Chemistry Past Questions | WAEC NECO, GCE, JAMB

Chemistry Past Questions | WAEC, NECO, GCE, JAMB. 100 Objectives and 100 theory past questions.

Chemistry is one of the most important and challenging subjects for students preparing for WAEC , NECO, GCE and JAMB exams in Nigeria. Success in these exams often depends on rigorous preparation, including studying past questions and answers. In this hall, we’ll show you the benefits of using past questions, provide chemistry past questions and answers for your WAEC/JAMB, and offer tips to excel.

Why You Should Study WAEC/JAMB Chemistry Past Questions and Answers?

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Chemistry Past Questions and Answers help you understand the format and structure of the exams. This includes the types of questions, marking scheme, and time allocation.
Focus on Frequently Tested Topics
Reviewing past questions highlights topics that examiners consistently prioritize, such as chemical bonding, stoichiometry, organic chemistry, and electrolysis.
Practice and Time Management
Attempting past questions under timed conditions improves your speed, accuracy, and confidence.

Self-Assessment
You can track your progress and identify weak areas to focus on before the actual exam.

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Chemistry Past Questions objs compiled 1 to 100

1. The bond formed when atoms share electrons is
A. Ionic
B. Metallic
C. Covalent
D. Electrovalent
Answer: C

2. Which of the following is a noble gas?
A. Oxygen
B. Chlorine
C. Argon
D. Nitrogen
Answer: C

3. Which of these is a chemical change?
A. Melting of ice
B. Dissolving salt in water
C. Burning of wood
D. Evaporation of alcohol
Answer: C

4. Which of the following has the highest electronegativity?
A. Fluorine
B. Oxygen
C. Nitrogen
D. Chlorine
Answer: A

5. Which separation technique is best for a mixture of sand and salt?
A. Distillation
B. Chromatography
C. Filtration
D. Evaporation
Answer: C

6. The number of protons in an atom is known as its
A. Atomic number
B. Mass number
C. Neutron number
D. Electron number
Answer: A

7. An atom with 17 protons and 18 electrons is
A. A cation
B. An anion
C. A molecule
D. Neutral
Answer: B

8. The pH of a neutral solution is
A. 0
B. 7
C. 14
D. 5
Answer: B

9. Which gas turns limewater milky?
A. Oxygen
B. Nitrogen
C. Carbon dioxide
D. Hydrogen
Answer: C

10. Which of the following metals can displace hydrogen from dilute acids?
A. Copper
B. Gold
C. Zinc
D. Silver
Answer: C

11. Which of the following is an alkali?
A. HCl
B. NaOH
C. H2SO4
D. CH3COOH
Answer: B

12. The chemical formula of calcium trioxocarbonate(IV) is
A. CaCO₃
B. Ca(CO₃)₂
C. Ca₂CO₃
D. Ca₂(CO₃)₂
Answer: A

13. Which of the following is not a compound?
A. Water
B. Oxygen
C. Sodium chloride
D. Carbon dioxide
Answer: B

14. An isotope of an element has
A. The same number of neutrons
B. A different number of protons
C. A different number of neutrons
D. A different atomic number
Answer: C

15. The main constituent of natural gas is
A. Methane
B. Propane
C. Butane
D. Ethane
Answer: A

16. The rate of a chemical reaction can be increased by
A. Decreasing temperature
B. Using a catalyst
C. Reducing surface area
D. Removing reactants
Answer: B

17. The periodic law states that
A. Elements are arranged by their atomic masses
B. Properties of elements are periodic functions of atomic number
C. Elements are grouped by physical properties
D. Atomic weights determine chemical behavior
Answer: B

18. The number of atoms in one mole of a substance is
A. 6.02 × 10²³
B. 3.01 × 10²³
C. 6.02 × 10²²
D. 3.01 × 10²²
Answer: A

19. A substance that speeds up a reaction but remains chemically unchanged is called
A. Reactant
B. Product
C. Catalyst
D. Enzyme
Answer: C

