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JAMB Chemistry 1979 past questions and answers

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

Question 1

Alkanoic Acids and Esters

An organic compound X has the following properties: I. It is not miscible with water. II. It has boiling point of 77°C III. It has a sweet odour IV. It is insoluble in sodium hydrogen carbonate solution V. It does not decolourize bromine water. X is therefore

  1. A.methane
  2. B.ethanoic acid
  3. C.ethene
  4. D.ethyl ethanoate
  5. E.carbon tetrachloride.
Show the answer and explanation

Answer: D (ethyl ethanoate)

Explanation

A sweet (fruity) smelling, water-insoluble liquid boiling at 77°C that is not an acid (no reaction with NaHCO3) and not unsaturated (no effect on bromine water) is the ester ethyl ethanoate.

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Question 2

Introduction to Organic Chemistry

Which are the correct IUPAC names for H-CO2CH3 and CH ≡ CH

  1. A.Methyl methanoate and ethene
  2. B.Metanoic acid and ethyne
  3. C.Ethyl methanoate and ethyne
  4. D.Methyl methanoate and ethyne
  5. E.Ethanoic acid and ethene.
Show the answer and explanation

Answer: D (Methyl methanoate and ethyne)

Explanation

HCOOCH3 is the ester of methanoic acid and methanol, methyl methanoate. CH≡CH has a triple bond, so it is ethyne.

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Question 3

Polymers

Which of the following substances are all made by the process of polymerization?

  1. A.Nylon and soap.
  2. B.Ethanoic acid, margarine and ethanol
  3. C.Nylon and artificial rubber
  4. D.Soap and butane
  5. E.Margarine and nylon.
Show the answer and explanation

Answer: C (Nylon and artificial rubber)

Explanation

Nylon and synthetic rubber are both made by joining many small monomer molecules into long chains. Soap is made by saponification and margarine by hydrogenation.

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Question 4

Redox Reactions

The reaction of zinc with copper (II) ions in aqueous solution can be represented as follows: Cu2+(aq) + Zn(s) → Cu(s) + Zn2+(aq). Which of the following is the most complete description of this reaction?

  1. A.Copper (II) ions are being reduced.
  2. B.Zinc is being oxidized.
  3. C.Copper (II) ions and zinc are being reduced.
  4. D.Copper (II) ions and zinc are being oxidized
  5. E.Copper (II) ions are being reduced and zinc oxidized.
Show the answer and explanation

Answer: E (Copper (II) ions are being reduced and zinc oxidized.)

Explanation

Cu2+ gains two electrons (reduced) while Zn loses two electrons (oxidised). Only E describes both halves of the redox reaction.

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Question 5

Redox Reactions

The oxidation state of manganese in potassium permanganate is

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

Answer: A (+7)

Explanation

In KMnO4: (+1) + x + 4(−2) = 0, so x = +7.

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Question 6

Carbon and its Compounds

When carbondioxide is bubbled into limewater a white precipitate is formed. If the passage of the gas is continued the precipitate disappears. The reason for this is

  1. A.calcium carbonate is formed which on reaction dissolves
  2. B.calcium hydrogen carbonate is precipitated and then dissolves
  3. C.calcium carbonate is formed which on reaction with further carbondioxide forms soluble calcium hydrogen carbonate
  4. D.concentration of the solution has occurred with the deposition of calcium hydroxide
  5. E.the solution has become saturated and solid carbondioxide has been deposited.
Show the answer and explanation

Answer: C (calcium carbonate is formed which on reaction with further carbondioxide forms soluble calcium hydrogen carbonate)

Explanation

The white precipitate is CaCO3. Excess CO2 and water convert it to calcium hydrogen carbonate, Ca(HCO3)2, which is soluble.

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Question 7

Chemical Equilibrium

The following reactions are stages in important industrial processes: I. N2(g) + 3H2(g) ⇌ 2NH3(g) ΔH is negative II. 2SO2(g) + O2(g) ⇌ 2SO3(g) ΔH is negative III. N2(g) + O2(g) ⇌ 2NO(g) ΔH is positive. Which of the above forward reactions is favoured by (i) a decrease in the concentration of the pressure and (ii) an increase in temperature?

