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JAMB Chemistry 2009 past questions and answers

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

Question 1

Separation of Mixtures

A mixture of sugar and sulphur can be separated by

  1. A.dissolution in water, evaporation and filtration
  2. B.filtration, evaporation and dissolution in water
  3. C.dissolution in water, filtration and evaporation
  4. D.evaporation, dissolution in water and filtration
Show the answer and explanation

Answer: C (dissolution in water, filtration and evaporation)

Explanation

Sugar dissolves in water but sulphur does not. Dissolve, filter off the sulphur, then evaporate the filtrate to recover the sugar.

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Question 3

Mole Concept and Stoichiometry

The percentage of water of crystallization in ZnSO4.7H2O is [Zn = 65, S = 32, O = 16, H = 1]

  1. A.33%
  2. B.44%
  3. C.55%
  4. D.87%
Show the answer and explanation

Answer: B (44%)

Explanation

Molar mass = 65 + 32 + 64 + 7(18) = 287. Water = 126, so 126/287 × 100 ≈ 44%.

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Question 4

Mole Concept and Stoichiometry

0.0075 mole of calcium trioxocarbonate(IV) is added to 0.015 mole of a solution of hydrochloric acid. The volume of gas evolved at s.t.p. is [Molar volume of a gas at s.t.p. = 22.4 dm3]

  1. A.224 cm3
  2. B.168 cm3
  3. C.112 cm3
  4. D.100 cm3
Show the answer and explanation

Answer: B (168 cm3)

Explanation

CaCO3 + 2HCl → CaCl2 + H2O + CO2. 0.0075 mol CaCO3 uses exactly 0.015 mol HCl and gives 0.0075 mol CO2 = 0.0075 × 22 400 = 168 cm3.

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Question 6

Gas Laws

The basic assumption in the kinetic theory of gases that the collisions of the gaseous molecules are perfectly elastic implies that the

  1. A.forces of attraction and repulsion are in equilibrium
  2. B.gaseous molecules can occupy any available space
  3. C.gaseous molecules will continue their motion indefinitely
  4. D.gases can be compressed
Show the answer and explanation

Answer: C (gaseous molecules will continue their motion indefinitely)

Explanation

In a perfectly elastic collision no kinetic energy is lost, so the molecules never slow down and keep moving.

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Question 7

Atomic Structure

If an atom is represented as 2311X, which of the following deductions is correct?

  1. A.It contains 12 protons
  2. B.It forms a covalent chloride
  3. C.Its atomic number is 23
  4. D.It is an alkali metal
Show the answer and explanation

Answer: D (It is an alkali metal)

Explanation

Atomic number 11 is sodium (2,8,1), a group 1 alkali metal. It has 11 protons and 12 neutrons.

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Question 8

Atomic Structure

If the relative molecular mass of an element is not a whole number, it can be deduced that the element is

  1. A.naturally radioactive
  2. B.abundant in nature
  3. C.a transition metal
  4. D.an isotopic mixture
Show the answer and explanation

Answer: D (an isotopic mixture)

Explanation

A fractional relative atomic mass is the average of the masses of its isotopes weighted by their abundance.

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Question 9

Atomic Structure

Cathode rays cause an object placed behind a perforated anode to cast a shadow on the screen. This observation shows that the rays

  1. A.are positively charged
  2. B.are negatively charged
  3. C.have mass
  4. D.travel in straight lines
Show the answer and explanation

Answer: D (travel in straight lines)

Explanation

A sharp shadow forms only if the rays travel in straight lines past the object.

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Question 10

Atomic Structure

Which quantum number divides shells into orbitals?

  1. A.Principal
  2. B.Azimuthal
  3. C.Magnetic
  4. D.Spin
Show the answer and explanation

Answer: B (Azimuthal)

Explanation

The azimuthal (subsidiary) quantum number splits each main shell into s, p, d and f sub-levels (orbital types).

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Question 11

Chemical Bonding

The type of bonding in [Cu(NH3)4]2+ is

  1. A.coordinate
  2. B.electrovalent
  3. C.metallic
  4. D.covalent
Show the answer and explanation

Answer: A (coordinate)

Explanation

Each NH3 donates its lone pair to the Cu2+ ion, forming dative (coordinate) bonds.

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Question 12

Air

The mixture of gases used in a photographer's flash tube is

  1. A.argon and krypton
  2. B.krypton and xenon
  3. C.helium and argon
  4. D.argon and xenon
Show the answer and explanation

Answer: B (krypton and xenon)

Explanation

Photographic flash tubes are filled with the heavier noble gases krypton and xenon, which give an intense white flash.