20. A basic oxide reacts with water to form
A. Acid
B. Salt
C. Base
D. Ester
Answer: C

21. Which of these is an exothermic reaction?
A. Photosynthesis
B. Melting
C. Combustion
D. Electrolysis
Answer: C

22. Which of the following is a salt?
A. NaCl
B. H₂O
C. NaOH
D. HCl
Answer: A

23. Which method is best for separating ink colors?
A. Distillation
B. Filtration
C. Chromatography
D. Crystallization
Answer: C

24. An example of a strong acid is
A. CH₃COOH
B. H₂CO₃
C. HCl
D. HNO₂
Answer: C

25. The atomic number of an element is equal to its
A. Number of neutrons
B. Mass number
C. Number of protons
D. Total electrons and neutrons
Answer: C

26. The most electronegative element is
A. Oxygen
B. Chlorine
C. Nitrogen
D. Fluorine
Answer: D

27. Which of these is an example of a covalent compound?
A. NaCl
B. MgCl₂
C. H₂O
D. KBr
Answer: C

28. The oxidation number of oxygen in H₂O is
A. 0
B. -1
C. -2
D. +2
Answer: C

29. A hydrocarbon with single bonds only is
A. Alkane
B. Alkene
C. Alkyne
D. Aromatic
Answer: A

30. Which of these is a reducing agent?
A. Cl₂
B. H₂
C. O₂
D. H₂O₂
Answer: B

31. Which gas is used in the manufacture of ammonia?
A. Carbon dioxide
B. Oxygen
C. Hydrogen
D. Helium
Answer: C

32. What is the IUPAC name for CH₄?
A. Methane
B. Methanol
C. Methanoic acid
D. Methyl
Answer: A

33. Electrolysis of acidified water produces
A. Hydrogen and oxygen
B. Hydrogen and chlorine
C. Oxygen and chlorine
D. Hydrogen and nitrogen
Answer: A

34. A catalyst used in the contact process is
A. Platinum
B. Vanadium(V) oxide
C. Manganese dioxide
D. Iron(III) oxide
Answer: B

35. Temporary hardness in water can be removed by
A. Boiling
B. Filtration
C. Sedimentation
D. Chlorination
Answer: A

36. The molar mass of Na₂CO₃ is
A. 106 g/mol
B. 60 g/mol
C. 100 g/mol
D. 96 g/mol
Answer: A

37. The pH of a strong acid is likely to be
A. 1
B. 5
C. 7
D. 9
Answer: A

38. The process of rusting involves
A. Hydrogenation
B. Oxidation
C. Reduction
D. Sublimation
Answer: B

39. The number of electrons in sodium is
A. 10
B. 11
C. 12
D. 13
Answer: B

40. Which of the following is a noble gas?
A. Helium
B. Hydrogen
C. Nitrogen
D. Oxygen
Answer: A

41. Which of these is a mixture?
A. Air
B. Water
C. Methane
D. Sodium chloride
Answer: A

42. Which of the following is not an allotrope of carbon?
A. Graphite
B. Diamond
C. Buckminsterfullerene
D. Carbon dioxide
Answer: D

43. The empirical formula of a compound shows
A. Actual number of atoms
B. Simplest ratio of atoms
C. Arrangement of atoms
D. Molecular mass
Answer: B

44. What is the color of litmus in an acid solution?
A. Blue
B. Yellow
C. Red
D. Green
Answer: C

45. Which of these metals is the most reactive?
A. Iron
B. Zinc
C. Sodium
D. Copper
Answer: C

46. What is the product of the neutralization of an acid and a base?
A. Salt and water
B. Salt and hydrogen
C. Base and water
D. Acid and gas
Answer: A

47. Which of these is a greenhouse gas?
A. Hydrogen
B. Carbon dioxide
C. Nitrogen
D. Helium
Answer: B

48. What is the valency of carbon?
A. 1
B. 2
C. 4
D. 3
Answer: C

49. The chemical used to test for the presence of water is
A. Cobalt(II) chloride
B. Sodium hydroxide
C. Litmus
D. Calcium oxide
Answer: A

