R3.1 Proton transfer reactions questions for IB Chemistry

188 questions on Proton transfer reactions, written by Augment in the style of IB exam papers. Six of them are below in full, to answer on paper.

IB Chemistry
Part of R3 What are the mechanisms of chemical change?
SL and HL

Questions by paper and level

SL and HL questions are for students at either level. HL only questions cover what only HL students study.

Paper	SL and HL	HL only	All
Paper 1A	37	38	75
Paper 1B	25	11	36
Paper 2	43	34	77
Every paper	105	83	188

Counted on 10 November 2026

Questions to try

Written by Augment in the style of IB exams, not past papers. Answer them on paper, then check each one against its markscheme with a free account.

Question 1 · CHEM-00363Paper 1A · 1 mark

Dilute nitric acid is neutralized by dilute potassium hydroxide solution in a polystyrene cup. The thermometer reading rises from 21.0 °C to 27.5 °C.

Which statement is correct?

A
ΔH is positive because the temperature increases.
B
Heat is transferred from the surroundings to the reacting system.
C
ΔH is negative and the enthalpy of the products is lower than that of the reactants.
D
ΔH is negative and the reacting system gains energy.

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Question 2 · CHEM-00813Paper 1B · 10 marks

A student tested Hess's law by reacting solid sodium hydroxide with hydrochloric acid by two routes.

Route 1: 2.00 g of NaOH(s) was added to 100.0 cm³ of 0.500 mol dm⁻³ HCl(aq).
Route 2, step (i): 2.00 g of NaOH(s) was dissolved in 50.0 cm³ of water.
Route 2, step (ii): after the solution from step (i) had cooled to room temperature, 50.0 cm³ of 1.00 mol dm⁻³ HCl(aq) at the same temperature was added.

	Route 1	Route 2 (i)	Route 2 (ii)
Total volume of solution / cm³	100.0	50.0	100.0
Temperature rise / °C ± 0.2 °C	11.6	10.1	6.5

Assume all solutions have a density of 1.00 g cm⁻³ and the specific heat capacity of water.

(a)
Write the equation for the reaction in Route 1, including state symbols.
1 mark
(b)
Calculate the enthalpy change, in kJ mol⁻¹, for Route 1.
2 marks
(c)
Calculate the total enthalpy change, in kJ mol⁻¹, for Route 2.
2 marks
(d)
The percentage uncertainty in the enthalpy change for Route 1 is about 2 %. Evaluate whether the results support Hess's law.
2 marks
(e)
Explain why the solution from step (i) was allowed to cool before step (ii).
1 mark
(f)
Solid sodium hydroxide absorbs water and carbon dioxide from the air. State the effect of this on the measured enthalpy changes.
1 mark
(g)
State one safety precaution needed when handling solid sodium hydroxide.
1 mark

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Question 3 · CHEM-00282Paper 2 · 9 marks

Ammonia, NH₃, is manufactured by the Haber process. It is a gas at room temperature and is very soluble in water.

(a)
Draw the Lewis (electron dot) formula of ammonia.
1 mark
(b)
State the molecular geometry of ammonia and predict its H–N–H bond angle.
2 marks
(c)
Explain why the H–N–H bond angle in ammonia is smaller than the H–C–H bond angle in methane, CH₄.
2 marks
(d)(i)
Ammonia reacts with hydrogen chloride to form ammonium chloride, NH₄Cl. Outline how the coordination bond in the ammonium ion, NH₄⁺, forms.
1 mark
(d)(ii)
State the H–N–H bond angle in the ammonium ion.
1 mark
(e)
Explain why ammonia is very soluble in water.
2 marks

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Question 4 · CHEM-00666Paper 1A · 1 mark

Each of the oxides is added to separate samples of water. Which list shows the resulting solutions in order of increasing pH?

A
CO₂ < SO₃ < MgO < Na₂O
B
SO₃ < CO₂ < MgO < Na₂O
C
SO₃ < CO₂ < Na₂O < MgO
D
Na₂O < MgO < CO₂ < SO₃

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Question 5 · CHEM-00986Paper 1B · 9 marks

The value of x in a sample of washing soda crystals, Na₂CO₃·xH₂O, was found by titration.

3.575 g of the crystals was dissolved in distilled water and made up to 250.0 cm³ in a volumetric flask. 25.00 cm³ portions were titrated with 0.1000 mol dm⁻³ hydrochloric acid using methyl orange indicator.

N a_{2} C O_{3} (a q) + 2 H C l (a q) \to 2 N a C l (a q) + H_{2} O (l) + C O_{2} (g)

Titration	Rough	1	2	3
Final burette reading / cm³ ± 0.05 cm³	25.90	25.95	25.70	26.45
Initial burette reading / cm³ ± 0.05 cm³	0.00	0.50	0.20	1.05

(a)
Calculate the mean titre, stating which results you have used.
2 marks
(b)
State the absolute uncertainty in each titre and calculate the percentage uncertainty in the mean titre.
1 mark
(c)
Calculate the amount, in mol, of sodium carbonate in the 250.0 cm³ solution.
2 marks
(d)
Determine the value of x.
2 marks
(e)
The formula of fresh washing soda is Na₂CO₃·10H₂O. Suggest a reason for the value of x obtained.
1 mark
(f)
Outline why it is not necessary to dry the conical flask before each titration, but the pipette must be rinsed with the sodium carbonate solution.
1 mark

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Question 6 · CHEM-00432Paper 2 · 8 marks

A small piece of sodium is dropped into a trough of water to which a few drops of phenolphthalein indicator have been added.

(a)
Write the equation for the reaction, including state symbols.
2 marks
(b)
Describe two observations, other than a colour change, made during the reaction.
2 marks
(c)
Explain why the solution turns pink.
1 mark
(d)
Explain why potassium reacts more vigorously with water than sodium.
2 marks
(e)
Suggest why lithium, sodium and potassium are stored under oil.
1 mark

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