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JAMB Chemistry 2014 past questions and answers

46 questions. Try each one, then open the answer to check yourself and read the explanation.

Question 2

Separation of Mixtures

A mixture is different from a compound because

  1. A.the properties of a compound are those of its individual constituents while those of a mixture differ from its constituents
  2. B.a mixture is always homogeneous while a compound is not
  3. C.the constituents of a compound are chemically bound together while those of a mixture are not
  4. D.a mixture can be represented by a chemical formula while a compound cannot
Show the answer and explanation

Answer: C (the constituents of a compound are chemically bound together while those of a mixture are not)

Explanation

In a compound the elements are chemically combined; in a mixture the parts are only mixed physically and can be separated by physical means.

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Question 3

Mole Concept and Stoichiometry

What is the percentage of sulphur in sulphur(IV) oxide? [S = 32, O = 16]

  1. A.66%
  2. B.25%
  3. C.40%
  4. D.50%
Show the answer and explanation

Answer: D (50%)

Explanation

SO2 has molar mass 32 + 32 = 64 g. % S = 32/64 × 100 = 50%.

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Question 4

Gas Laws

A gas X diffuses twice as fast as gas Y. If the relative molecular mass of X is 32, calculate the relative molecular mass of Y.

  1. A.128
  2. B.8
  3. C.16
  4. D.64
Show the answer and explanation

Answer: A (128)

Explanation

Graham's law: rate X/rate Y = √(MY/MX). So 2 = √(MY/32), giving MY = 4 × 32 = 128.

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Question 5

Gas Laws

200 cm3 of a gas at 25 °C exerts a pressure of 700 mmHg. Calculate its pressure if its volume increases to 350 cm3 at 75 °C.

  1. A.342.53 mmHg
  2. B.1430.54 mmHg
  3. C.467.11 mmHg
  4. D.400.00 mmHg
Show the answer and explanation

Answer: C (467.11 mmHg)

Explanation

P1V1/T1 = P2V2/T2: P2 = (700 × 200 × 348)/(298 × 350) = 467.11 mmHg (temperatures in kelvin).

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Question 6

Periodic Table

An element X has electron configuration 1s2 2s2 2p6 3s2 3p5. Which of the following statements is correct about the element?

  1. A.It has a completely filled p-orbital.
  2. B.It has 5 electrons in its outermost shell.
  3. C.It belongs to group II on the periodic table.
  4. D.It is a halogen.
Show the answer and explanation

Answer: D (It is a halogen.)

Explanation

X has 7 outer electrons (3s2 3p5), so it is in group VII: it is chlorine, a halogen.

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Question 7

Periodic Table

Beryllium and aluminium have similar properties because they

  1. A.are both metals.
  2. B.belong to the same group.
  3. C.belong to the same period.
  4. D.are positioned diagonally to each other.
Show the answer and explanation

Answer: D (are positioned diagonally to each other.)

Explanation

Beryllium (group II, period 2) and aluminium (group III, period 3) sit diagonally across the periodic table, and diagonal neighbours have similar charge density and so similar properties.

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Question 8

Chemical Bonding

If the difference in electronegativity of elements P and Q is 3.0, the bond that will be formed between them is

  1. A.metallic.
  2. B.covalent.
  3. C.co-ordinate.
  4. D.ionic.
Show the answer and explanation

Answer: D (ionic.)

Explanation

A large electronegativity difference (above about 1.7) means one atom takes electrons from the other, so the bond is ionic.

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Question 9

Atomic Structure

How many protons, neutrons and electrons respectively are present in the element 6027Co?

  1. A.27, 33 and 33.
  2. B.33, 27 and 27.
  3. C.27, 33 and 27.
  4. D.60, 33 and 60.
Show the answer and explanation

Answer: C (27, 33 and 27.)

Explanation

Protons = atomic number = 27; neutrons = 60 − 27 = 33; a neutral atom has as many electrons as protons, 27.

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Question 10

Chemical Bonding

The radioactive radiation used in studying the arrangement of particles in giant organic molecules is

  1. A.γ-rays.
  2. B.α-particles.
  3. C.X-rays.
  4. D.β-particles.
Show the answer and explanation

Answer: C (X-rays.)

