JAMB Chemistry 2012 Objective Past Questions

All 50 questions from the Joint Admissions and Matriculation Board (JAMB) Chemistry 2012 Objective paper, with the correct answer and a full explanation for each. Free, no signup needed.

Chemistry 2012 Objective — Question 1

Which Question Paper Type of Chemistry as indicated above is given to you?

• A. Type Green
• B. Type Purple
• C. Type Red
• D. Type YellowCorrect

Explanation

This is a type Yellow Chemistry Question Paper.

Chemistry 2012 Objective — Question 2

Which of the following methods can be used to obtain pure water from a mixture of sand, water and methanoic acid?

• A. Neutralization with NaOH followed by filtration
• B. Neutralization with NaOH followed by distillation
• C. Fractional distillation
• D. Filtration followed by distillationCorrect

Explanation

The sand can be removed using filtration. The water can be separated from the methanoic acid by distillation. Since methanoic acid is of a lower boiling point than water, it distils over first.

Chemistry 2012 Objective — Question 3

How many atoms are present in 6.0g of magnesium? [Mg=24, Na=6.02×10²³ mol⁻¹]

• A. 1.20×10²²
• B. 2.41×10²³
• C. 1.51×10²³Correct
• D. 3.02×10²³

Explanation

Mass of magnesium = 6.0g. Molar mass of magnesium = 24g/mol. Mole = Mass/Molar mass = 6/24 = 0.25mol. Number of Mg atoms = Mole of Mg × Avogadro's number = 0.25×6.02×10²³ = 1.505×10²³.

Chemistry 2012 Objective — Question 4

50 cm³ of a gas was collected over water at 10°C and 765 mm Hg. Calculate the volume of the gas at s.t.p. if the saturated vapour pressure of water at 10°C is 5mm Hg.

• A. 49.19cm³Correct
• B. 48.87cm³
• C. 48.55cm³
• D. 48.23cm³

Explanation

P1=765−5=760mmHg, V1=50cm³, T1=283K (10°C+273); P2=760mmHg, T2=273K, V2=?. Using the general gas law: P1V1/T1=P2V2/T2, giving V2 ≈ 49.19cm³ (per printed key, option A).

Chemistry 2012 Objective — Question 5

An increase in the pressure exerted on a gas at a constant temperature results in a

• A. decrease in the number of effective collisions
• B. decrease in volumeCorrect
• C. an increase in the average intermolecular distance
• D. an increase in volume

Explanation

An increase in the pressure exerted on a gas at a constant temperature results in a decrease in volume, consistent with Boyle's law.

Chemistry 2012 Objective — Question 6

2H2(g) + O2(g) → 2H2O(g). In the reaction above, what volume of hydrogen would be left over when 300cm³ of oxygen and 1000cm³ of hydrogen are exploded in a sealed tube?

• A. 200cm³
• B. 400cm³Correct
• C. 600cm³
• D. 700cm³

Explanation

From the equation, mole ratio of H2:O2 = 2:1. 300cm³ of oxygen will react with 600cm³ of hydrogen. Excess hydrogen = (1000−600)cm³ = 400cm³.

Chemistry 2012 Objective — Question 7

I. Evaporation II. Sublimation III. Diffusion IV. Brownian motion. Which of the above can correctly be listed as evidences for the particulate nature of matter?

• A. I and III only
• B. II and IV only
• C. I,II and III only
• D. I, II, III and IVCorrect

Explanation

Evaporation, sublimation, diffusion, and Brownian motion are all evidences that particles making up matter are in constant motion — supporting the particulate nature of matter.

Chemistry 2012 Objective — Question 8

If the elements X and Y have atomic numbers 11 and 17 respectively, what type of bond can they form?

• A. Dative
• B. Covalent
• C. IonicCorrect
• D. Metallic

Explanation

X (atomic number 11) is sodium, with electron configuration 2,8,1 — it readily loses one electron. Y (atomic number 17) is chlorine, with configuration 2,8,7 — it readily gains one electron. This electron transfer forms an ionic bond.

Chemistry 2012 Objective — Question 9

A hydrogen atom which has lost an electron contains

• A. one proton onlyCorrect
• B. one neutron only
• C. one proton and one neutron
• D. one proton, one electron and one neutron

Explanation

A hydrogen atom has one proton and one electron (no neutron in the common isotope). If it loses its electron, it is left with one proton only.