  1. A.I
  2. B.II
  3. C.III
  4. D.I and II
  5. E.I and III
Show the answer and explanation

Answer: C (III)

Explanation

Only III is endothermic, so only it is helped by a rise in temperature. It has 2 moles of gas on each side, so lowering the pressure does not work against it, whereas I and II (fewer moles on the right) are favoured by high pressure.

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Question 8

Introduction to Organic Chemistry

The IUPAC name for CH3–CH(CH3)–CH = CH2 is

  1. A.2-methylbut-3-ene
  2. B.2-methylbut-4-ene
  3. C.3-methylbut-2-ene
  4. D.3-methylbut-1-ene
  5. E.3-methylpent-1-ene.
Show the answer and explanation

Answer: D (3-methylbut-1-ene)

Explanation

The longest chain has 4 carbons with the double bond; numbering from the double-bond end puts it at C1 and the methyl group on C3: 3-methylbut-1-ene.

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Question 9

Separation of Mixtures

Methanoic acid mixes with water in all proportions and has about the same boiling point as water. Which of the following methods would you adopt to obtain pure water from a mixture of sand, water and methanoic acid?

  1. A.Fractional distillation
  2. B.Filtration followed by distillation
  3. C.Neutralization with sodium hydroxide followed by distillation
  4. D.Neutralization with sodium hydroxide followed by filtration
  5. E.Esterification with ethanol followed by distillation.
Show the answer and explanation

Answer: C (Neutralization with sodium hydroxide followed by distillation)

Explanation

Because the acid boils at almost the same temperature as water, distillation alone cannot separate them. Neutralising turns the acid into sodium methanoate, a non-volatile salt, so distilling then gives pure water and leaves the salt and sand behind.

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Question 10

Electrolysis

Which of the following statements applies during the electrolysis of sodium hydroxide solution using platinum electrodes?

  1. A.Na+ ions are discharged at the cathode
  2. B.Hydrogen ions are discharged at the anode
  3. C.The concentration of sodium hydroxide decreases at both electrode compartments
  4. D.The concentration of sodium hydroxide increases at the cathode only.
  5. E.The concentration of sodium hydroxide increases at the anode only.
Show the answer and explanation

Answer: D (The concentration of sodium hydroxide increases at the cathode only.)

Explanation

At the cathode, hydrogen is released from water, leaving extra OH− with the Na+, so NaOH becomes more concentrated there. At the anode OH− ions are discharged as oxygen, so it gets weaker there.

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Question 11

Atomic Structure

Which of the following statements is true? When the potassium atom forms its ion

  1. A.it gains one electron and becomes neutral
  2. B.its atomic number decreases
  3. C.it achieves electronic configuration of argon
  4. D.it loses one proton
  5. E.it loses one neutron.
Show the answer and explanation

Answer: C (it achieves electronic configuration of argon)

Explanation

Potassium (2,8,8,1) loses its single outer electron to become K+ (2,8,8), the same arrangement as argon. Its protons and neutrons do not change.

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Question 12

Hydrogen, Oxygen and Oxides

Which of the following contains two amphoteric oxides?

  1. A.Sodium oxide, Zinc oxide, Magnesium oxide
  2. B.Aluminium oxide, Calcium oxide, Zinc oxide
  3. C.Potassium oxide, Lithium oxide, Carbondioxide
  4. D.Silver oxide, Lead oxide, Sodium oxide
  5. E.Sulphur dioxide, Aluminium oxide, Carbon monoxide.
Show the answer and explanation

Answer: B (Aluminium oxide, Calcium oxide, Zinc oxide)

Explanation

Aluminium oxide and zinc oxide both react with acids and with alkalis, so they are amphoteric; calcium oxide is basic. Each other set has at most one amphoteric oxide.

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Question 13

Atomic Structure

Helium atoms are chemically unreactive because

  1. A.there are no electrons around the nucleus
  2. B.the number of protons equals the number of electrons
  3. C.there are equal number of protons and neutrons in the nucleus
  4. D.the outer electron shell is completely filled
  5. E.the atoms contain only protons.
Show the answer and explanation

Answer: D (the outer electron shell is completely filled)

Explanation

Helium's only shell holds 2 electrons and is full (a duplet), so the atom has no tendency to gain, lose or share electrons.