50. Which of these does not sublimate?
A. Iodine
B. Ammonium chloride
C. Camphor
D. Sodium chloride
Answer: D

Section 2: Chemistry Past Questions: WAEC, NECO, GCE and JAMB objectives

Next section of 50 to 100 chemistry past questions from previous years

51. Which of these is a saturated hydrocarbon?
A. Ethene
B. Ethyne
C. Ethane
D. Benzene
Answer: C

52. What is the percentage composition of oxygen in H₂O?
A. 11.1%
B. 33.3%
C. 66.7%
D. 88.9%
Answer: D

53. Which of the following is used to remove permanent hardness of water?
A. Boiling
B. Sodium carbonate
C. Filtration
D. Distillation
Answer: B

54. The oxidation number of nitrogen in HNO₃ is
A. +1
B. +2
C. +3
D. +5
Answer: D

55. What type of reaction is CH₄ + 2O₂ → CO₂ + 2H₂O?
A. Substitution
B. Combustion
C. Addition
D. Neutralization
Answer: B

56. The device used to measure atmospheric pressure is
A. Thermometer
B. Barometer
C. Hydrometer
D. Anemometer
Answer: B

57. Which of these elements is a halogen?
A. Sulphur
B. Phosphorus
C. Iodine
D. Argon
Answer: C

58. The bleaching action of chlorine is due to the
A. Oxidizing property of chlorine
B. Formation of HCl
C. Basicity of chlorine
D. Reducing action of water
Answer: A

59. Which of these is a property of acids?
A. Turns red litmus blue
B. Feels slippery
C. Tastes sour
D. Turns blue litmus blue
Answer: C

60. Which of these is an endothermic process?
A. Freezing
B. Condensation
C. Evaporation
D. Combustion
Answer: C

61. What is the formula for calculating molar concentration?
A. Moles/Volume
B. Mass/Volume
C. Volume/Moles
D. Volume/Mass
Answer: A

62. What is the pH of a solution whose [H⁺] = 1 × 10⁻⁴ mol/dm³?
A. 4
B. 10
C. 7
D. 14
Answer: A

63. Which of the following is a chemical property of matter?
A. Melting point
B. Color
C. Reactivity
D. Density
Answer: C

64. Which gas is least soluble in water?
A. Carbon dioxide
B. Hydrogen
C. Ammonia
D. Sulphur dioxide
Answer: B

65. The IUPAC name of CH₃CH₂CH₃ is
A. Propene
B. Propane
C. Propyne
D. Butane
Answer: B

66. A solution which resists changes in pH when small amounts of acid or base are added is called
A. Indicator
B. Buffer
C. Neutralizer
D. Electrolyte
Answer: B

67. Which of the following gases would be released during the fermentation of sugar?
A. Oxygen
B. Carbon dioxide
C. Nitrogen
D. Hydrogen
Answer: B

68. The molecular formula of glucose is
A. C₆H₁₂O₆
B. C₆H₆O₆
C. C₅H₁₀O₅
D. C₂H₅OH
Answer: A

69. Which of these elements exhibits variable oxidation states?
A. Sodium
B. Neon
C. Iron
D. Magnesium
Answer: C

70. Which of these is the correct order of energy levels from lowest to highest?
A. s < p < d < f
B. f < d < p < s
C. p < s < d < f
D. d < s < p < f
Answer: A

71. Which gas is evolved when an acid reacts with a metal?
A. Carbon dioxide
B. Hydrogen
C. Oxygen
D. Chlorine
Answer: B

72. Electroplating involves
A. Heating metals
B. Freezing metals
C. Passing current through a solution
D. Mixing metals
Answer: C

73. Which of the following metals will not react with cold water?
A. Sodium
B. Potassium
C. Calcium
D. Copper
Answer: D

74. Which of these is a transition element?
A. Potassium
B. Iron
C. Calcium
D. Magnesium
Answer: B

75. The major constituent of air is
A. Oxygen
B. Nitrogen
C. Carbon dioxide
D. Hydrogen
Answer: B

76. The most reactive halogen is
A. Bromine
B. Chlorine
C. Fluorine
D. Iodine
Answer: C

77. An amphoteric oxide reacts with
A. Acids only
B. Bases only
C. Both acids and bases
D. Neither acids nor bases
Answer: C

