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JAMB Chemistry 2022 past questions and answers

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

Question 4

Rates of Reaction

Na2S2O3(aq) + 2HCl(aq) → 2NaCl(aq) + H2O + SO2(g) + S(s)
In the above reaction, the greatest increase in the rate of the chemical reaction can be effected by

  1. A.a decrease in volume and an increase in pressure of the reactants
  2. B.an increase in temperature and a decrease in the concentration of the reactants
  3. C.an increase in temperature and an increase in the concentration of the reactants
  4. D.A decrease in temperature and an increase in the concentration of the reactants
Show the answer and explanation

Answer: C (an increase in temperature and an increase in the concentration of the reactants)

Explanation

The reactants are in solution, so pressure has no effect. Raising both temperature and concentration increases the number of effective collisions most.

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Question 5

Atomic Structure

The above diagram illustrates the electron sub-level for

Diagram for this question
  1. A.nitrogen
  2. B.carbon
  3. C.fluorine
  4. D.oxygen
Show the answer and explanation

Answer: D (oxygen)

Explanation

The boxes show 1s2 2s2 2p4, a total of 8 electrons, which is oxygen.

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Question 7

Water

The process whereby Na2CO3.10H2O loses its water of crystallization to the atmosphere is called

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

Answer: A (efflorescence)

Explanation

Efflorescence is the loss of water of crystallisation from a hydrated crystal when it is exposed to air.

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Question 9

Carbon and its Compounds

It is dangerous to inhale CO(g) mainly because it

  1. A.competes with oxygen in the blood
  2. B.can cause injury to the nervous system
  3. C.can cause lung cancer
  4. D.competes with CO2(g) in the blood
Show the answer and explanation

Answer: A (competes with oxygen in the blood)

Explanation

Carbon(II) oxide binds to haemoglobin far more strongly than oxygen, so the blood cannot carry enough oxygen.

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Question 13

Electrolysis

Calculate the number of moles of Cu(s) that will be deposited by 360 coulombs of electricity during the electrolysis of CuSO4(aq) using graphite electrodes.

  1. A.1.87×10−3 mole
  2. B.5.36×10−4 mole
  3. C.3.73×10−3 mole
  4. D.3.95×10−4 mole
Show the answer and explanation

Answer: A (1.87×10−3 mole)

Explanation

Cu2+ + 2e− → Cu, so 1 mole of Cu needs 2 × 96500 C. Moles = 360 ÷ 193000 = 1.87 × 10−3.

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Question 14

Nitrogen and its Compounds

A gas that has a pungent smell, turns red litmus paper blue and forms dense white fumes with hydrogen chloride is

  1. A.N2O
  2. B.N2
  3. C.NH3
  4. D.Cl2
Show the answer and explanation

Answer: C (NH3)

Explanation

Ammonia is the only common alkaline gas; it forms white fumes of NH4Cl with HCl.

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Question 17

Mole Concept and Stoichiometry

Calculate the percentage of sulphur in sulphur (iv) oxide [S=32, O = 16].

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

Answer: C (50%)

Explanation

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

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Question 23

Hydrocarbons

Which of the following flames is used by welders in the cutting of metals?

  1. A.acetylene flame
  2. B.butane gas flame
  3. C.oxy-acetylene flame
  4. D.kerosene flame
Show the answer and explanation

Answer: C (oxy-acetylene flame)

Explanation

Burning ethyne (acetylene) in pure oxygen gives a very hot flame used to cut and weld metals.

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Question 25

Chemical Equilibrium

aA + bB ⇌ cC + dD
In the above equation, the equilibrium constant is expressed as

  1. A.[A][B]/[C][D]
  2. B.[A]a[B]b/[C]c[D]d
  3. C.[C][D]/[A][B]
  4. D.[C]c[D]d/[A]a[B]b
Show the answer and explanation

Answer: D ([C]c[D]d/[A]a[B]b)

Explanation

K is products over reactants, each concentration raised to the power of its coefficient in the balanced equation.

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Question 26

Acids, Bases and Salts

The gas that cannot be dried with concentrated sulphuric acid is?

  1. A.NH3
  2. B.HCl
  3. C.SO2
  4. D.Cl2
Show the answer and explanation

Answer: A (NH3)

Explanation

Ammonia is basic, so it reacts with sulphuric acid to form ammonium sulphate instead of being dried.

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Question 27

Hydrocarbons

Which of the following will decolourized the purple colour of tetraoxomanganate (vii) ion?