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Question 14

Gas Laws

50cm3 of hydrogen are sparked with 20cm3 of oxygen at 100°C and 1 atmosphere. The total volume of the residual gases in

  1. A.50 cm3
  2. B.10cm3
  3. C.40cm3
  4. D.30cm3
  5. E.70 cm3.
Show the answer and explanation

Answer: A (50 cm3)

Explanation

2H2 + O2 → 2H2O. 20 cm3 O2 uses 40 cm3 H2 and gives 40 cm3 steam (a gas at 100°C). Left: 10 cm3 H2 + 40 cm3 steam = 50 cm3.

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Question 15

Mole Concept and Stoichiometry

How many grams of HBr would exactly be required to react with 2 g of propyne? (C = 12, H = 1, Br = 80)

  1. A.4.1 g
  2. B.6.1 g
  3. C.8.1 g
  4. D.10.1g
  5. E.16.2g
Show the answer and explanation

Answer: C (8.1 g)

Explanation

Propyne C3H4 (40 g/mol) adds 2 HBr across its triple bond. 2 g = 0.05 mol, which needs 0.10 mol HBr = 0.10 × 81 = 8.1 g.

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Question 16

Metals and their Compounds

When ammonium, potassium and calcium carbonates are each separately heated

  1. A.none of them will decompose
  2. B.each of them will decompose to give carbondioxide and the respective oxide
  3. C.ammonium carbonate and potassium carbonate will not decompose
  4. D.only ammonium carbonate and calcium carbonate will decompose to carbondioxide and the respective oxide
  5. E.ammonium carbonate will decompose to give carbondioxide, water and ammonia.
Show the answer and explanation

Answer: E (ammonium carbonate will decompose to give carbondioxide, water and ammonia.)

Explanation

On heating, (NH4)2CO3 → 2NH3 + H2O + CO2. Calcium carbonate gives CaO and CO2, but potassium carbonate does not decompose, and ammonium carbonate gives no oxide.

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Question 17

Alkanoic Acids and Esters

The structural formula of ethanoic acid is

  1. A.H–C(=O)–OH
  2. B.CH3–C(=O)–H
  3. C.CH3–CH2–C(=O)–H
  4. D.CH3–CH2–C(=O)–OH
  5. E.CH3–C(=O)–OH
Show the answer and explanation

Answer: E (CH3–C(=O)–OH)

Explanation

Ethanoic acid has two carbons and the –COOH group: CH3COOH. A is methanoic acid, B and C are aldehydes and D is propanoic acid.

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Question 18

Halogens

If chlorine gas is bubbled into water and then this yellowish-green coloured solution is exposed to bright sunlight for a while:

  1. A.the solution will give out chlorine gas and hydrogen chloride gas
  2. B.the solution will produce chlorine gas and oxygen
  3. C.the solution will give out oxygen thereby producing hypochlorous acid
  4. D.the solution will give out oxygen gas leaving behind aqueous hydrochloric acid
  5. E.the solution is decomposed, giving out oxygen, hydrogen and chlorine.
Show the answer and explanation

Answer: D (the solution will give out oxygen gas leaving behind aqueous hydrochloric acid)

Explanation

Chlorine water contains HOCl, which sunlight decomposes: 2HOCl → 2HCl + O2. Oxygen is given off and hydrochloric acid remains.

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Question 19

Solubility and Solutions

12 g of solid potassium chlorate (KClO3) were added to 40 g of water and heated to dissolve all the solid. As the solution cools, crystals of potassium chlorate started forming at 66°C. The solubility of potassium chlorate at 66°C is therefore

  1. A.66
  2. B.33
  3. C.10
  4. D.20
  5. E.30
Show the answer and explanation

Answer: E (30)

Explanation

Crystals start forming when the solution is just saturated, so 12 g dissolve in 40 g water at 66°C. Per 100 g water: 12 × 100/40 = 30 g.

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Question 20

Electrolysis

In the electrolysis of dilute sulphuric acid using platinum electrodes, the products obtained at the anode and cathode are:

  1. A.Anode: Sulphur; Cathode: hydrogen
  2. B.Anode: Hydrogen; Cathode: oxygen
  3. C.Anode: Oxygen; Cathode: hydrogen
  4. D.Anode: Hydrogen; Cathode: sulphate ions
  5. E.Anode: Sulphur; Cathode: oxygen
Show the answer and explanation

Answer: C (Anode: Oxygen; Cathode: hydrogen)

Explanation

OH− ions are discharged at the anode as oxygen and H+ ions at the cathode as hydrogen; in effect water is electrolysed.