Chemistry 2012 Objective — Question 10

The electronic configuration of Mg²⁺ is

• A. 1s²2s²2p⁶3s²3p2
• B. 1s²2s²2p⁶3s²
• C. 1s²2s²2p⁶Correct
• D. 1s²2s²2p⁴

Explanation

Magnesium (Mg) has electron configuration 1s²2s²2p⁶3s². Losing two electrons to form Mg²⁺ gives 1s²2s²2p⁶.

Chemistry 2012 Objective — Question 11

Group VII elements are

• A. monoatomic
• B. good oxidizing agentsCorrect
• C. electropositive
• D. metallic

Explanation

Group VII elements (halogens) are good oxidizing agents, being highly electronegative and readily accepting electrons.

Chemistry 2012 Objective — Question 12

Two elements, X and Y are in the same group on the periodic table because they both have the same

• A. number of electronic shells
• B. number of valence electronsCorrect
• C. atomic size
• D. atomic number

Explanation

Elements in the same group have the same number of valence (outermost) electrons.

Chemistry 2012 Objective — Question 13

Air has a varied composition from one place to another; its constituents can be separated by physical means; it contains unreactive noble gases. Which of the above shows that air is a mixture?

• A. I and II only
• B. II and III only
• C. I and III only
• D. I, II and IIICorrect

Explanation

Air's varied composition, physical separability, and its unreactive noble gas content are all evidence supporting that air is a mixture.

Chemistry 2012 Objective — Question 14

The chemicals used to soften hard water involves the addition of

• A. insoluble sodium compounds which form soluble solutions of calcium and magnesium ions
• B. soluble sodium compounds which form soluble solutions of calcium and magnesium ions
• C. soluble sodium compounds which form insoluble precipitates of calcium and magnesium ionsCorrect
• D. insoluble sodium compounds which form insoluble precipitates of calcium and magnesium ions

Explanation

Softening hard water involves the addition of soluble sodium compounds which form insoluble precipitates of calcium and magnesium ions, thereby removing them from solution.

Chemistry 2012 Objective — Question 15

Chlorination of water for town supply is carried out to

• A. make the water colourless
• B. remove germs from the waterCorrect
• C. make the water tasteful
• D. remove odour from the water

Explanation

Chlorination of water for town supply is carried out to remove germs from the water.

Chemistry 2012 Objective — Question 16

Which of the following pollutants is associated with brain damage?

• A. Carbon (II) oxideCorrect
• B. Radioactive fallout
• C. Biodegradable waste
• D. Sulphur (IV) oxide

Explanation

Carbon (II) oxide (carbon monoxide) is associated with brain damage, as it binds to haemoglobin and starves the brain of oxygen.

Chemistry 2012 Objective — Question 17

Which of the following will produce a solution with pH less than 7 at equivalent point?

• A. HNO3+ NaOH
• B. H2SO4+ KOH
• C. HCl+ Mg(OH)2Correct
• D. HNO3+ KOH

Explanation

HCl+Mg(OH)2 is a reaction between a strong acid and a weak base; at the equivalence point the resulting salt solution hydrolyses to give a pH less than 7 (acidic).

Chemistry 2012 Objective — Question 18

Which of the following is a polysaccharide?

• A. Glucose
• B. Sucrose
• C. Maltose
• D. CelluloseCorrect

Explanation

Glucose is a monosaccharide, sucrose and maltose are disaccharides. Starch, cellulose, etc. are polysaccharides.

Chemistry 2012 Objective — Question 19

Write the structure of the amino acid, CH3CH(NH2)COOH in acidic medium and alkaline medium.

• A. CH3CH(NH3+)COOH in acid; CH3CH(NH2)COO− in alkaliCorrect
• B. CH3CH(NH2)COOH in acid; CH3CH(NH3+)COO− in alkali
• C. CH3CH(NH3+)COO− in both
• D. CH3CH(NH2)COOH in both

Explanation

In acidic medium, the amino acid exists predominantly as CH3CH(NH3⁺)COOH. In alkaline medium, it exists predominantly as CH3CH(NH2)COO⁻.