Explanation

X-ray diffraction (crystallography) is used to work out how the atoms are arranged in large molecules and crystals.

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Question 11

Atomic Structure

A silicon-containing ore has 92% 28Si, 5% 29Si and 3% 30Si. Calculate the relative atomic mass of the silicon.

  1. A.14.00
  2. B.29.00
  3. C.28.11
  4. D.28.00
Show the answer and explanation

Answer: C (28.11)

Explanation

Relative atomic mass = (92 × 28 + 5 × 29 + 3 × 30)/100 = (2576 + 145 + 90)/100 = 28.11.

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Question 12

Air

The nitrogen obtained from air has a density higher than the one from nitrogen-containing compounds because the one from air is contaminated with

  1. A.water vapour.
  2. B.oxygen.
  3. C.rare gases.
  4. D.carbon(IV) oxide.
Show the answer and explanation

Answer: C (rare gases.)

Explanation

Nitrogen from air still contains the rare gases (mainly argon), which are denser than nitrogen, so it is slightly denser than pure nitrogen.

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Question 13

Water

Water is said to be temporarily hard when it contains

  1. A.Ca(HCO3)2 and Mg(HCO3)2 salts.
  2. B.Ca(HCO3)2 and CaCO3 salts.
  3. C.Mg(HCO3)2 and CaSO4 salts.
  4. D.CaSO4 and Ca(HCO3)2 salts.
Show the answer and explanation

Answer: A (Ca(HCO3)2 and Mg(HCO3)2 salts.)

Explanation

Temporary hardness is caused by dissolved calcium and magnesium hydrogentrioxocarbonates(IV), which boiling removes.

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Question 14

Water

On exposure to the atmosphere, a hydrated salt loses its water of crystallization to become anhydrous. This phenomenon is referred to as

  1. A.efflorescence.
  2. B.deliquescence.
  3. C.hygroscopy.
  4. D.hydrolysis.
Show the answer and explanation

Answer: A (efflorescence.)

Explanation

Efflorescent salts (e.g. washing soda) give up their water of crystallization to the air.

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Question 15

Solubility and Solutions

16.55 g of lead(II) trioxonitrate(V) was dissolved in 100 g of distilled water at 20 °C, calculate the solubility of the solute in mol dm-3. [Pb = 207, N = 14, O = 16]

  1. A.0.05 g
  2. B.2.00 g
  3. C.1.00 g
  4. D.0.50 g
Show the answer and explanation

Answer: D (0.50 g)

Explanation

Molar mass of Pb(NO3)2 = 207 + 2(14 + 48) = 331 g, so 16.55 g = 0.05 mol in 100 g of water. In 1000 g (about 1 dm3) that is 0.50 mol dm-3.

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Question 16

Solubility and Solutions

The dispersion of a liquid in a liquid medium will give

  1. A.an emulsion.
  2. B.a fog.
  3. C.a gel.
  4. D.an aerosol.
Show the answer and explanation

Answer: A (an emulsion.)

Explanation

An emulsion, such as milk, is one liquid spread as tiny drops through another liquid.

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Question 19

Acids, Bases and Salts

The colour of litmus in a neutral medium is

  1. A.purple
  2. B.pink
  3. C.yellow
  4. D.orange
Show the answer and explanation

Answer: A (purple)

Explanation

Litmus is red in acid and blue in alkali; in a neutral solution it shows the in-between colour, purple.

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Question 20

Acids, Bases and Salts

The mathematical expression of pH is

  1. A.log10[OH−]
  2. B.log10 1/[H3O+]
  3. C.log10[H3O+]
  4. D.log10 1/[OH−]
Show the answer and explanation

Answer: B (log10 1/[H3O+])

Explanation

pH = −log10[H3O+], which is the same as log10(1/[H3O+]).

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Question 21

Acids, Bases and Salts

Which of the following salts will turn blue litmus red?

  1. A.Sodium tetrahydroxozincate(II).
  2. B.Potassium hydrogentetraoxosulphate(VI).
  3. C.Sodium trioxocarbonate(IV).
  4. D.Zinc chloride hydroxide.
Show the answer and explanation

Answer: B (Potassium hydrogentetraoxosulphate(VI).)