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Question 21

Chemical Formulae and Equations

The empirical formula of an oxide of nitrogen containing 30.4 per cent of nitrogen is (N = 14.0, O = 16.0)

  1. A.N2O2
  2. B.NO
  3. C.NO2
  4. D.N2O
  5. E.N2O3.
Show the answer and explanation

Answer: C (NO2)

Explanation

N: 30.4/14 = 2.17; O: 69.6/16 = 4.35. Dividing by 2.17 gives N:O = 1:2, so NO2.

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Question 22

Air

When a piece of charcoal enclosed in a cylinder containing air is ignited

  1. A.the total volume of air is increased
  2. B.the relative amount of oxygen present is increased
  3. C.the relative amount of nitrogen present is decreased
  4. D.the relative amount of carbondioxide present is increased
  5. E.the ratio of oxygen to nitrogen in the system is increased.
Show the answer and explanation

Answer: D (the relative amount of carbondioxide present is increased)

Explanation

C + O2 → CO2: oxygen is used up and replaced by the same volume of carbon dioxide, so the proportion of CO2 goes up.

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Question 23

Periodic Table

Indicate which of the following statements is not true as we move from left to right along the Periodic Table:

  1. A.atomic number of elements increases
  2. B.atomic mass of elements increases
  3. C.electropositive character of elements increases
  4. D.electronegative character of elements increases
  5. E.number of electrons in the outermost orbits of elements increases.
Show the answer and explanation

Answer: C (electropositive character of elements increases)

Explanation

Across a period elements become less metallic: electropositive character decreases while electronegativity increases.

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Question 24

Electrolysis

0.1 Faraday of electricity was passed through a solution of copper (II) sulphate. The maximum weight of copper deposited on the cathode would be (Cu = 64)

  1. A.64.0 g
  2. B.32.0 g
  3. C.16.0 g
  4. D.6.4 g
  5. E.3.2 g
Show the answer and explanation

Answer: E (3.2 g)

Explanation

Cu2+ + 2e− → Cu, so 2 F deposit 64 g. 0.1 F deposits 64 × 0.1/2 = 3.2 g.

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Question 25

Hydrogen, Oxygen and Oxides

Which one of these compounds will NOT give an oxygen gas on heating?

  1. A.Manganese dioxide
  2. B.Hydrogen peroxide
  3. C.Zinc nitrate
  4. D.Sodium nitrate
  5. E.Ammonium nitrate.
Show the answer and explanation

Answer: E (Ammonium nitrate.)

Explanation

Ammonium nitrate decomposes to dinitrogen oxide and water (NH4NO3 → N2O + 2H2O), with no oxygen gas. The nitrates of zinc and sodium and hydrogen peroxide all release oxygen.

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Question 26

Metals and their Compounds

In the extraction of aluminium from purified bauxite by electrolysis, cryolite is used because

  1. A.it makes bauxite a better conductor of electricity
  2. B.it makes bauxite melt at a lower temperature
  3. C.it makes aluminium purer
  4. D.it prevents aluminium from getting oxidized
  5. E.it protects the carbon electrodes used in the process.
Show the answer and explanation

Answer: B (it makes bauxite melt at a lower temperature)

Explanation

Pure alumina melts above 2000°C. Dissolving it in molten cryolite lets the electrolysis run at about 950°C, saving a lot of energy.

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Question 27

Redox Reactions

In the redox reaction 2Fe2+ + Cl2 → 2Fe3+ + 2Cl−

  1. A.Cl2 is reduced because it has lost electrons
  2. B.Cl2 is reduced because its oxidation number has decreased
  3. C.Cl2 is reduced because its molecule is changed to two ions
  4. D.Fe2+ is reduced because it has lost electrons
  5. E.Fe2+ is reduced because it has gained electrons.
Show the answer and explanation

Answer: B (Cl2 is reduced because its oxidation number has decreased)

Explanation

Chlorine's oxidation number falls from 0 to −1 as it gains electrons, which is reduction. Fe2+ loses electrons and is oxidised.