Chemistry 2012 Objective — Question 20

The number of hydroxonium ions produced by one molecule of an acid in aqueous solution is its

• A. basicityCorrect
• B. acid strength
• C. pH
• D. concentration

Explanation

The basicity of an acid is defined as the number of hydroxonium (H3O⁺) ions that can be produced by one molecule of the acid in aqueous solution. HCl, H2SO4 and H3PO4 have basicity of 1, 2, and 3 respectively.

Chemistry 2012 Objective — Question 21

During a titration experiment, 0.05 moles of carbon(IV) oxide is liberated. What is the volume of gas liberated? [Molar volume of a gas at s.t.p.=22.4dm³]

• A. 22.40dm³
• B. 11.20dm³
• C. 2.24dm³
• D. 1.12dm³Correct

Explanation

Volume = Mole × GMV = 0.05×22.4 = 1.12dm³.

Chemistry 2012 Objective — Question 22

A major factor considered in selecting a suitable method for preparing a simple salt is its

• A. crystalline form
• B. melting point
• C. reactivity with dilute acids
• D. solubility in waterCorrect

Explanation

Solubility in water is a major factor to be considered when selecting a suitable method for preparing a salt. For instance, a water-insoluble salt like AgCl can be obtained by double decomposition: AgNO3(aq)+NaCl(aq)→AgCl(s)+NaNO3(aq).

Chemistry 2012 Objective — Question 23

The oxidation number of boron in NaBH4 is

• A. -3
• B. -1
• C. +1
• D. +3Correct

Explanation

NaBH4 is sodium tetrahydridoborate (III). Na=+1, H=−1 (each of 4 hydrogens). +1+B+(−1×4)=0 ⇒ 1+B−4=0 ⇒ B=+3.

Chemistry 2012 Objective — Question 24

2Na2O2(s) + 2H2O(l) →4NaOH(s) + O2(g). The substance that is oxidized in the reaction above is

• A. 2Na2O2(s)Correct
• B. NaOH(aq)
• C. H2O(l)
• D. O2(g)

Explanation

In this reaction, the oxidation number of oxygen in Na2O2 (peroxide, −1) increases to 0 in O2, meaning Na2O2 is oxidized.

Chemistry 2012 Objective — Question 25

What number of moles of Cu²⁺ will be deposited by 360 coulombs of electricity? [F=96,500C]

• A. 5.36×10⁻⁴ mole
• B. 1.87×10⁻³ moleCorrect
• C. 9.35×10⁻³ mole
• D. 3.73×10⁻³ mole

Explanation

1 mole of Cu²⁺ requires 2F (96,500C×2). Thus, 360C will only produce (1/(2×96,500))×360 mole = 1.87×10⁻³ mole.

Chemistry 2012 Objective — Question 26

A metal M displaces zinc from ZnCl2 solution. This shows that M is

• A. less electronegative than zinc
• B. more electropositive than zincCorrect
• C. more electronegative than zinc
• D. less electropositive than zinc

Explanation

For a metal to displace another metal from its solution, the former must be more electropositive than the latter.

Chemistry 2012 Objective — Question 27

CO(g) +H2O(g)→ CO2(g)+H2(g). Calculate the standard heat change of the reaction above, if the standard enthalpies of formation of CO2(g), H2O and CO(g) in kJ mol⁻¹ are -394, -242 and -110 respectively.

• A. +262kJ mol⁻¹
• B. -262kJ mol⁻¹
• C. +42kJ mol⁻¹
• D. -42kJ mol⁻¹Correct

Explanation

ΔH = ΣH(products) − ΣH(reactants) = −394 − (−352) = −42kJ mol⁻¹, where ΣH(reactants) = −110+(−242) = −352.

Chemistry 2012 Objective — Question 28

An increase in entropy can best be illustrated by

• A. mixing of gasesCorrect
• B. freezing of water
• C. condensation of vapour
• D. solidifying candle wax

Explanation

Entropy is the degree of disorderliness or randomness of a system. When gases are mixed, there is great disorder, so entropy increases substantially.

Chemistry 2012 Objective — Question 29

The highest rate of production of carbon (IV) oxide can be achieved using

• A. 0.05 mol dm⁻³ HCl and 5g powdered CaCO3
• B. 0.05 mol dm⁻³ HCl and 5g lump CaCO3
• C. 0.10 mol dm⁻³ HCl and 5g powdered CaCO3Correct
• D. 0.025mol dm⁻³ HCl and 5g powdered CaCO3

Explanation

Higher concentration and powdered form (greater surface area) both increase reaction rate; the option with both 0.10 mol dm⁻³ HCl and powdered CaCO3 gives the fastest reaction.

