Chemical Combination: JAMB Chemistry Questions, Answers & Notes

What Chemical Combination covers in the JAMB Chemistry syllabus

The laws of chemical combination include conservation of mass (matter is neither created nor destroyed) and definite proportions (a compound always has a fixed mass ratio of its elements). The mole is the chemist's counting unit: one mole = 6.02 × 10²³ particles (Avogadro's number), has a mass equal to the molar mass in grams, and (for a gas) occupies about 22.4 dm³ at s.t.p. Moles = mass/molar mass = volume/22.4 (gas at s.t.p.). The empirical formula is the simplest whole-number atom ratio; the molecular formula is a whole-number multiple of it. Equations are balanced so each element has equal atoms on both sides.

For Chemical Combination, JAMB expects you to be able to:

• State the laws of chemical combination and conservation of mass
• Use the mole concept: molar mass, Avogadro's number and molar gas volume
• Determine empirical/molecular formulae and balance equations

Key facts & revision notes: Chemical Combination

These are the recurring points our Chemical Combination questions test — revise them until each feels automatic, then practise the questions above to lock them in.

• Mass is conserved: the total mass of products equals the total mass of reactants.
• A given compound always has its elements combined in a fixed proportion by mass.
• Relative atomic mass is measured on a scale where carbon-12 is exactly 12.
• One mole contains 6.02 × 10²³ particles (Avogadro's number).
• Moles = mass/molar mass = 36/18 = 2 mol.
• CO₂ = 12 + (2 × 16) = 12 + 32 = 44 g/mol.
• The empirical formula gives the simplest whole-number ratio of atoms present.
• The molecular formula is a whole-number multiple of the empirical formula.
• Molar mass of NaCl = 58.5 g/mol; 2 mol = 2 × 58.5 = 117 g.
• 0.5 × 6.02 × 10²³ = 3.01 × 10²³ atoms.
• Valency is an element's combining power, taken relative to hydrogen (valency 1).
• A balanced equation has equal numbers of each type of atom on both sides (mass conserved).
• 2H₂ + O₂ → 2H₂O balances 4 H and 2 O on each side.
• One mole of any gas occupies about 22.4 dm³ at standard temperature and pressure.
• Moles = volume/molar volume = 11.2/22.4 = 0.5 mol.
• Moles: C 40/12=3.33, H 6.7/1=6.7, O 53.3/16=3.33; ratio 1:2:1 → CH₂O.
• Avogadro's law: equal volumes of gases (same T and P) contain equal numbers of molecules.
• H₂SO₄ = (2×1) + 32 + (4×16) = 2 + 32 + 64 = 98.
• Molar mass CaCO₃ = 40 + 12 + 48 = 100 g/mol; 0.25 × 100 = 25 g.
• When two elements form more than one compound, the law of multiple proportions applies.
• One mole contains 6.02 × 10²³ particles.
• 40 + 12 + (3×16) = 100 g/mol.
• 2 × 6.02 × 10²³ = 1.204 × 10²⁴.
• N₂ + 3H₂ → 2NH₃ balances N and H.

Worked examples

Three Chemical Combination questions with the answer and a short explanation, so you can see how the topic is set before you practise the full set.

How Chemical Combination is tested in JAMB Chemistry

Our Chemical Combination bank holds 40 questions (4 easy, 26 medium, 10 hard). JAMB Chemistry typically returns to Chemical Combination year after year, so steady practice on this topic is high-value revision. Questions are multiple-choice with four options, and at UTME pace you get roughly 40 seconds each — which is why timed practice matters.

How to answer Chemical Combination questions

Work the stem first and predict the answer before you look at the options; then eliminate the ones that contradict the key facts above. Watch for “which is not…”, “all of the above” and “except” style stems, which are where rushed candidates lose easy marks on Chemical Combination. If a calculation or a precise definition is involved, work it from first principles rather than guessing from a half-remembered rule. When two options look right, re-read the stem for the qualifier that separates them — JAMB rarely repeats an option by accident. If you are still unsure, eliminate the two weakest choices to lift your odds, flag the question, and move on; never burn a full minute on one Chemistry item when the exam gives you about forty seconds each. Then come back to flagged questions with whatever time remains. The single most reliable way to get faster at Chemical Combination is repeated timed practice, so use the button above until the recurring patterns feel automatic.

Common mistakes to avoid in Chemical Combination

The errors that cost marks on Chemical Combination are usually careless rather than conceptual: misreading a negative stem, confusing two similar terms, or rushing a definition you actually know. Candidates also over-rely on “expo” and last-minute cramming instead of understanding the topic — which fails the moment JAMB rephrases a familiar idea. Treat every option as a claim to be checked against the facts above, keep your working tidy for any calculation, and don’t change a considered answer on a hunch. Above all, revise Chemical Combination actively by answering questions, not just by re-reading notes — recall under time is what the exam rewards.

Frequently asked questions

Is Chemical Combination part of the JAMB Chemistry syllabus?

Yes. Chemical Combination is a recognised topic in the JAMB Chemistry syllabus, covering state the laws of chemical combination and conservation of mass. You should be able to recall its key facts and apply them to multiple-choice questions.

How many Chemical Combination questions can I practise on Belmadeng?

There are 40 original, JAMB-standard Chemical Combination questions in our free bank, each with the correct answer and a worked explanation. You can practise them untimed or as a timed test.

What are the most important points to know about Chemical Combination?

The laws of chemical combination include conservation of mass (matter is neither created nor destroyed) and definite proportions (a compound always has a fixed mass ratio of its elements). The mole is the chemist's counting unit: one mole = 6.02 × 10²³ particles (Avogadro's number), has a mass equal…

How do I answer Chemical Combination questions quickly in JAMB?

Read the stem carefully, eliminate clearly wrong options, and match the remaining choices to the key facts for Chemical Combination. Practising timed Chemical Combination questions builds the speed you need for UTME's pace of about 40 seconds per question.

Are these JAMB Chemistry Chemical Combination questions past questions or original?

They are original questions written to JAMB (UTME) standard and mapped to the official syllabus — not reproduced past papers. This keeps them legal to use freely while closely mirroring how the real exam tests the topic.

Where can I practise Chemical Combination questions free without signing up?

Right here — tap “Start Chemical Combination practice” on this page to begin instantly. Belmadeng's CBT practice is completely free and needs no sign-up, download or subscription.

About these questions: original, JAMB-standard items written from the official UTME Chemistry syllabus (last reviewed 2026-09-18). Belmadeng is an independent study platform and is not affiliated with JAMB. Spotted an error? Use the report link.