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Question 28

Acids, Bases and Salts

An anhydride is

  1. A.a compound which has no water of crystallization
  2. B.an oxide whose solution in water has a pH greater than 7
  3. C.an oxide whose solution in water has a pH less than 7
  4. D.an oxide that has hydrogen atoms
  5. E.an amphoteric oxide.
Show the answer and explanation

Answer: C (an oxide whose solution in water has a pH less than 7)

Explanation

An (acid) anhydride is a non-metal oxide that reacts with water to form an acid, e.g. SO3 + H2O → H2SO4, so its solution has pH below 7.

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Question 29

Redox Reactions

In which of the following reactions is sulphur dioxide acting as an oxidizing agent?

  1. A.SO2 + 2HNO3 → H2SO4 + NO2 + Heat
  2. B.2SO2 + 2H2O + O2 → 2H2SO4.
  3. C.SO2 + 2H2O + Cl2 → H2SO4 + 2HCl.
  4. D.SO2 + 2H2S → 3S + 2H2O.
  5. E.SO2 + H2O → H2SO3.
Show the answer and explanation

Answer: D (SO2 + 2H2S → 3S + 2H2O.)

Explanation

In D the sulphur in SO2 goes from +4 to 0 (it is reduced), oxidising H2S to sulphur. In A, B and C SO2 is itself oxidised to H2SO4.

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Question 30

Nitrogen and its Compounds

Calcium hydroxide and ammonium chloride when heated together will give an important product. This compound may be obtained dry by

  1. A.dissolving it in water, recrystallizing it, and then drying in the oven
  2. B.passing it through a concentrated aqueous solution of sodium hydroxide
  3. C.passing it through concentrated sulphuric acid
  4. D.passing it through calcium oxide
  5. E.passing it through anhydrous calcium chloride.
Show the answer and explanation

Answer: D (passing it through calcium oxide)

Explanation

The product is ammonia, which is basic. It reacts with sulphuric acid and with calcium chloride, so it is dried with quicklime (calcium oxide).

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Question 31

Carbohydrates, Proteins and Amines

Starch can be converted to ethyl alcohol by

  1. A.distillation
  2. B.fermentation
  3. C.isomerization
  4. D.cracking
  5. E.cooking.
Show the answer and explanation

Answer: B (fermentation)

Explanation

Enzymes from malt and yeast break starch down to sugars and then ferment the sugars to ethanol and carbon dioxide.

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Question 32

Chemical Equilibrium

The reaction between hydrogen and iodine may be represented by the equation H2(g) + I2(g) ⇌ 2HI(g), and is exothermic. Therefore

  1. A.an increase in temperature favours the forward reaction
  2. B.an increase in pressure favours the backward reaction
  3. C.both pressure and temperature must be increased to favour the forward reaction
  4. D.a decrease in temperature will favour the forward reaction
  5. E.a decrease in pressure and an increase in temperature will favour the forward reaction.
Show the answer and explanation

Answer: D (a decrease in temperature will favour the forward reaction)

Explanation

For an exothermic forward reaction, lowering the temperature shifts the equilibrium to the right. Pressure has no effect because there are 2 moles of gas on each side.

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Question 33

Water

Weighed salts Y and Z were left exposed in the laboratory overnight. In the morning Y had gained weight, and Z had become liquid. What conclusion could be drawn about the nature of the two salts?

  1. A.Z is efflorescent
  2. B.Y and Z are efflorescent
  3. C.Y and Z are deliquescent
  4. D.Y and Z are hygroscopic
  5. E.Y is deliquescent.
Show the answer and explanation

Answer: D (Y and Z are hygroscopic)

Explanation

Both salts absorbed water from the air, so both are hygroscopic. Z absorbed so much that it dissolved (deliquescent), but Y only gained weight, so we cannot say Y is deliquescent.

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Question 34

Metals and their Compounds

In the manufacture of iron in the blast furnace, iron (III) oxide is mixed with coke and limestone, and different reactions occur in the process. Which of the following statements is true with respect to these reactions?

