JAMB Chemistry 2018 past questions

Checked by the Skolra question team · Last updated 15 October 2026

Ten questions from the 2018 JAMB Chemistry paper, with answers and explanations. We hold 87 questions from this paper, and the Skolra app has all of them.

JAMB Chemistry 2018 questions and answers

1.
When air which contains the gases Oxygen, nitrogen, carbondioxide, water vapour and the rare gases, is passed through alkaline pyrogallol and then over quicklime, the only gases left are;
1. A
  nitrogen and the rare (noble) gases
  Correct
2. B
  carbon(IV) oxide and water vapour
3. C
  oxygen and nitrogen
4. D
  oxygen and the rare gases
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Answer: A
Alkaline pyrogallol absorbs oxygen from the air, and quicklime (calcium oxide) absorbs both carbon(IV) oxide and water vapour. What is left after both steps are the unreactive gases that neither treatment removes: nitrogen and the rare (noble) gases.
Oxygen cannot remain, since it is the very gas alkaline pyrogallol is used to absorb. Carbon(IV) oxide and water vapour are both removed by the quicklime step, so they cannot be what is "left". Oxygen is absorbed before the noble gases could ever be isolated alongside it.
2.
The refreshing and characteristic taste of soda water and other soft drinks is as a result of the presence of
1. A
  dissolved nitrogen gas
2. B
  dissolved oxygen gas
3. C
  dissolved sulphur(IV) oxide
4. D
  dissolved carbon(IV) oxide
  Correct
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Answer: D
Soft drinks are carbonated under pressure with dissolved carbon(IV) oxide. When the bottle is opened, the gas escapes as fizzing bubbles and also forms a little carbonic acid in the drink, giving it its sharp, refreshing taste.
Nitrogen and oxygen are far less soluble in water under normal bottling pressure and are not deliberately added for this purpose. Sulphur(IV) oxide has a harsh, choking smell and is used as a preservative in some products, not as the source of a pleasant fizzy taste.
3.
The alkanoic acid found in human sweat is
1. A
  ethanoic acid
2. B
  butanoic acid
  Correct
3. C
  methanoic acid
4. D
  propanoic acid
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Answer: B
Butanoic acid (butyric acid) is the short-chain fatty acid responsible for the characteristic sour odour of human sweat and of rancid butter.
Methanoic acid is the acid in ant and nettle stings, not sweat. Ethanoic acid is the acid of vinegar. Propanoic acid is used mainly as a food preservative. None of these three is the acid associated with sweat's smell.
4.
How many atoms are present in 6.0g of magnesium? [Mg = 24, N.A = 6.02 x 10 $^{23}$ mol]
1. A
  1.505 × 10²³
  Correct
2. B
  6.02 × 10²³
3. C
  2.408 × 10²⁴
4. D
  3.01 × 10²³
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Answer: A
Moles of Mg = 6.0 ÷ 24 = 0.25 mol. Number of atoms = 0.25 × 6.02×10²³ = 1.505×10²³ atoms.
3.01×10²³ would be the count for 0.5 mol (12g) of magnesium, twice the mass actually given. 6.02×10²³ is Avogadro's number itself, the count for a full mole (24g), not for 6g. 2.408×10²⁴ would only be correct for 96g of magnesium.
5.
A quantity of electricity liberates 3.6g of Silver from its salt. What mass of aluminium Will be liberated from its salt by the same quantity of electricity? [Al = 27, Ag = 108].
1. A
  0.10g
2. B
  2.70g
3. C
  0.30g
  Correct
4. D
  0.90g
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Answer: C
Moles of Ag deposited = 3.6 ÷ 108 = 0.0333 mol, requiring 0.0333 mol of electrons (Ag⁺ + e⁻ → Ag). The same charge deposits aluminium via Al³⁺ + 3e⁻ → Al, needing 3 electrons per atom, so moles of Al = 0.0333 ÷ 3 = 0.0111 mol. Mass = 0.0111 × 27 = 0.30g.
0.10g would come from dividing by 9 instead of 3 electrons. 0.90g comes from forgetting to divide by 3 electrons at all. 2.70g does not correspond to a consistent use of Faraday's laws with the given data.
6.
An element used in the production of matches is
1. A
  carbon
2. B
  sulphur
3. C
  phosphorus
  Correct
4. D
  silicon
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Answer: C
Phosphorus (typically red phosphorus) is used on the striking surface of matchboxes and in match heads, since it ignites readily from the friction and heat of striking.
Sulphur is present in some match-head formulations as a fuel but is not the defining element the question is testing; carbon and silicon play no characteristic role in match manufacture at all.
7.
Which of the following is an example of a chemical change?
1. A
  Rusting of iron
  Correct
2. B
  Melting of ice
3. C
  Dissolving sugar in water
4. D
  Boiling of water
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Answer: A
Rusting of iron forms a genuinely new substance, hydrated iron(III) oxide, through a reaction with oxygen and moisture, and this change cannot be reversed simply by physical means — the hallmark of a chemical change.
Melting ice, dissolving sugar and boiling water are all physical changes: no new substance is formed, and each can be reversed (freezing, evaporating and recrystallising, or condensing) without any chemical reaction taking place.
8.
Diamond is a bad conductor of electricity because its bonding electrons are used in
1. A
  delocalised metallic bonding across the whole crystal
2. B
  strong, localised covalent bonds between each carbon atom
  Correct
3. C
  ionic bonds between positive and negative ions
4. D
  weak van der Waals forces between separate layers
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Answer: B
In diamond, every carbon atom uses all four valence electrons to form four strong, localised covalent bonds to its neighbours. With no free or delocalised electrons left over, there is nothing available to carry an electric current, so diamond does not conduct.
Metallic bonding (with a "sea" of delocalised electrons) is what allows metals to conduct, but diamond's bonding is covalent, not metallic. Diamond has no separate layers held by weak van der Waals forces (that describes graphite instead). Diamond is not ionic either — it has no charged ions, only covalently bonded carbon atoms.
9.
The periodic classification is an arrangement of the elements
1. A
  alphabetically by their chemical symbols
2. B
  in order of increasing atomic mass only
3. C
  randomly, based only on date of discovery
4. D
  in order of increasing atomic number
  Correct
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Answer: D
The modern periodic table arranges elements strictly in order of increasing atomic number — the number of protons in the nucleus — which is the basis of the modern periodic law.
Ordering by atomic mass was the older, Mendeleev-era approach and produces a few well-known inconsistencies (such as tellurium and iodine) compared to ordering by atomic number. The table is not arranged alphabetically by symbol, and it is certainly not random or based on when each element happened to be discovered.
10.
The conductivity of an acid solution depends on the
1. A
  concentration of hydrogen ions present
  Correct
2. B
  colour of the acid
3. C
  boiling point of the acid
4. D
  molecular mass of the acid
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Answer: A
Electrical conductivity in an acid solution comes from the movement of free ions. The more an acid ionises, the more hydrogen ions (and the corresponding anions) are present to carry charge, so conductivity tracks the concentration of these ions, not just the concentration of the acid itself.
Colour has nothing to do with charge carriers. Boiling point is a physical property unrelated to ion concentration. Molecular mass affects the weight of the acid, not how many ions it releases into solution.

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JAMB Chemistry 2018 past questions

JAMB Chemistry 2018 questions and answers

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