Explanation

KHSO4 is an acid salt: its HSO4− ion releases H+ in water, so the solution is acidic and turns blue litmus red.

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Question 22

Redox Reactions

Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)
In the reaction above, the oxidation number of the reducing agent changes from

  1. A.0 to +4.
  2. B.0 to +2.
  3. C.+1 to +2.
  4. D.+1 to +3.
Show the answer and explanation

Answer: B (0 to +2.)

Explanation

Zinc is the reducing agent: it goes from the element (0) to Zn2+ in ZnSO4 (+2).

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Question 23

Redox Reactions

H2O(g) + C(s) → H2(g) + CO(g)
The oxidizing agent in the reaction above is

  1. A.CO(g)
  2. B.C(s)
  3. C.H2O(g)
  4. D.H2(g)
Show the answer and explanation

Answer: C (H2O(g))

Explanation

Steam gives its oxygen to carbon (hydrogen goes from +1 to 0), so water is reduced and is the oxidizing agent.

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Question 24

Electrolysis

Calculate the quantity of electricity in coulombs required to liberate 10 g of copper from a copper compound. [Cu = 64, F = 96500 C mol-1]

  1. A.32395.5
  2. B.30156.3
  3. C.60784.5
  4. D.15196.5
Show the answer and explanation

Answer: B (30156.3)

Explanation

Cu2+ + 2e− → Cu: 64 g needs 2 × 96500 C, so 10 g needs (10 × 2 × 96500)/64 = 30156.3 C.

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Question 25

Electrolysis

How many faraday of electricity is required to produce 0.25 mole of copper?

  1. A.1.00 F
  2. B.0.01 F
  3. C.0.05 F
  4. D.0.50 F
Show the answer and explanation

Answer: D (0.50 F)

Explanation

Each mole of Cu2+ needs 2 F, so 0.25 mol needs 0.25 × 2 = 0.50 F.

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Question 26

Energy Changes

Z in the diagram above represents

Diagram for this question
  1. A.heat of reaction.
  2. B.activation energy.
  3. C.free energy.
  4. D.entropy of reaction.
Show the answer and explanation

Answer: A (heat of reaction.)

Explanation

Z is the energy gap between the reactants (A + B) and the products (C + D), which is the heat of reaction ΔH.

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Question 27

Energy Changes

If the change in free energy of a system is −899 J mol-1 and the entropy change is 10 J mol-1 K-1 at 25 °C, calculate the enthalpy change.

  1. A.+2081 J mol-1
  2. B.−2081 J mol-1
  3. C.−649 J mol-1
  4. D.+649 J mol-1
Show the answer and explanation

Answer: A (+2081 J mol-1)

Explanation

ΔG = ΔH − TΔS, so ΔH = ΔG + TΔS = −899 + 298 × 10 = +2081 J mol-1.

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Question 28

Chemical Equilibrium

In an equilibrium reaction, which of the following conditions indicates that maximum yield of the product will be obtained?

  1. A.Equilibrium constant is very large.
  2. B.ΔH − TΔS = 0.
  3. C.ΔH > TΔS.
  4. D.Equilibrium constant is less than zero.
Show the answer and explanation

Answer: A (Equilibrium constant is very large.)

Explanation

A very large equilibrium constant means the equilibrium mixture is mostly products.

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Question 29

Rates of Reaction

In a chemical reaction, the change in concentration of a reactant with time is

  1. A.entropy of reaction.
  2. B.enthalpy of reaction.
  3. C.rate of reaction.
  4. D.order of reaction.
Show the answer and explanation

Answer: C (rate of reaction.)

Explanation

Rate of reaction is defined as how fast the concentration of a reactant (or product) changes with time.

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Question 30

Chemical Equilibrium

Cr2O72−(aq) + H2O(l) ⇌ 2CrO42−(aq) + 2H+(aq)
What happens to the reaction above when the hydrogen ion concentration is increased?

  1. A.More of the products will be formed.
  2. B.The reaction will not proceed.
  3. C.The equilibrium position will shift to the right.
  4. D.The equilibrium position will shift to the left.
Show the answer and explanation

Answer: D (The equilibrium position will shift to the left.)

