S1.4 Counting particles by mass: the mole questions for IB Chemistry

175 questions on Counting particles by mass: the mole, 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 S1 Models of the particulate nature 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	73	2	75
Paper 1B	28	4	32
Paper 2	62	6	68
Every paper	163	12	175

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-00016Paper 1A · 1 mark

Two identical sealed flasks are at the same temperature and pressure. One contains helium and the other contains methane. Which is the same for both flasks? Assume ideal behaviour.

A
The number of gas particles
B
The number of atoms
C
The mass of gas
D
The density of the gas

The answer and whyCheck this one with a free account

Question 2 · CHEM-00510Paper 1B · 10 marks

A student determined the number of molecules of water of crystallization, x, in hydrated copper(II) sulfate, CuSO₄·xH₂O.

Method:

A clean, dry crucible was weighed.
Blue hydrated copper(II) sulfate was added and the crucible was reweighed.
The crucible was heated gently, allowed to cool, and reweighed.
Step 3 was repeated until two consecutive masses agreed.

Measurement	Mass / g ± 0.001 g
Empty crucible	18.452
Crucible + hydrated salt	20.947
Crucible + solid after first heating	20.183
Crucible + solid after second heating	20.051
Crucible + solid after third heating	20.049

The solid at the end was white.

(a)
Explain why the crucible was heated until two consecutive masses agreed.
1 mark
(b)
Calculate the mass of water lost.
1 mark
(c)
Determine the value of x.
3 marks
(d)
Calculate the percentage uncertainty in the mass of water lost.
2 marks
(e)
In a second experiment, the student heated the crucible strongly and some of the solid turned black, as copper(II) sulfate decomposed to copper(II) oxide. Predict, with a reason, the effect on the calculated value of x.
2 marks
(f)
The crucible was left to cool on the open bench before each weighing. Suggest a modification to the method, explaining how it improves the result.
1 mark

The markschemeCheck this one with a free account

Question 3 · CHEM-00415Paper 2 · 9 marks

A gaseous hydrocarbon, X, contains 85.6 % carbon and 14.4 % hydrogen by mass. A 0.255 g sample of X occupies 150.0 cm³ at 25.0 °C and 100.0 kPa.

(a)
Determine the empirical formula of X.
2 marks
(b)(i)
Calculate the molar mass of X, in g mol⁻¹. Use sections 1 and 2 of the data booklet.
3 marks
(b)(ii)
Deduce the molecular formula of X.
1 mark
(c)
State one assumption made in using the ideal gas equation in (b)(i).
1 mark
(d)
The experiment is repeated at a temperature just above the boiling point of X. Explain why the value of the molar mass obtained would be less accurate.
2 marks

The markschemeCheck this one with a free account

Question 4 · CHEM-00047Paper 1A · 1 mark

A compound has the empirical formula $C_{2} H_{4} O$ and a relative molecular mass of 88.

Which could be the compound?

I. Butanoic acid
II. Ethyl ethanoate
III. Butan-1-ol

A
I and II only
B
I and III only
C
II and III only
D
I, II and III

The answer and whyCheck this one with a free account

Question 5 · CHEM-00511Paper 1B · 9 marks

The empirical formula of magnesium oxide was determined by heating magnesium ribbon in a crucible. The lid of the crucible was lifted slightly from time to time during heating. The crucible was heated to constant mass.

Measurement	Mass / g ± 0.001 g
Crucible + lid	25.314
Crucible + lid + magnesium	25.554
Crucible + lid + product (constant mass)	25.701

(a)
Calculate the mass of oxygen that combined with the magnesium.
1 mark
(b)
Determine the empirical formula of magnesium oxide from these results.
2 marks
(c)
Explain why the lid was used, and why it was lifted from time to time.
2 marks
(d)
Calculate the percentage error in the mass of product compared with the mass expected if all the magnesium formed MgO.
1 mark
(e)
Some of the magnesium reacts with nitrogen in the air to form magnesium nitride, Mg₃N₂. Write the equation for this reaction and predict its effect on the experimental Mg : O ratio.
2 marks
(f)
Suggest one modification that would convert any magnesium nitride into magnesium oxide.
1 mark

The markschemeCheck this one with a free account

Question 6 · CHEM-00420Paper 2 · 7 marks

Weather balloons are filled with helium and released to measure conditions in the upper atmosphere. A balloon is filled with 5.00 m³ of helium at 101 kPa and 15 °C.

(a)
Calculate the mass, in g, of helium in the balloon.
2 marks
(b)
At an altitude of 25 km the pressure is 2.50 kPa and the temperature is −51 °C. Calculate the volume, in m³, of the balloon at this altitude, assuming no helium escapes.
2 marks
(c)
Outline why the balloon expands as it rises, even though the temperature falls.
1 mark
(d)
Suggest why helium behaves almost as an ideal gas under these conditions.
2 marks

The markschemeCheck this one with a free account

Practice all 175 in Augment

Free with an account. Every question has its markscheme, and Augment keeps the ones you got wrong so you can come back to them.

Start free Log in

The notes on S1.4 Counting particles by mass: the mole

Check your answers in Augment

A free account opens all 175 questions on Counting particles by mass: the mole with their markschemes, and keeps a record of what you have marked.

Start free

Questions by paper and level

Questions to try

Practice all 175 in Augment

More questions in Models of the particulate nature of matter

Check your answers in Augment