Chemistry 2012 Objective — Question 30

2HCl(aq) + CaCO3(s) → CaCl2 + CO2(g) + H2O(l). From the reaction above, which of the curves represents the production of CO2 gas as dilute HCl is added to the apparatus shown (with an empty flask, sodium, and water)?

• A. L
• B. MCorrect
• C. N
• D. P

Explanation

Curve M represents the production of CO2 gas over time as dilute HCl is gradually added to the calcium carbonate, based on the shape of gas evolution shown in the source diagram.

Chemistry 2012 Objective — Question 31

2CO(g)+ O2(g)⇌2CO2(g). In the reaction above, high pressure will favour the forward reaction because

• A. high pressure favours gas formation
• B. the reaction is in dynamic equilibrium
• C. the reaction is exothermic
• D. the process occurs with a decrease in volumeCorrect

Explanation

High pressure will favour the forward reaction because the process occurs with a decrease in volume (fewer moles of gas on the product side).

Chemistry 2012 Objective — Question 32

A piece of filter paper moistened with lead(II) ethanoate solution turns black when the paper is dropped into a gas jar containing an unknown gas. The gas is likely to be

• A. sulphur(IV) oxide
• B. hydrogen chloride
• C. sulphur(VI) oxide
• D. hydrogen sulphideCorrect

Explanation

Lead(II) ethanoate paper turning black indicates the presence of hydrogen sulphide gas, which reacts to form black lead(II) sulphide.

Chemistry 2012 Objective — Question 33

A spot of oil paint on a shirt can best be removed using

• A. turpentine
• B. detergent
• C. keroseneCorrect
• D. warm water

Explanation

A spot of oil paint on a shirt can be removed effectively using kerosene, a good solvent for oil.

Chemistry 2012 Objective — Question 34

Commercial bleaching can be carried out using

• A. sulphur(IV) oxide and ammonia
• B. hydrogen sulphide and chlorine
• C. chlorine and sulphur(IV) oxideCorrect
• D. ammonia and chlorine

Explanation

Commercial bleaching can be carried out using chlorine and sulphur(IV) oxide.

Chemistry 2012 Objective — Question 35

Mineral acids are usually added to commercial hydrogen peroxide to

• A. oxidize it
• B. decompose it
• C. minimize its decompositionCorrect
• D. reduce it to water and oxygen

Explanation

Mineral acids are added to commercial hydrogen peroxide to minimize its decomposition, stabilizing the solution.

Chemistry 2012 Objective — Question 36

Which of the following compounds will burn with a brick-red colour in a non-luminous Bunsen flame?

• A. LiCl
• B. NaCl
• C. CaCl2Correct
• D. MgCl2

Explanation

Calcium chloride (CaCl2) burns with a brick-red flame colour, characteristic of calcium ions.

Chemistry 2012 Objective — Question 37

The purest form of iron which contains only about 0.1% carbon is

• A. pig iron
• B. wrought ironCorrect
• C. cast iron
• D. iron pyrite

Explanation

Wrought iron is the purest form of iron, containing only about 0.1% carbon.

Chemistry 2012 Objective — Question 38

A common characteristic between zinc and the other transition elements is the

• A. ability to have variable oxidation states
• B. ability to form complex ionsCorrect
• C. ability to act as a catalyst
• D. ability to form coloured ions

Explanation

Like other transition elements, zinc also forms complex ions. Zinc has a fixed +2 oxidation state (i.e. it does not have variable oxidation states) and, having a completely filled d-orbital, does not give coloured ions.

Chemistry 2012 Objective — Question 39

Which of the following metals is the least reactive?

• A. Pb
• B. Sn
• C. Hg
• D. AuCorrect

Explanation

Gold is the least reactive of the metals, according to the electrochemical series (K, Na, Ca, Mg, Al, Zn, Fe, Sn, Pb, H, Cu, Hg, Ag, Au — decreasing reactivity).