Explanation

H+ is a product; adding more of it makes the equilibrium shift to the left to use it up (Le Chatelier's principle).

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Question 31

Metals and their Compounds

Which of the following will liberate hydrogen from dilute tetraoxosulphate(VI) acid?

  1. A.Lead.
  2. B.Magnesium.
  3. C.Copper.
  4. D.Gold.
Show the answer and explanation

Answer: B (Magnesium.)

Explanation

Magnesium is above hydrogen in the activity series and reacts readily with dilute acid; copper and gold do not, and lead is stopped by insoluble PbSO4.

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Question 32

Halogens

Use the diagram (preparation of chlorine) to answer this question.
In the diagram, the function of the concentrated H2SO4 is to

Diagram for this question
  1. A.purify the gas.
  2. B.dry the gas.
  3. C.liquefy the gas.
  4. D.remove odour.
Show the answer and explanation

Answer: B (dry the gas.)

Explanation

Concentrated tetraoxosulphate(VI) acid absorbs water, so the last bottle dries the chlorine.

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Question 33

Halogens

Use the diagram (preparation of chlorine) to answer this question.
The gas that is removed by the water in the flask is

Diagram for this question
  1. A.O2.
  2. B.SO2.
  3. C.HCl.
  4. D.H2.
Show the answer and explanation

Answer: C (HCl.)

Explanation

Hydrogen chloride fumes from the concentrated acid are very soluble in water, so the water bottle removes them from the chlorine.

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Question 34

Halogens

Fluorine does not occur in the free state in nature because

  1. A.it is a poisonous gas.
  2. B.it belongs to the halogen family.
  3. C.it is inert.
  4. D.of its high reactivity.
Show the answer and explanation

Answer: D (of its high reactivity.)

Explanation

Fluorine is the most reactive non-metal, so it is always found combined with other elements.

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Question 35

Metals and their Compounds

In the extraction of sodium from fused sodium chloride, the anode is made of platinum because

  1. A.sodium is formed at the anode.
  2. B.chlorine is formed at the anode.
  3. C.sodium does not react with platinum.
  4. D.chlorine does not react with platinum.
Show the answer and explanation

Answer: D (chlorine does not react with platinum.)

Explanation

Chlorine is released at the anode and attacks most metals, so the anode is made of an inert material that chlorine does not react with.

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Question 36

Qualitative Analysis

A compound that gives a brick-red colour to a non-luminous flame is likely to contain

  1. A.copper ions.
  2. B.sodium ions.
  3. C.calcium ions.
  4. D.aluminium ions.
Show the answer and explanation

Answer: C (calcium ions.)

Explanation

Calcium ions give a brick-red flame; sodium gives yellow and copper gives green-blue.

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Question 37

Metals and their Compounds

In the electrolytic extraction of calcium from calcium chloride, the cathode is

  1. A.zinc.
  2. B.graphite.
  3. C.platinum.
  4. D.iron.
Show the answer and explanation

Answer: D (iron.)

Explanation

In the industrial cell the anode is graphite and the cathode, where calcium collects, is iron.

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Question 38

Qualitative Analysis

A few drops of NaOH solution was added to an unknown salt forming a white precipitate which is insoluble in excess solution. The cation likely present is

  1. A.Zn2+.
  2. B.Pb2+.
  3. C.Ca2+.
  4. D.Al3+.
Show the answer and explanation

Answer: C (Ca2+.)

Explanation

Zn2+, Pb2+ and Al3+ hydroxides are amphoteric and dissolve in excess NaOH; Ca(OH)2 stays as a white precipitate.

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Question 39

Introduction to Organic Chemistry

The general formula of haloalkanes where X represents the halide is

  1. A.CnH2n−1X.
  2. B.CnH2nX.
  3. C.CnH2n+2X.
  4. D.CnH2n+1X.
Show the answer and explanation

Answer: D (CnH2n+1X.)

Explanation

A haloalkane is an alkane (CnH2n+2) with one H replaced by a halogen: CnH2n+1X.