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Question 13

Water

When sodium trioxocarbonate (IV) decahydrate loses its water of crystallization to the atmosphere, the process is

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

Answer: B (efflorescence)

Explanation

Losing water of crystallization to the air is called efflorescence.

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Question 14

Hydrogen, Oxygen and Oxides

Water can be obtained as the only product during the

  1. A.combustion of hydrocarbons
  2. B.neutralization of an acid by a base
  3. C.combustion of hydrogen
  4. D.electrolysis of brine
Show the answer and explanation

Answer: C (combustion of hydrogen)

Explanation

2H2 + O2 → 2H2O gives water alone; hydrocarbons also give CO2 and neutralization also gives a salt.

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Question 15

Solubility and Solutions

If 10.5g of lead (II) trioxonitrate (V) is dissolved in 20cm3 of distilled water at 180C, the solubility of the solute in mol dm−3 is [Pb = 207, N = 14, O = 16]

  1. A.1.60
  2. B.5.25
  3. C.16.00
  4. D.525.00
Show the answer and explanation

Answer: A (1.60)

Explanation

Pb(NO3)2 = 331 g/mol, so 10.5 g = 0.0317 mol. In 1000 cm3: 0.0317 × 1000/20 ≈ 1.60 mol dm−3.

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Question 16

Solubility and Solutions

For a given solute, the concentration of its saturated solution in different solvents are

  1. A.the same at the same temperature
  2. B.different at the same temperature
  3. C.the same at different temperatures
  4. D.constant
Show the answer and explanation

Answer: B (different at the same temperature)

Explanation

Solubility depends on the solvent, so a solute's saturated concentration differs from one solvent to another even at the same temperature.

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Question 18

Electrolysis

The acid used in electrolysis of water is dilute

  1. A.HNO3
  2. B.CH3COOH
  3. C.H2SO4
  4. D.HCl
Show the answer and explanation

Answer: C (H2SO4)

Explanation

Dilute H2SO4 makes water conduct; its sulphate ions are not discharged, so only H2 and O2 are produced.

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Question 19

Mole Concept and Stoichiometry

What volume of 1.5 M solution of KOH would contain 0.045 moles?

  1. A.67.50cm3
  2. B.30.00cm3
  3. C.6.75cm3
  4. D.3.00cm3
Show the answer and explanation

Answer: B (30.00cm3)

Explanation

Volume = moles ÷ concentration = 0.045/1.5 = 0.030 dm3 = 30 cm3.

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Question 20

Acids, Bases and Salts

The salt formed from a reaction between citric acid and sodium hydroxide in solution will be

  1. A.acidic
  2. B.basic
  3. C.complex
  4. D.neutral
Show the answer and explanation

Answer: B (basic)

Explanation

A weak acid with a strong base gives a salt that hydrolyses to make the solution slightly alkaline.

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Question 21

Redox Reactions

The colour change observed when testing for reducing agents using acidified potassium heptaoxodichromate (VI) solution is

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

Answer: B (orange to green)

Explanation

A reducing agent turns orange Cr2O72− into green Cr3+.

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Question 22

Redox Reactions

The oxidation state of Cr in K2Cr2O7 is

  1. A.+7
  2. B.+6
  3. C.+5
  4. D.4
Show the answer and explanation

Answer: B (+6)

Explanation

2(+1) + 2x + 7(−2) = 0, so 2x = 12 and x = +6.

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Question 23

Electrolysis

Which of the following metals is purified commercially by eletrolysis?

  1. A.Zn
  2. B.Fe
  3. C.Sn
  4. D.Cu
Show the answer and explanation

Answer: D (Cu)

Explanation

Impure copper is made the anode and pure copper deposits on the cathode during electrolytic refining.

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Question 24

Electrolysis

What current will deposit 3.25g of zinc in 2 hrs? [Zn = 65, F = 96500 mol−1]

  1. A.3.25A
  2. B.2.00A
  3. C.1.34A
  4. D.0.67A
Show the answer and explanation

Answer: C (1.34A)

Explanation

3.25/65 = 0.05 mol Zn needs 2 × 0.05 = 0.1 F = 9650 C. I = 9650/7200 s ≈ 1.34 A.

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Question 25

Energy Changes

C(s) + H2O(g) → H2(g) + CO(g)
ΔG for the reaction above at 1300K is −43KJ. At this temperature, the reaction is

  1. A.not feasible
  2. B.at equilibrium
  3. C.feasible
  4. D.exothermic
Show the answer and explanation

Answer: C (feasible)

Explanation

A negative ΔG means the reaction is spontaneous (feasible) at that temperature.