  1. A.The coke is a powerful reducing agent and easily converts the iron oxide to iron.
  2. B.The calcium carbonate reacts with SiO2, an earthly impurity in the ore, to form calcium silicate
  3. C.The coke will react with the iron produced to form steel
  4. D.All the carbondioxide required in the process comes from the decomposition of the calcium carbonate
  5. E.The calcium carbonate decomposes to give calcium oxide, which then forms calcium silicate with the earthly impurity.
Show the answer and explanation

Answer: E (The calcium carbonate decomposes to give calcium oxide, which then forms calcium silicate with the earthly impurity.)

Explanation

Limestone first decomposes to CaO and CO2; the CaO then combines with silica to form calcium silicate slag. The main reducing agent is carbon monoxide, not coke itself.

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Question 35

Gas Laws

Which of the following statements is true?

  1. A.An increase in the temperature of a given mass of gas increases the number of gas molecules.
  2. B.An increase in the temperature of the gas does not affect the kinetic energy
  3. C.An increase in the pressure of the gas is proportional to the increase in volume
  4. D.A decrease in the pressure of the gas is proportional to the increase in volume at constant temperature
  5. E.A decrease in the pressure of the gas decreases the number of gas molecules present.
Show the answer and explanation

Answer: D (A decrease in the pressure of the gas is proportional to the increase in volume at constant temperature)

Explanation

By Boyle's law, at constant temperature pressure falls as volume rises (PV = constant). The other statements are false: heating raises kinetic energy, and the number of molecules is fixed for a given mass.

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Question 36

Gas Laws

The vapour density of a gas may be defined as

  1. A.the mass of a unit volume of the gas compared to an equal volume of water vapour
  2. B.the mass of a unit volume of the gas compared to an equal volume of hydrogen
  3. C.the mass of a unit volume of the gas compared to an equal volume of oxygen
  4. D.the mass of a unit volume of the gas minus the vapour pressure of water
  5. E.two times the relative molecular mass of the gas.
Show the answer and explanation

Answer: B (the mass of a unit volume of the gas compared to an equal volume of hydrogen)

Explanation

Vapour density compares the mass of a volume of gas with the mass of the same volume of hydrogen under the same conditions; it equals half the relative molecular mass.

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Question 37

Energy Changes

The reaction 3C(s) + 2Fe2O3(s) = 4Fe(s) + 3CO2(g); ΔH = 46.0 kJ is

  1. A.adiabatic
  2. B.isobaric
  3. C.endothermic
  4. D.exothermic
  5. E.isothermal
Show the answer and explanation

Answer: C (endothermic)

Explanation

ΔH is positive (+46.0 kJ), so the reaction absorbs heat: it is endothermic.

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Question 38

Qualitative Analysis

The solution of a sample in a tube will be identified as a chloride if it gives

  1. A.a white precipitate on addition of AgNO3, and barium chloride solutions
  2. B.a white precipitate when acidified with HCl, and then AgNO3 solution added
  3. C.a white precipitate when acidified with dilute HNO3 and then AgNO3 solution added.
  4. D.a white precipitate when acidified with dilute H2SO4 and then barium nitrate solution added
  5. E.a pungent smell of chlorine gas when dilute HCl and MnO2 are added.
Show the answer and explanation

Answer: C (a white precipitate when acidified with dilute HNO3 and then AgNO3 solution added.)

Explanation

Silver nitrate gives white AgCl with chloride ions; acidifying with dilute nitric acid first removes carbonate and other ions that could also precipitate. Adding HCl would itself add chloride.

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Question 39

Hydrocarbons

Hydrogenation may be effected by

  1. A.the removal of hydrogen from an alkane in the presence of a catalyst
  2. B.the addition of hydrogen to an alkane in the presence of a catalyst
  3. C.the addition of hydrogen to an alkyne
  4. D.the removal of hydrogen from an alkyne
  5. E.the addition of hydrogen to an ethyl alcohol.
Show the answer and explanation

Answer: C (the addition of hydrogen to an alkyne)

Explanation

Hydrogenation is adding hydrogen to an unsaturated compound such as an alkyne or alkene. Alkanes are saturated and cannot take up more hydrogen.

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Question 40

Water

Two metallic ions associated with hard water are

  1. A.copper and zinc
  2. B.magnesium and silver
  3. C.calcium and magnesium
  4. D.potassium and tin
  5. E.sodium and lead.
Show the answer and explanation

Answer: C (calcium and magnesium)

Explanation

Water hardness is caused by dissolved calcium and magnesium ions, which form scum with soap.