78. Which of the following is not an acid-base indicator?
A. Methyl orange
B. Phenolphthalein
C. Litmus
D. Copper(II) sulphate
Answer: D

79. Which of the following is not an effect of acid rain?
A. Corrosion of metals
B. Damage to vegetation
C. Enrichment of soil
D. Pollution of water bodies
Answer: C

80. Which of the following is an example of a physical change?
A. Rusting of iron
B. Burning of wood
C. Melting of ice
D. Fermentation of glucose
Answer: C

81. Which of these elements has the smallest atomic radius?
A. Sodium
B. Fluorine
C. Chlorine
D. Oxygen
Answer: B

82. What is the oxidation state of sulphur in H₂SO₄?
A. +4
B. +6
C. +2
D. 0
Answer: B

83. What is the shape of the methane (CH₄) molecule?
A. Linear
B. Trigonal planar
C. Tetrahedral
D. Octahedral
Answer: C

84. Which of the following is not a greenhouse gas?
A. Methane
B. Carbon dioxide
C. Oxygen
D. Nitrous oxide
Answer: C

85. In the electrolysis of NaCl solution, the gas evolved at the anode is
A. Chlorine
B. Hydrogen
C. Oxygen
D. Nitrogen
Answer: A

86. Which of the following pollutants causes acid rain?
A. Carbon monoxide
B. Methane
C. Sulphur dioxide
D. Hydrocarbons
Answer: C

87. What type of bond is present in sodium chloride?
A. Covalent
B. Hydrogen
C. Ionic
D. Metallic
Answer: C

88. The number of neutrons in an atom of mass number 23 and atomic number 11 is
A. 11
B. 12
C. 23
D. 34
Answer: B

89. Which of the following gases is collected over water?
A. Hydrogen
B. Chlorine
C. Carbon dioxide
D. Ammonia
Answer: A

90. Which of the following does not affect the rate of reaction?
A. Pressure
B. Temperature
C. Mass number
D. Concentration
Answer: C

91. What is the name of CH₃COOH?
A. Methanoic acid
B. Ethanoic acid
C. Acetic acid
D. Butanoic acid
Answer: B

92. Which of the following is a weak acid?
A. HCl
B. H₂SO₄
C. HNO₃
D. CH₃COOH
Answer: D

93. What is the color of phenolphthalein in a basic solution?
A. Red
B. Pink
C. Colorless
D. Yellow
Answer: B

94. A compound with the empirical formula CH₂ has a molecular mass of 56. What is its molecular formula?
A. C₂H₄
B. C₃H₆
C. C₄H₈
D. C₅H₁₀
Answer: C

95. What is the atomic number of oxygen?
A. 6
B. 8
C. 10
D. 12
Answer: B

96. Which of these is not a property of bases?
A. They taste bitter
B. They are slippery
C. They turn blue litmus red
D. They have a pH above 7
Answer: C

97. Which process is used in the production of ethanol from glucose?
A. Combustion
B. Fermentation
C. Electrolysis
D. Oxidation
Answer: B

98. Which of the following is used as a drying agent?
A. NaCl
B. CaCl₂
C. KNO₃
D. HCl
Answer: B

99. Which separation method is used to purify crude oil?
A. Filtration
B. Distillation
C. Decantation
D. Chromatography
Answer: B

100. The atomicity of phosphorus is
A. 1
B. 2
C. 3
D. 4
Answer: D

Section 1. Chemistry Past Questions Theory

100 theories from past years chemistry past questions.

1. Define an acid according to Arrhenius’ theory.

Answer: According to Arrhenius’ theory, an acid is a substance that increases the concentration of hydrogen ions (H⁺) in an aqueous solution.

2. Name three types of chemical bonds.

Answer:

Ionic bond.
Covalent bond.

Metallic bond.

3. What is the oxidation number of sulfur in H₂SO₄?

Answer: The oxidation number of sulfur in H₂SO₄ is +6.

4. Calculate the molar mass of CaCO₃ (Calcium Carbonate).

Answer:

Ca = 40 g/mol, C = 12 g/mol, O = 16 g/mol × 3 = 48 g/mol.
Molar mass = 40 + 12 + 48 = 100 g/mol.