  1. A.alkanols
  2. B.alkenes
  3. C.alkanes
  4. D.alkanals
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Answer: B (alkenes)

Explanation

Alkenes have a C=C double bond that is oxidised by acidified KMnO4, removing its purple colour.

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Question 28

Acids, Bases and Salts

What is the pH of an anhydride made from oxygen and non-metal when dissolved in water.

  1. A.pH > 7
  2. B.pH = 7
  3. C.it will not dissolve in water
  4. D.pH < 7
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Answer: D (pH < 7)

Explanation

Non-metal oxides such as SO2 and CO2 are acid anhydrides; they dissolve to form acids, so the pH is below 7.

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Question 29

Hydrocarbons

A type of chemical reaction that alkanes undergo is?

  1. A.addition
  2. B.substitution
  3. C.polymerization
  4. D.condensation
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Answer: B (substitution)

Explanation

Alkanes are saturated, so they react by substitution, e.g. a hydrogen atom replaced by chlorine in sunlight.

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Question 30

Redox Reactions

In the below redox equation H2O + 2Fe2+ + Cl2 ⇌ 2Fe3+ + 2Cl− + H2O which of the following behaves as an oxidising agent?

  1. A.Cl2
  2. B.Fe2+
  3. C.Cl−
  4. D.Fe3+
Show the answer and explanation

Answer: A (Cl2)

Explanation

Chlorine gains electrons (0 → −1), taking them from Fe2+, so Cl2 is the oxidising agent.

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Question 32

Hydrogen, Oxygen and Oxides

The only pair that contains two amphoteric oxides is?

  1. A.aluminium oxide, calcium oxide, zinc oxide
  2. B.sodium oxide, zinc oxide, magnesium oxide
  3. C.silver oxide, lead oxide, sodium oxide
  4. D.potassium oxide, lithium oxide, carbon dioxide
Show the answer and explanation

Answer: A (aluminium oxide, calcium oxide, zinc oxide)

Explanation

Aluminium oxide and zinc oxide are both amphoteric; each other set has at most one amphoteric oxide.

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Question 34

Air

In the above experiment Y is

Diagram for this question
  1. A.pure nitrogen
  2. B.a mixture of nitrogen and oxygen
  3. C.a mixture of nitrogen and carbon dioxide
  4. D.a mixture of nitrogen and inert gases
Show the answer and explanation

Answer: D (a mixture of nitrogen and inert gases)

Explanation

Alkaline pyrogallol absorbs oxygen (and carbon(IV) oxide) and CaCl2 absorbs water vapour, leaving nitrogen with the noble gases.

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Question 35

Electrolysis

Which of these is a strong electrolyte?

  1. A.ethyl acetate
  2. B.ethanol
  3. C.sodium formate
  4. D.glucose
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Answer: C (sodium formate)

Explanation

Sodium formate is an ionic salt that ionises fully in water; the others are covalent non-electrolytes.

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Question 36

Redox Reactions

Oxidation can be defined as

  1. A.loss of electrons
  2. B.gain of electrons
  3. C.loss of oxygen
  4. D.gain of hydrogen
Show the answer and explanation

Answer: A (loss of electrons)

Explanation

In electronic terms, oxidation is the loss of electrons (OIL RIG).

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Question 37

Gas Laws

An oxygen gas whose volume is 100cm3 at a pressure of 750mm Hg. Find the volume of the gas if the temperature is constant and the pressure is increased to 1000mmHg

  1. A.85cm3
  2. B.136.3cm3
  3. C.65cm3
  4. D.75cm3
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Answer: D (75cm3)

Explanation

Boyle's law: V2 = P1V1/P2 = 750 × 100/1000 = 75 cm3.

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Question 38

Carbohydrates, Proteins and Amines

Cotton consists almost pure.

  1. A.starch
  2. B.protein
  3. C.cellulose
  4. D.animal fibre
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Answer: C (cellulose)

Explanation

Cotton fibre is nearly pure cellulose, a polysaccharide.

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Question 39

Fats, Oils and Soaps

Alkanol obtained from the manufacture of soap is called

  1. A.ethanol
  2. B.glycol
  3. C.glycerol
  4. D.propanol
Show the answer and explanation

Answer: C (glycerol)

Explanation

Saponification of fats with alkali gives soap and glycerol (propane-1,2,3-triol).

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Question 40

Metals and their Compounds

Stainless steel consists of

  1. A.carbon, iron and lead
  2. B.carbon, iron and chromium
  3. C.carbon and iron only
  4. D.carbon, iron and copper
Show the answer and explanation

Answer: B (carbon, iron and chromium)

Explanation

Stainless steel is iron with carbon and chromium (often nickel too); chromium stops rusting.

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