R2.1 How much? The amount of chemical change questions for IB Chemistry

220 questions on How much? The amount of chemical change, 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 R2 How much, how fast and how far?
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	63	2	65
Paper 1B	46	12	58
Paper 2	87	10	97
Every paper	196	24	220

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-00123Paper 1A · 1 mark

Aqueous silver nitrate is added to aqueous sodium chloride and a white precipitate forms. Which equation shows the correct state symbols?

A
$A g N O_{3} (a q) + N a C l (a q) \to A g C l (a q) + N a N O_{3} (s)$
B
$A g N O_{3} (a q) + N a C l (a q) \to A g C l (s) + N a N O_{3} (a q)$
C
$A g N O_{3} (s) + N a C l (s) \to A g C l (s) + N a N O_{3} (s)$
D
$A g N O_{3} (a q) + N a C l (a q) \to A g C l (l) + N a N O_{3} (a q)$

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Question 2 · 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

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Question 3 · CHEM-00416Paper 2 · 8 marks

Car airbags inflate when solid sodium azide, NaN₃, decomposes rapidly to produce nitrogen gas.

2 N a N_{3} (s) \to 2 N a (s) + 3 N_{2} (g)

An airbag has a volume of 60.0 dm³ when fully inflated. The gas in it is at 125 kPa and 27 °C.

(a)
Calculate the amount, in mol, of nitrogen in the inflated airbag. Use section 1 of the data booklet.
2 marks
(b)
Determine the mass, in g, of sodium azide needed.
2 marks
(c)
Immediately after it inflates, the gas in the bag is at 77 °C. Calculate the pressure of the gas at this temperature, assuming that the volume and amount of gas are the same as in (a).
2 marks
(d)
Explain why the nitrogen in the airbag can be treated as an ideal gas.
2 marks

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Question 4 · CHEM-00254Paper 1A · 1 mark

An organic compound contains carbon, hydrogen and oxygen only. Complete combustion of 0.450 g of the compound produces 0.660 g of $C O_{2}$ and 0.270 g of $H_{2} O$ .

$M (C O_{2}) = 44.01 {g mol}^{- 1}$ ; $M (H_{2} O) = 18.02 {g mol}^{- 1}$

What is the empirical formula of the compound?

A
$C H_{2}$
B
$C H O$
C
$C H_{4} O$
D
$C H_{2} O$

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Question 5 · CHEM-00514Paper 1B · 10 marks

The molar volume of hydrogen at room conditions was determined. Different masses of magnesium ribbon were each added to excess dilute hydrochloric acid in a conical flask connected to a gas syringe. Room temperature was 21.0 °C and pressure was 101.2 kPa.

Mass of Mg / g ± 0.001 g	0.020	0.030	0.040	0.050	0.060
Amount of Mg / mmol	0.823	1.234	1.645	2.057	2.468
Volume of H₂ / cm³ ± 0.5 cm³	19.5	28.5	34.0	47.0	57.5

line of best fit

Volume of hydrogen / cm³ (y) against amount of magnesium / mmol (x)

(a)
Write the equation for the reaction, including state symbols.
1 mark
(b)
Show that the amount of magnesium in 0.050 g is 2.057 mmol.
1 mark
(c)
Identify the anomalous result and suggest one reason for it.
2 marks
(d)
Determine the experimental molar volume of hydrogen, in dm³ mol⁻¹, from the gradient of the line of best fit.
2 marks
(e)
Calculate the theoretical molar volume of an ideal gas, in dm³ mol⁻¹, at the conditions of the experiment. Use section 1 of the data booklet.
1 mark
(f)
Calculate the percentage error in the experimental value.
1 mark
(g)
The experimental value is consistently lower than the theoretical value. Suggest one systematic error that would cause this, and a modification to reduce it.
2 marks

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Question 6 · CHEM-00421Paper 2 · 7 marks

Calcium carbonate decomposes on strong heating to form calcium oxide and carbon dioxide.

A student heated 2.50 g of calcium carbonate until there was no further change in mass.

(a)
Write the equation for the reaction, including state symbols.
1 mark
(b)
Calculate the amount, in mol, of carbon dioxide produced.
1 mark
(c)
Calculate the volume, in cm³, of this carbon dioxide at 25 °C and 100 kPa.
2 marks
(d)
The carbon dioxide was collected over water in an inverted measuring cylinder. Suggest one reason why the volume collected was less than the value in (c).
1 mark
(e)
Explain why carbon dioxide deviates more from ideal behaviour than nitrogen under the same conditions.
2 marks

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