5. State the difference between endothermic and exothermic reactions.

Answer:

Endothermic reactions absorb heat from the surroundings.

Exothermic reactions release heat into the surroundings.

6. Write the formula of the following compounds:

(a) Sodium chloride
(b) Sulfuric acid
(c) Potassium nitrate
Answer:
(a) NaCl
(b) H₂SO₄
(c) KNO₃

7. What is the pH of a neutral solution at 25°C?

Answer: The pH of a neutral solution at 25°C is 7.

8. State two differences between crystalline and amorphous solids.

Answer:

Crystalline solids have a regular geometric pattern, while amorphous solids lack such a pattern.
Crystalline solids have a definite melting point, while amorphous solids do not.

9. What is the principle of the Haber process?

Answer: The Haber process involves the industrial production of ammonia (NH₃) by reacting nitrogen (N₂) and hydrogen (H₂) gases under high pressure, moderate temperature, and the use of an iron catalyst.

10. State two properties of metals.

Answer:

Good conductors of heat and electricity.
Malleable and ductile.

11. Define empirical formula.

Answer: The empirical formula is the simplest whole-number ratio of atoms of each element in a compound.

12. Determine the empirical formula of a compound with 40% carbon, 6.7% hydrogen, and 53.3% oxygen.

Answer:

Carbon: 40/12 = 3.33, Hydrogen: 6.7/1 = 6.7, Oxygen: 53.3/16 = 3.33.
Simplify: C = 1, H = 2, O = 1.
Empirical formula = CH₂O.

13. Name the gas evolved when a carbonate reacts with an acid.

Answer: Carbon dioxide (CO₂).

14. What is the valency of phosphorus in PCl₃?

Answer: The valency of phosphorus in PCl₃ is 3.

15. List three examples of alloys.

Answer:

Brass (copper and zinc).
Steel (iron and carbon).
Bronze (copper and tin).

16. State the Le Chatelier’s Principle.

Answer: Le Chatelier’s Principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change.

17. Calculate the concentration in mol/dm³ of 0.5 moles of NaOH in 250 cm³ solution.

Answer:
Concentration = Moles/Volume in dm³.
Volume = 250 cm³ = 0.25 dm³.
Concentration = 0.5/0.25 = 2 mol/dm³.

18. State two uses of sulfuric acid.

Answer:

Manufacture of fertilizers (e.g., ammonium sulfate).
Production of detergents and car batteries.

19. What is the main constituent of natural gas?

Answer: Methane (CH₄).

Section 2. Chemistry Past Questions | WAEC NECO, GCE, JAMB

20. Explain the term “electrolysis.”

Answer: Electrolysis is the process of decomposing a compound into its elements by passing an electric current through its molten or aqueous solution.

21. What is the difference between a homogeneous and a heterogeneous mixture?

Answer:

A homogeneous mixture has a uniform composition throughout (e.g., salt dissolved in water).
A heterogeneous mixture has a non-uniform composition with distinct components (e.g., oil and water).

22. What is the atomic number of chlorine?

Answer: The atomic number of chlorine is 17.

23. Define the term “mole” in chemistry.

Answer: A mole is the amount of substance that contains the same number of entities (atoms, molecules, ions, etc.) as there are in 12 grams of carbon-12, approximately 6.022×10236.022 \times 10^{23} entities.

24. What is the chemical formula for ammonia?

Answer: The chemical formula for ammonia is NH₃.

25. Name the process by which a liquid changes into a gas below its boiling point.

Answer: The process is called evaporation.

26. Write the balanced chemical equation for the reaction between hydrogen and oxygen to form water.

Answer:
2H₂(g) + O₂(g) → 2H₂O(l)

27. What is the term used to describe the maximum amount of solute that can dissolve in a solvent at a given temperature?

Answer: The term is solubility.

28. What is the difference between an electrolyte and a non-electrolyte?

Answer:

An electrolyte is a substance that conducts electricity when dissolved in water or molten (e.g., sodium chloride).
A non-electrolyte does not conduct electricity when dissolved in water (e.g., sugar).

