S2.2 The covalent model questions for IB Chemistry

242 questions on The covalent model, 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 S2 Models of bonding and structure
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	69	32	101
Paper 1B	24	4	28
Paper 2	72	41	113
Every paper	165	77	242

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-00004Paper 1A · 1 mark

Which gas would deviate most from ideal behaviour at 300 K and 100 kPa?

A
$N H_{3}$
B
$N_{2}$
C
$H_{2}$
D
$H e$

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Question 2 · CHEM-01003Paper 1B · 11 marks

A student investigated the cooling caused by the evaporation of four alcohols. A small square of filter paper was wrapped around the tip of a temperature probe and soaked in an alcohol at room temperature, 21.4 °C. The probe was clamped in air and the lowest temperature reached within 120 s was recorded. Each alcohol was tested three times.

Alcohol	Formula	ΔT trial 1 / °C	ΔT trial 2 / °C	ΔT trial 3 / °C	Mean ΔT / °C
methanol	$C H_{3} O H$	13.6	13.1	13.8	13.5
ethanol	$C_{2} H_{5} O H$	10.4	9.7	10.1	10.1
propan-1-ol	$C_{3} H_{7} O H$	5.3	5.0	4.4
butan-1-ol	$C_{4} H_{9} O H$	2.5	2.1	2.3	2.3

Each temperature reading has an uncertainty of ± 0.1 °C.

(a)
Identify the independent and dependent variables.
1 mark
(b)
State two variables that should be controlled.
2 marks
(c)
Calculate the mean ΔT for propan-1-ol.
1 mark
(d)
Explain, using the kinetic molecular theory, why the temperature of the probe falls as the alcohol evaporates.
2 marks
(e)
Explain the trend in the mean ΔT values.
2 marks
(f)
Calculate the percentage uncertainty in the mean ΔT for butan-1-ol.
1 mark
(g)
Comment on the precision of the butan-1-ol result compared with the methanol result.
1 mark
(h)
Suggest one modification that would reduce the percentage uncertainty in ΔT for butan-1-ol.
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-00038Paper 1A · 1 mark

Why does the boiling point of the straight-chain alkanes increase from butane to hexane?

A
More covalent bonds must be broken as the chain gets longer.
B
Hydrogen bonding between molecules becomes stronger.
C
The molecules become more polar, so dipole–dipole forces increase.
D
The London (dispersion) forces between molecules become stronger.

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Question 5 · CHEM-01005Paper 1B · 11 marks

100.0 cm³ of a solution containing 12.0 cm³ of ethanol in water was fractionally distilled. The temperature at the top of the column was recorded as the distillate was collected in a measuring cylinder. The boiling point of pure ethanol is 78.4 °C.

Volume of distillate / cm³ ± 0.5 cm³	Temperature / °C ± 0.5 °C
2.0	78.5
4.0	78.5
6.0	79.0
8.0	80.0
10.0	83.5
12.0	90.0
14.0	96.5
16.0	99.5
18.0	100.0
20.0	100.0

(a)
Identify the substance that makes up most of the first 6 cm³ of distillate.
1 mark
(b)
Comment on whether the first readings agree with the boiling point of pure ethanol.
2 marks
(c)
Explain why the temperature rises between 8 cm³ and 16 cm³ of distillate.
2 marks
(d)
The distillate collected below 82 °C was kept as the first fraction. Estimate its volume from the data.
1 mark
(e)
Assuming the first fraction is pure ethanol, calculate the percentage of the ethanol that was recovered in it, and suggest one reason why it is less than 100 %.
2 marks
(f)
State where the thermometer bulb must be placed, and why.
1 mark
(g)
Suggest one way of testing the purity of the first fraction.
1 mark
(h)
State one safety precaution needed in this experiment.
1 mark

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Question 6 · CHEM-00283Paper 2 · 8 marks

Hydrogen cyanide, HCN, is a highly toxic liquid used in the manufacture of some polymers. Its boiling point is 26 °C.

(a)
Draw the Lewis (electron dot) formula of hydrogen cyanide.
1 mark
(b)
State the molecular geometry of hydrogen cyanide and its H–C–N bond angle.
2 marks
(c)(i)
Using section 11 of the data booklet, state the length of the carbon–nitrogen bond in HCN and of the carbon–nitrogen bond in methylamine, CH₃NH₂.
1 mark
(c)(ii)
Explain why the carbon–nitrogen bond in HCN is shorter and stronger than the one in methylamine.
2 marks
(d)
Using section 9 of the data booklet, deduce whether a molecule of HCN is polar.
2 marks

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