S3.2 Functional groups: classification of organic compounds questions for IB Chemistry

264 questions on Functional groups: classification of organic compounds, 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 S3 Classification of matter
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	66	44	110
Paper 1B	23	9	32
Paper 2	68	54	122
Every paper	157	107	264

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-00021Paper 1A · 1 mark

What is the empirical formula of butane?

A
$C H_{2}$
B
$C_{2} H_{5}$
C
$C_{4} H_{10}$
D
$C H_{3} C H_{2} C H_{2} C H_{3}$

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Question 2 · CHEM-00512Paper 1B · 10 marks

A compound L, isolated from sour milk, contains carbon, hydrogen and oxygen only. 0.2000 g of L was burned completely in a stream of dry oxygen over hot copper(II) oxide. The gases produced passed first through tube A, containing anhydrous calcium chloride, which absorbs water, and then through tube B, containing soda lime, which absorbs carbon dioxide and water.

Tube	Mass before / g ± 0.0001 g	Mass after / g ± 0.0001 g
A (calcium chloride)	32.4160	32.5373
B (soda lime)	45.1082	45.4007

(a)
Calculate the mass of carbon in the sample.
1 mark
(b)
Calculate the mass of hydrogen in the sample.
1 mark
(c)
Determine the empirical formula of L.
2 marks
(d)
The molar mass of L is 90.1 g mol⁻¹. Deduce its molecular formula.
1 mark
(e)
Explain why tube A must be placed before tube B.
2 marks
(f)
Suggest the purpose of the hot copper(II) oxide.
1 mark
(g)
The mass of water collected is about 1 % higher than the value expected for the formula in (d). Suggest one reason for this.
1 mark
(h)
Predict the effect on the calculated C : H ratio if some carbon monoxide had passed through both tubes unabsorbed.
1 mark

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Question 3 · CHEM-00290Paper 2 · 9 marks

Methanal, HCHO, is used to make resins. It is a gas at room temperature (boiling point −19 °C) and dissolves readily in water. Methanol, CH₃OH, has a similar molar mass but boils at 65 °C.

(a)
Draw the Lewis (electron dot) formula of methanal.
1 mark
(b)
Predict the H–C–H bond angle in methanal and explain why it differs from the ideal trigonal planar angle.
2 marks
(c)
Identify the strongest type of intermolecular force between methanal molecules and explain why methanal molecules cannot form hydrogen bonds with each other.
2 marks
(d)
Explain why methanal dissolves readily in water.
2 marks
(e)
Explain why methanol has a much higher boiling point than methanal.
2 marks

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Question 4 · CHEM-00022Paper 1A · 1 mark

Which type of formula is $C H_{3} C H_{2} C H (O H) C H_{3}$ ?

A
Empirical formula
B
Molecular formula
C
Skeletal formula
D
Condensed structural formula

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Question 5 · 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 6 · CHEM-00291Paper 2 · 7 marks

Three structural isomers have the molecular formula C₅H₁₂.

Isomer	Structural formula	Boiling point / °C
pentane	$C H_{3} C H_{2} C H_{2} C H_{2} C H_{3}$	36
2-methylbutane	$C H_{3} C H (C H_{3}) C H_{2} C H_{3}$	28
2,2-dimethylpropane	$C (C H_{3})_{4}$	10

(a)
State the type of intermolecular force between molecules of these isomers.
1 mark
(b)
Explain the trend in boiling points shown in the table.
2 marks
(c)
Predict, giving a reason, whether 2,2-dimethylbutane, $(C H_{3})_{3} C C H_{2} C H_{3}$ , has a higher or lower boiling point than hexane, $C H_{3} (C H_{2})_{4} C H_{3}$ .
1 mark
(d)
Explain why pentane does not dissolve in water.
2 marks
(e)
State why liquid pentane does not conduct electricity.
1 mark

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