29. Write the electronic configuration of chlorine (Cl).

Answer: The electronic configuration of chlorine (Cl) is 1s² 2s² 2p⁶ 3s² 3p⁵.

30. Define a salt and give two examples.

Answer: A salt is a compound formed by the neutralization of an acid with a base.
Examples:

Sodium chloride (NaCl)
Potassium nitrate (KNO₃)

31. What is a catalyst?

Answer: A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the reaction.

32. State the law of conservation of mass.

Answer: The law of conservation of mass states that mass cannot be created or destroyed in a chemical reaction; the total mass of reactants equals the total mass of products.

33. What is the molarity of a solution prepared by dissolving 2 moles of NaOH in 1 liter of water?

Answer:
Molarity = Moles of solute / Volume of solution in liters.
Molarity = 2 moles / 1 L = 2 M.

34. What is meant by the term “empirical formula”?

Answer: The empirical formula represents the simplest whole-number ratio of atoms of each element in a compound.

35. Name the three types of radioactive emissions.

Answer:

Alpha radiation (α)
Beta radiation (β)
Gamma radiation (γ)

36. State one use of hydrogen gas.

Answer: Hydrogen gas is used in the production of ammonia through the Haber process.

37. What is the name given to the process by which a liquid changes into a solid?

Answer: The process is called freezing.

38. What is the formula for calcium phosphate?

Answer: The formula for calcium phosphate is Ca₃(PO₄)₂.

39. What is the main difference between an ionic bond and a covalent bond?

Answer:

An ionic bond forms between a metal and a non-metal through the transfer of electrons.
A covalent bond forms between two non-metals through the sharing of electrons.

Section 3. Chemistry Past Questions | WAEC NECO, GCE, JAMB

40. What is an example of a neutralization reaction?

Answer: An example of a neutralization reaction is:
HCl + NaOH → NaCl + H₂O
(Here, hydrochloric acid reacts with sodium hydroxide to form salt and water.)

41. What is the process of dissolving sodium chloride in water?

Answer: The process involves the ionic bonds in sodium chloride being broken by the water molecules, which surround and separate the sodium and chloride ions, allowing them to disperse uniformly in the solution.

42. What is the difference between an alkali and a base?

Answer:

An alkali is a soluble base that dissolves in water to release hydroxide ions (OH⁻).
A base is a substance that can neutralize an acid but may or may not be soluble in water (e.g., sodium hydroxide, NaOH).

43. Define the term “stoichiometry” in chemistry.

Answer: Stoichiometry is the part of chemistry that involves the calculation of reactants and products in chemical reactions based on the laws of conservation of mass and moles.

44. What is the chemical equation for the reaction between zinc and hydrochloric acid?

Answer:
Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)

45. What is the primary use of sodium hydroxide in industry?

Answer: Sodium hydroxide (NaOH) is used in the manufacture of soaps and detergents, the production of paper, and as a strong base in various chemical processes.

46. What is the definition of an electrolyte?

Answer: An electrolyte is a substance that conducts electricity when dissolved in water or when molten due to the presence of free ions.

47. State the oxidation number of chlorine in NaCl.

Answer: In sodium chloride (NaCl), the oxidation number of chlorine is -1.

48. How does the presence of impurities affect the boiling point of a liquid?

Answer: The presence of impurities in a liquid raises its boiling point. This phenomenon is known as boiling point elevation.

49. What is the relationship between pressure and volume of a gas at constant temperature (Boyle’s Law)?

Answer: Boyle’s Law states that the pressure of a gas is inversely proportional to its volume at constant temperature. Mathematically, P∝1VP \propto \frac{1}{V}.

50. What is an isomer?

Answer: An isomer is a compound that has the same molecular formula as another compound but a different arrangement of atoms in space.

51. Explain the term “activation energy” in a chemical reaction.

Answer: Activation energy is the minimum energy required for a chemical reaction to occur. It is the energy needed to break bonds in the reactants.