Chemistry 2012 Objective — Question 40

Geometric isomerism can exist in

• A. hex-3-eneCorrect
• B. hexane
• C. prop-1-ene
• D. 3-methyl but-1-ene

Explanation

Geometric (cis-trans) isomerism requires restricted rotation around a double bond with two different groups on each carbon of the double bond. Hex-3-ene satisfies this condition; the others do not.

Chemistry 2012 Objective — Question 41

Alkanals can be distinguished from alkanones by the reaction with

• A. sudan III stain
• B. starch iodide paper
• C. lithium tetrahydrido aluminate(III)
• D. Fehling's solutionCorrect

Explanation

Alkanals (aldehydes) give a positive test with Fehling's solution (forming a brick-red precipitate), while alkanones (ketones) do not.

Chemistry 2012 Objective — Question 42

The isomers of C3H8O are

• A. 1-propanol and 2-propanolCorrect
• B. 1-propanal and 2-propanal
• C. 2-propanol and 2-propanone
• D. 2-propanol and 1-propanal

Explanation

The isomers of C3H8O are 1-propanol and 2-propanol.

Chemistry 2012 Objective — Question 43

Carbohydrates are large molecules with the molecular formula Cx(H2O)y. In which of the following pairs is x not equal to y?

• A. Glucose and starch
• B. Maltose and fructose
• C. Sucrose and fructoseCorrect
• D. Maltose and starch

Explanation

Glucose C6H12O6=C6(H2O)6 (x=y=6). Fructose is also C6H12O6 (x=y=6). Sucrose C12H22O11=C12(H2O)11 (x=12,y=11, x≠y). Thus for the sucrose/fructose pair, x is not equal to y for sucrose (unlike fructose, where x=y).

Chemistry 2012 Objective — Question 44

A compound contains 40.0% C, 6.7% H and 53.3% O. If the molecular mass of the compound is 180, its molecular formula is [C=12, H=1, O=16]

• A. CH2O
• B. C3H6O3
• C. C6H6O3
• D. C6H12O6Correct

Explanation

Empirical formula from percentages (40.0/12 : 6.7/1 : 53.3/16 ≈ 1:2:1) gives CH2O (empirical mass 30). Since molecular mass is 180, n=180/30=6, so molecular formula = C6H12O6.

Chemistry 2012 Objective — Question 45

The alkyne that will give a white precipitate with silver trioxonitrate(V) is

• A. CH3CH2C≡CCH2CH3
• B. CH3C≡CCH2CH3
• C. CH3CH2CH2C≡CHCorrect
• D. CH3CH2CH2C≡CCH3

Explanation

A terminal alkyne is one that has the triple bond at the end of the chain, e.g. CH3CH2CH2C≡CH. Only terminal alkynes give a white precipitate with silver trioxonitrate(V).

Chemistry 2012 Objective — Question 46

The saponification of an alkanoate to produce soap and alkanol involves

• A. dehydration
• B. esterification
• C. hydrolysisCorrect
• D. oxidation

Explanation

Saponification is a typical hydrolytic reaction involving oil (alkanoate) and alkali to form soap and alkanol (glycerol).

Chemistry 2012 Objective — Question 47

2-methylpropan-2-ol is an example of a

• A. primary alkanol
• B. secondary alkanol
• C. tertiary alkanolCorrect
• D. quarternary alkanol

Explanation

2-methylpropan-2-ol is a tertiary alkanol. A tertiary alkanol has three alkyl groups attached to the carbon atom that carries the OH functional group.

Chemistry 2012 Objective — Question 48

The final oxidation product of alkanol, alkanal and alkanones is

• A. alkanoic acidCorrect
• B. alkanoyl halide
• C. alkanamide
• D. alkanoate

Explanation

The final oxidation product of alkanol, alkanal and alkanones is alkanoic acid.

Chemistry 2012 Objective — Question 49

Ethanol reacts with concentrated tetraoxosulphate(VI) at a temperature above 170°C to form

• A. ethanamine
• B. ethanone
• C. ethanoic acid
• D. etheneCorrect

Explanation

Ethanol reacts with concentrated H2SO4 at about 180°C to produce ethene upon total dehydration.

Chemistry 2012 Objective — Question 50

An example of oxidation-reduction enzyme is

• A. amylase
• B. protease
• C. lipase
• D. dehydrogenaseCorrect

Explanation

Dehydrogenase is the degree of an oxidation-reduction enzyme.