Which molar volume should I use?

Use 24 dm3/mol at room conditions and 22.4 dm3/mol at STP; the question states which.

How do I find the limiting reagent?

Divide each reactant amount by its coefficient; the smallest value is limiting.

Mole and Stoichiometry, Paper 4: Error Review

2026-11-03

A review paper on molar mass, the 24 dm3 molar volume and limiting reagents. Convert to moles first, then to mass or volume.

Error review　Write the molar mass first, use moles as the middle unit, and double diatomic gases.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10
Suggested time	25
Difficulty mix	Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1
Chapter	Chapter: S4 Chemistry: The Mole and Stoichiometry
Level	S4

02　Questions (10 items)

FoundationWhat is the mass of 0.5 mol of oxygen gas, O2? (O = 16)
FoundationHow many moles are there in 3 g of hydrogen gas, H2? (H = 1)
FoundationHow many water molecules are there in 36 g of water? (H2O = 18, Avogadro constant 6.02e23)
FoundationHow many moles are there in 4.4 g of carbon dioxide, CO2? (C = 12, O = 16)
IntermediateWhat volume does 8.8 g of CO2 occupy at room conditions? (molar volume 24 dm3/mol)
IntermediateWhat is the mass of 6 dm3 of nitrogen gas, N2, at room conditions? (molar volume 24 dm3/mol, N = 14)
IntermediateWhat is the mass of 0.5 mol of sodium chloride, NaCl? (Na = 23, Cl = 35.5)
Challenge25 g of calcium carbonate, CaCO3, reacts completely with excess dilute hydrochloric acid. What volume of CO2 is released at room conditions? (CaCO3 = 100, molar volume 24 dm3/mol)
Challenge2 mol of hydrogen reacts completely with 1.5 mol of oxygen. What is the maximum mass of water formed, and how much of which reactant is left? (H2O = 18)
Error redoCorrect the statement: the mass of 3 mol of oxygen gas, O2, is 48 g. (O = 16)

03　Answers and one-line notes

#	Answer	One-line note
1	16 g	The molar mass is 32 g/mol, so 0.5 mol gives 16 g.
2	1.5 mol	The molar mass is 2 g/mol, and 3 / 2 = 1.5 mol.
3	1.204e24 molecules	36 g is 2 mol, and 2 x 6.02e23 = 1.204e24.
4	0.1 mol	The molar mass is 44 g/mol, and 4.4 / 44 = 0.1 mol.
5	4.8 dm3	This is 0.2 mol, and 0.2 x 24 = 4.8 dm3.
6	7 g	6 / 24 = 0.25 mol, and 0.25 x 28 = 7 g.
7	29.25 g	The molar mass is 58.5 g/mol, and 0.5 x 58.5 = 29.25 g.
8	6 dm3	25 g is 0.25 mol, the ratio to CO2 is 1:1, and 0.25 x 24 = 6 dm3.
9	36 g of water, with 0.5 mol of oxygen left	2 mol of H2 needs only 1 mol of O2, so oxygen is in excess; 2 mol of water is 36 g and 0.5 mol of O2 remains.
10	96 g	Oxygen is diatomic with a molar mass of 32 g/mol, so 3 x 32 = 96 g; 48 g forgets the factor of two.

04　What to do after marking

After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
Repeat the same item two days later; move to the next paper only when both attempts are correct.
Parents only need the answer and note columns; there is no need to explain every item.

Book an S4 Chemistry tutor Tutor Registration →

Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.