52. What is the product of the reaction between sulfur dioxide (SO₂) and oxygen (O₂) in the presence of a catalyst?

Answer: The product of the reaction is sulfur trioxide (SO₃), which is formed in the contact process for sulfuric acid production:
2SO₂(g) + O₂(g) → 2SO₃(g)

53. What is the oxidation state of oxygen in hydrogen peroxide (H₂O₂)?

Answer: The oxidation state of oxygen in hydrogen peroxide (H₂O₂) is -1.

54. Define the term “redox reaction.”

Answer: A redox reaction is a chemical reaction in which there is a transfer of electrons between two species, involving both reduction (gain of electrons) and oxidation (loss of electrons).

55. What is the main use of nitrogen in the industry?

Answer: Nitrogen is primarily used in the production of ammonia for fertilizers through the Haber process, and it is also used to create inert atmospheres in industrial processes.

56. State the rule for determining the direction of electron flow in an electrochemical cell.

Answer: In an electrochemical cell, electrons flow from the anode (where oxidation occurs) to the cathode (where reduction occurs).

57. How does temperature affect the rate of a chemical reaction?

Answer: Increasing the temperature typically increases the rate of a chemical reaction by providing the reactants with more energy to collide more frequently and with higher energy.

58. What is the definition of a neutral substance in terms of pH?

Answer: A neutral substance has a pH of 7, indicating that the concentration of hydrogen ions (H⁺) is equal to the concentration of hydroxide ions (OH⁻).

59. Name the process used to separate a solid from a liquid by passing the mixture through a porous material.

Answer: The process is called filtration.

Section 4, Chemistry Past Questions | WAEC NECO, GCE, JAMB

60. What is the principle behind the use of fractional distillation?

Answer: Fractional distillation is based on the difference in boiling points of components in a mixture. It allows the separation of liquids with different boiling points by heating the mixture and collecting the vapor at different temperatures.

61. Define the term “enthalpy change.”

Answer: Enthalpy change refers to the heat absorbed or released during a chemical reaction at constant pressure.

62. What is the process by which an ionic solid dissolves in water?

Answer: When an ionic solid dissolves in water, the ions in the solid separate and disperse uniformly in the solvent due to the interactions between the water molecules and the ions.

63. What is the atomic number of oxygen?

Answer: The atomic number of oxygen is 8.

64. Write the equation for the reaction between methane (CH₄) and oxygen.

Answer:
CH₄ + 2O₂ → CO₂ + 2H₂O

65. What is the general formula for alkanes?

Answer: The general formula for alkanes is CₙH₂ₙ₊₂, where “n” represents the number of carbon atoms.

66. How is the concentration of a solution calculated?

Answer: The concentration of a solution is calculated by dividing the amount of solute (in moles) by the volume of the solution (in liters).

67. What is the product when zinc reacts with hydrochloric acid?

Answer: The product of the reaction between zinc and hydrochloric acid is zinc chloride (ZnCl₂) and hydrogen gas (H₂).

68. What is the difference between an alkali metal and an alkaline earth metal?

Answer:

Alkali metals are found in Group 1 of the periodic table and are highly reactive, especially with water.
Alkaline earth metals are in Group 2 and are less reactive than alkali metals.

69. Define the term “rate of reaction.”

Answer: The rate of reaction is the change in concentration of reactants or products per unit time.

70. What happens when chlorine gas is bubbled through a solution of sodium bromide?

Answer: Chlorine displaces bromine from sodium bromide because chlorine is more reactive, forming sodium chloride and bromine gas.

71. What is the meaning of “saturation” in a solution?

Answer: A solution is said to be saturated when no more solute can dissolve in it at a given temperature.

72. Name the process by which a liquid is converted into a gas.

Answer: The process is called evaporation when it occurs at temperatures below the boiling point and boiling when it occurs at the boiling point.

73. What is a halogen?

Answer: Halogens are elements found in Group 17 of the periodic table, including fluorine, chlorine, bromine, iodine, and astatine, which are highly reactive.

74. State the law of definite proportions.

Answer: The law of definite proportions states that a chemical compound always contains exactly the same proportion of elements by mass, regardless of the sample size.

75. What is the main use of chlorine in industry?

Answer: Chlorine is widely used in the production of disinfectants, plastics (such as PVC), and bleach.