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Question 26

Energy Changes

Two equal bulbs, one containing ammonia and the other nitrogen, are opened mouth-to-mouth to each other at room temperature. The entropy in the mixture of gases is likely to

  1. A.remain unchanged
  2. B.increase
  3. C.decrease
  4. D.change
Show the answer and explanation

Answer: B (increase)

Explanation

The gases diffuse and mix, which increases disorder, so entropy increases.

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Question 27

Rates of Reaction

In the diagram above, which of the curves represents the evolution of oxygen with time in the equation 2KClO3(s) → 2KCl(s) + 3O2(g)?

Diagram for this question
  1. A.X
  2. B.Y
  3. C.Z
  4. D.R
Show the answer and explanation

Answer: D (R)

Explanation

The volume of oxygen starts at zero, rises quickly, then levels off when all the KClO3 has decomposed, which is curve R.

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Question 28

Rates of Reaction

A catalyst increases the rate of a chemical reaction by providing a path that

  1. A.raises the activation energy
  2. B.increases the temperature
  3. C.lowers the activation energy
  4. D.increases the concentration
Show the answer and explanation

Answer: C (lowers the activation energy)

Explanation

A catalyst offers an alternative route with lower activation energy, so more collisions succeed.

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Question 29

Chemical Equilibrium

CuO(s) + H2(g) ⇌ Cu(s) + H2O(l)
What is the effect of increasing the pressure on the equilibrium reaction above?

  1. A.The equilibrium is shifted to the left
  2. B.The equilibrium is shifted to the right
  3. C.There is no effect
  4. D.More H2(g) is produced
Show the answer and explanation

Answer: B (The equilibrium is shifted to the right)

Explanation

As written, the only gas is H2 on the left. Increasing pressure favours the side with fewer gas molecules, which is the right.

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Question 30

Chemical Equilibrium

The equilibrium of an endothermic reaction which proceeds with an increase in volume can be shifted in the reverse direction by

  1. A.increasing the temperature and decreasing the pressure
  2. B.increasing the pressure and increasing the temperature
  3. C.decreasing the temperature and increasing the pressure
  4. D.decreasing the pressure and decreasing the temperature
Show the answer and explanation

Answer: C (decreasing the temperature and increasing the pressure)

Explanation

Lowering temperature opposes an endothermic forward reaction, and raising pressure favours the side with smaller volume (the reactants).

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Question 31

Nitrogen and its Compounds

The oxidation of ammonia in excess air produces

  1. A.NO
  2. B.N2O
  3. C.NO2
  4. D.N2O4
Show the answer and explanation

Answer: A (NO)

Explanation

Catalytic oxidation of ammonia gives nitrogen(II) oxide: 4NH3 + 5O2 → 4NO + 6H2O.

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Question 32

Sulphur and its Compounds

Hydrogen sulphide gas can act as

  1. A.an oxidizing agent
  2. B.a dehydrating agent
  3. C.a bleaching agent
  4. D.a precipitating agent
Show the answer and explanation

Answer: D (a precipitating agent)

Explanation

H2S precipitates many metal ions as insoluble sulphides (it is used this way in qualitative analysis).

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Question 33

Petroleum and Coal

The gasification of coke is used for the manufacture of

  1. A.producer gas
  2. B.natural gas
  3. C.synthetic gas
  4. D.industrial gas
Show the answer and explanation

Answer: A (producer gas)

Explanation

Passing air over red-hot coke converts it into producer gas (CO and N2).

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Question 34

Environmental Pollution

The gas that is most useful in protecting humans against solar radiations is

  1. A.chlorine
  2. B.ozone
  3. C.carbon(IV) oxide
  4. D.hydrogen sulphide
Show the answer and explanation

Answer: B (ozone)

Explanation

The ozone layer absorbs most of the sun's harmful ultraviolet radiation.

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Question 35

Carbon and its Compounds

Which of the allotrope of carbon is a constituent of a lead pencil?

  1. A.Graphite
  2. B.Diamond
  3. C.Lampblack
  4. D.Soot
Show the answer and explanation

Answer: A (Graphite)

Explanation

Pencil 'lead' is graphite mixed with clay; graphite is soft and leaves a mark.

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Question 36

Periodic Table

Which of the following metals will show the highest metallic character?

  1. A.Zinc
  2. B.Copper
  3. C.Barium
  4. D.Calcium
Show the answer and explanation

Answer: C (Barium)

Explanation

Metallic character increases down a group, so barium (below calcium in group 2) loses electrons most easily.