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Question 41

Metals and their Compounds

Bronze is an alloy of

  1. A.copper, zinc and nickel
  2. B.aluminium and copper
  3. C.copper and zinc
  4. D.tin and zinc
  5. E.tin and copper.
Show the answer and explanation

Answer: E (tin and copper.)

Explanation

Bronze is mainly copper with tin. Copper with zinc is brass.

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Question 42

Mole Concept and Stoichiometry

Phosphorus burns in oxygen according to the equation P4 + 5O2 → P4O10. How many litres of oxygen will be required at S.T.P for complete oxidation of 12.4g of phosphorus? (P = 31, O = 16 and molar volume of a gas at S.T.P. = 22.4 litres).

  1. A.5.20
  2. B.11.20
  3. C.2.24
  4. D.20.20
  5. E.6.20
Show the answer and explanation

Answer: B (11.20)

Explanation

P4 = 124 g/mol, so 12.4 g = 0.1 mol. It needs 5 × 0.1 = 0.5 mol O2 = 0.5 × 22.4 = 11.2 litres.

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Question 43

Sulphur and its Compounds

On oxidizing anhydrous iron (II) sulphate, in addition to producing iron (III) oxide, which of the following is produced?

  1. A.SO2(g) + FeS(s)
  2. B.SO3(g) + FeS(s).
  3. C.SO2(g) + SO3(g)
  4. D.SO2(g) + H2S(g)
  5. E.SO3(g) + H2S(g).
Show the answer and explanation

Answer: C (SO2(g) + SO3(g))

Explanation

Strong heating of anhydrous iron(II) sulphate gives 2FeSO4 → Fe2O3 + SO2 + SO3.

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Question 44

Separation of Mixtures

One of the following techniques can be used to show that chlorophyll pigment is a mixture of chemical compounds and not a single coloured compound

  1. A.Cystallization
  2. B.Hydrolysis
  3. C.Sublimation
  4. D.Filtration
  5. E.Chromatography.
Show the answer and explanation

Answer: E (Chromatography.)

Explanation

Chromatography separates the coloured components of a mixture into separate spots or bands, showing chlorophyll extract contains several pigments.

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Question 45

Gas Laws

A gas occupies 30.0 dm3 at S.T.P. What volume would it occupy at 91°C and 380 mm Hg?

  1. A.20.0dm3
  2. B.40.0dm3
  3. C.60.0dm3
  4. D.80.0dm3
  5. E.100.0dm3
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Answer: D (80.0dm3)

Explanation

V2 = V1 × (P1/P2) × (T2/T1) = 30 × (760/380) × (364/273) = 30 × 2 × 1.33 = 80 dm3.

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Question 46

Alkanols

When excess ethanol is heated to 145°C in the presence of concentrated sulphuric acid, the product is

  1. A.diethyl ether
  2. B.ethyne
  3. C.diethyl sulphate
  4. D.acetone
  5. E.ethanoic acid
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Answer: A (diethyl ether)

Explanation

With excess ethanol at about 140–145°C, two ethanol molecules lose one water molecule to form diethyl ether (ethoxyethane). At higher temperatures (about 170°C) ethene forms instead.

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Question 47

Metals and their Compounds

Which of the following raw materials would be required for the smelting of iron ore in a blast furnace?

  1. A.CaCO3
  2. B.Zn(NO3)2
  3. C.CuSO4
  4. D.AlCl3
  5. E.CaSO4
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Answer: A (CaCO3)

Explanation

Limestone (CaCO3) is charged into the blast furnace with the ore and coke; it removes silica impurities as slag.

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Question 48

Qualitative Analysis

A piece of metal (M) is dissolved in nitric acid and the resulting solution is treated with a small quantity of sodium hydroxide to produce a white precipitate (B) which redissolves on the addition of excess alkali. The precipitate (B) when ignited in a crucible produces the oxide of the metal (M). The metal M is

  1. A.Zn
  2. B.Cu
  3. C.Al
  4. D.Au
  5. E.Ca
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Answer: A (Zn)

Explanation

Zinc dissolves in nitric acid, and its white hydroxide dissolves in excess NaOH (it is amphoteric). Copper gives a blue precipitate and calcium's does not redissolve; aluminium is made passive by nitric acid.

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