76. What is the equation for the reaction between sulfuric acid and sodium hydroxide?

Answer:
H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O

77. How is the concentration of hydrogen ions in a solution related to its pH?

Answer: The pH of a solution is the negative logarithm of the hydrogen ion concentration. A lower pH indicates a higher concentration of hydrogen ions.

78. Define “sublimation” and give an example.

Answer: Sublimation is the process where a solid changes directly into a gas without passing through the liquid state. An example is the sublimation of iodine.

79. What is the difference between an exothermic reaction and an endothermic reaction?

Answer:

An exothermic reaction releases energy in the form of heat.
An endothermic reaction absorbs energy from the surroundings.

Section 5 Chemistry Past Questions | WAEC NECO, GCE, JAMB

80. What is the molar mass of sodium sulfate (Na₂SO₄)?

Answer:
Molar mass of Na₂SO₄ = 2(23) + 32 + 4(16) = 46 + 32 + 64 = 142 g/mol.

81. What is the pH of a neutral solution?

Answer: The pH of a neutral solution is 7, meaning the concentration of hydrogen ions equals the concentration of hydroxide ions.

82. What is the main component of natural gas?

Answer: The main component of natural gas is methane (CH₄).

83. How do you calculate the molar volume of a gas at standard temperature and pressure (STP)?

Answer: The molar volume of any ideal gas at STP is 22.4 L/mol.

84. What is the relationship between the pressure and volume of a gas at constant temperature (Boyle’s Law)?

Answer: Boyle’s Law states that the pressure of a gas is inversely proportional to its volume when the temperature is held constant. This means P∝1V

85. What is the oxidation state of sulfur in sulfuric acid (H₂SO₄)?

Answer: The oxidation state of sulfur in sulfuric acid (H₂SO₄) is +6.

86. What is a galvanic cell?

Answer: A galvanic cell is an electrochemical cell that generates electrical energy from spontaneous chemical reactions.

87. What is the purpose of adding a catalyst to a chemical reaction?

Answer: A catalyst is added to speed up the rate of a chemical reaction by lowering the activation energy, without being consumed in the reaction.

88. Write the chemical formula for calcium carbonate.

Answer: The chemical formula for calcium carbonate is CaCO₃.

89. What is the difference between an empirical formula and a molecular formula?

Answer:

The empirical formula represents the simplest whole-number ratio of elements in a compound.
The molecular formula shows the actual number of atoms of each element in a molecule of the compound.

90. What is the main use of sulfur dioxide (SO₂) in the industry?

Answer: Sulfur dioxide is primarily used in the production of sulfuric acid and as a preservative for dried fruits.

91. What is the general formula for the alkene family?

Answer: The general formula for alkenes is CₙH₂ₙ, where “n” represents the number of carbon atoms.

92. What is the name of the process where a solid turns into a gas without passing through the liquid phase?

Answer: The process is called sublimation.

93. What is the name given to a substance that can donate a proton (H⁺) in a chemical reaction?

Answer: A substance that can donate a proton is called an acid.

94. How is the density of a substance calculated?

Answer: Density is calculated by dividing the mass of the substance by its volume:
Density = Mass / Volume.

95. What is the relationship between the temperature and solubility of most solids in water?

Answer: For most solids, solubility increases as the temperature of the solvent increases.

96. What is the formula for calculating the energy absorbed or released during a phase change?

Answer: The formula is:
Energy = mass × latent heat of phase change.

97. Name the gas released when an acid reacts with a metal.

Answer: The gas released is hydrogen gas (H₂).

98. What type of bond is formed between sodium and chlorine to form sodium chloride (NaCl)?

Answer: Sodium chloride is formed by an ionic bond where electrons are transferred from sodium to chlorine.

99. What is the molar mass of methane (CH₄)?

Answer:
Molar mass of CH₄ = 12 + 4(1) = 16 g/mol.

100. What is the formula for the combustion of ethanol (C₂H₅OH)?

Answer:
The combustion of ethanol is:
C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O.

Chemistry Past Questions | WAEC NECO, GCE, JAMB

Conclusion on chemistry past questions

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Section 1. Chemistry Past Questions Theory

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