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Question 37

Nitrogen and its Compounds

Copper metal dissolves in concentrated trioxonitrate (V) acid with the resultant evolution of

  1. A.CO2
  2. B.SO2
  3. C.NO2
  4. D.CO
Show the answer and explanation

Answer: C (NO2)

Explanation

Cu + 4HNO3 (conc.) → Cu(NO3)2 + 2NO2 + 2H2O; brown NO2 is given off.

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Question 38

Metals and their Compounds

The type of iron that is best suited for welding, making nails, chains and iron rods is

  1. A.pig iron
  2. B.wrought iron
  3. C.cast iron
  4. D.iron pyrites
Show the answer and explanation

Answer: B (wrought iron)

Explanation

Wrought iron is almost pure iron, so it is malleable and easy to weld and shape.

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Question 39

Metals and their Compounds

In the electrolytic extraction of aluminium, the function of the molten cryolite is to

  1. A.precipitate aluminium hydroxide
  2. B.lower the melting point of aluminium oxide
  3. C.act as a raw material
  4. D.act as a solvent
Show the answer and explanation

Answer: B (lower the melting point of aluminium oxide)

Explanation

Alumina melts above 2000 °C; dissolving it in cryolite lowers the working temperature to about 950 °C, saving energy.

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Question 40

Nitrogen and its Compounds

One of the products of the thermal decomposition of sodium trioxonitrate (V) is

  1. A.sodium
  2. B.nitrogen
  3. C.sodium dioxonitrate (III)
  4. D.sodium oxide
Show the answer and explanation

Answer: C (sodium dioxonitrate (III))

Explanation

2NaNO3 → 2NaNO2 + O2; group 1 nitrates give the nitrite (dioxonitrate(III)) and oxygen.

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Question 41

Petroleum and Coal

A cracking process in petroleum refining can be represented by

  1. A.heptane to heptene
  2. B.heptane to 3-methylhexane
  3. C.heptane to propene and butane
  4. D.heptane to 2,3,3-trimethybutane
Show the answer and explanation

Answer: C (heptane to propene and butane)

Explanation

Cracking breaks a large molecule into smaller ones: C7H16 → C3H6 + C4H10.

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Question 43

Carbohydrates, Proteins and Amines

Which of the following class of compounds can exist as dipolar ions in solution?

  1. A.Alkanoic acids
  2. B.Fatty acids
  3. C.Dialkanoic acids
  4. D.Amino acids
Show the answer and explanation

Answer: D (Amino acids)

Explanation

An amino acid has both −NH2 and −COOH groups, so it forms a zwitterion (+H3N−CHR−COO−).

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Question 44

Alkanols

Lucas reagent is used to test for

  1. A.alkanes
  2. B.alkanoic acids
  3. C.alkanols
  4. D.amines
Show the answer and explanation

Answer: C (alkanols)

Explanation

Lucas reagent (ZnCl2 in conc. HCl) distinguishes primary, secondary and tertiary alkanols by how fast cloudiness appears.

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Question 45

Alkanols

A compound commonly used for sterilization and preservation of specimens and food is

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

Answer: A (ethanol)

Explanation

Ethanol kills microbes, so it is used as an antiseptic and to preserve biological specimens.

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Question 47

Hydrocarbons

Which of the following hydrocarbons is mainly used as fuel?

  1. A.Methylene
  2. B.Ethylene
  3. C.Methane
  4. D.Ethyne
Show the answer and explanation

Answer: C (Methane)

Explanation

Methane is the main part of natural gas, used as a fuel for cooking and heating.

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Question 48

Hydrocarbons

The molecular formula of a common organic laboratory anaesthetic is

  1. A.CHCl3
  2. B.CHI3
  3. C.CCl4
  4. D.CHF3
Show the answer and explanation

Answer: A (CHCl3)

Explanation

Trichloromethane (chloroform), CHCl3, was a common anaesthetic.

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Question 49

Hydrocarbons

The simplest branched-chain hydrocarbon is

  1. A.ethane
  2. B.ethene
  3. C.propane
  4. D.butane
Show the answer and explanation

Answer: D (butane)

Explanation

A branch needs at least four carbons: 2-methylpropane is an isomer of butane.

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Question 50

Hydrocarbons

Organic molecules that have the suffix-ene are unsaturated hydrocarbons that have

  1. A.a single bond
  2. B.a double bond
  3. C.a triple bond
  4. D.an ionic bond
Show the answer and explanation

Answer: B (a double bond)

Explanation

The ending -ene shows an alkene, which contains a C=C double bond.

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