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Question 40

Introduction to Organic Chemistry

The IUPAC nomenclature of the compound above is

Diagram for this question
  1. A.2-bromo-3-chlorobutanol.
  2. B.3-bromo-2-chlorobutanol.
  3. C.3-chloro-2-bromobutanol.
  4. D.2-chloro-3-bromobutanol.
Show the answer and explanation

Answer: B (3-bromo-2-chlorobutanol.)

Explanation

Number from the carbon with –OH (C1): Cl is on C2 and Br on C3. Prefixes go in alphabetical order, so the name is 3-bromo-2-chlorobutanol.

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Question 42

Hydrocarbons

Ethyne is passed through a hot tube containing organo-nickel catalyst to produce

  1. A.isoprene.
  2. B.polythene.
  3. C.ethanol.
  4. D.benzene.
Show the answer and explanation

Answer: D (benzene.)

Explanation

Three ethyne molecules join into a ring (polymerise) over the hot catalyst to form benzene, C6H6.

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Question 43

Hydrocarbons

Due to the unstable nature of ethyne, it is stored by dissolving in

  1. A.ethane-1,2-diol.
  2. B.propanol.
  3. C.ethanoic acid.
  4. D.propanone.
Show the answer and explanation

Answer: D (propanone.)

Explanation

Ethyne can explode under pressure, so cylinders hold it dissolved in propanone (acetone).

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Question 44

Carbohydrates, Proteins and Amines

The process of converting starch to ethanol is

  1. A.cracking.
  2. B.distillation.
  3. C.fermentation.
  4. D.oxidation.
Show the answer and explanation

Answer: C (fermentation.)

Explanation

Yeast enzymes break starch down to sugars and then to ethanol and carbon(IV) oxide: fermentation.

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Question 45

Polymers

The polymer used in making car rear lights is

  1. A.perspex.
  2. B.bakelite.
  3. C.polystyrene.
  4. D.polyacrylonitrile.
Show the answer and explanation

Answer: A (perspex.)

Explanation

Perspex is a clear, tough plastic that can be coloured, so it is used for car light covers.

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Question 46

Alkanoic Acids and Esters

CH3COOC2H5(l) + H2O(l) ⇌ CH3COOH(aq) + C2H5OH(aq)
The purpose of H+ in the reaction above is to

  1. A.increase the yield of products.
  2. B.maintain the solution at a constant pH.
  3. C.increase the rate of hydrolysis.
  4. D.decrease the rate of the reverse reaction.
Show the answer and explanation

Answer: C (increase the rate of hydrolysis.)

Explanation

The acid acts as a catalyst: it speeds up the hydrolysis of the ester but does not shift the equilibrium.

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Question 47

Introduction to Organic Chemistry

A hydrocarbon has an empirical formula CH and a vapour density of 39. Determine its molecular formula. [C = 12, H = 1]

  1. A.C2H6
  2. B.C3H8
  3. C.C3H4
  4. D.C6H6
Show the answer and explanation

Answer: D (C6H6)

Explanation

Molar mass = 2 × 39 = 78. (CH)n: 13n = 78, so n = 6 and the formula is C6H6.

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Question 48

Polymers

Polystyrene is widely used as packaging materials for fragile objects during transportation because of its

  1. A.lightness.
  2. B.low density.
  3. C.high density.
  4. D.high compressibility.
Show the answer and explanation

Answer: B (low density.)

Explanation

Expanded polystyrene is mostly trapped air, so its very low density makes it a light, cushioning packing material.

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Question 49

Petroleum and Coal

The process of converting linear alkanes to branched chain and cyclic hydrocarbons by heating in the presence of a catalyst to improve the quality of petrol is referred to as

  1. A.refining.
  2. B.cracking.
  3. C.reforming.
  4. D.blending.
Show the answer and explanation

Answer: C (reforming.)

Explanation

Reforming rearranges straight-chain alkanes into branched and ring compounds, which raises the octane rating of petrol.

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Question 50

Petroleum and Coal

The petroleum fraction that is used in heating furnaces in industries is

  1. A.diesel oil.
  2. B.gasoline.
  3. C.kerosene.
  4. D.lubricating oil.
Show the answer and explanation

Answer: A (diesel oil.)

Explanation

Diesel (gas) oil and heavier fuel oils are burnt in industrial furnaces and boilers.

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