2CO3 rises because CO2 is absorbed into water, so the pH falls

  14. What happens to blood pH during hyperventilation, when a person breathes out too much CO2?

    • The pH does not change because CO2 is not dissolved in blood
    • The pH falls, causing acidosis
    • The pH falls below 6.0 at once because hydrogen ions accumulate
    • The pH rises, causing alkalosis

  15. What ratio [HCO3-]/[H2CO3] gives a blood pH of 7.40, using an apparent pKa of 6.1?

    • 20:1
    • 10:1
    • 1:20
    • 2:1

  16. The enthalpy of neutralisation of a weak acid with NaOH is -55 kJ mol-1, and that of a strong acid is -57 kJ mol-1. What is the implied enthalpy change for dissociating the weak acid?

    • +2 kJ mol-1
    • +55 kJ mol-1
    • -2 kJ mol-1
    • +112 kJ mol-1

  17. A student says the blood buffer works because its ratio is 1:1 and gives pH 7.40. Which evaluation is best?

    • Incorrect, because the blood buffer contains no carbonate or hydrogencarbonate species
    • Incorrect, because the blood ratio is about 20:1, and a 1:1 ratio would give pH near the apparent pKa of 6.1
    • Correct, because a 1:1 ratio always gives pH 7.40 in biological systems
    • Correct, because any ratio gives the same pH, so the buffer is effective at all concentrations

  18. A 25.0 cm3 sample of 1.00 mol dm-3 HCl is neutralised by excess NaOH. The solution has mass 50.0 g, a temperature rise of 5.0 C and c = 4.18 J g-1 K-1. What is the enthalpy of neutralisation?

    • +41.8 kJ mol-1
    • -4.2 kJ mol-1
    • -41.8 kJ mol-1
    • -83.6 kJ mol-1

  19. Why does the blood buffer rely on the lungs and kidneys as well as the carbonic acid buffer?

    • The lungs add H+ ions and the kidneys remove OH- ions to keep the pH constant
    • The lungs and kidneys both produce carbonic acid, which is the main buffer
    • The lungs remove CO2 and the kidneys regenerate hydrogencarbonate
    • The kidneys remove CO2 while the lungs regenerate hydrogencarbonate ions

  20. Which statement about the carbonic acid buffer is correct?

    • It is equally effective across all pH values because it contains two acids
    • It is most effective within about 1 pH unit of its pKa of about 6.1
    • It is most effective at exactly pH 7.40 because that is its pKa
    • It is most effective only at pH below 2 because carbonic acid is a strong acid

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