HomeClassroomJAMB Chemistry Past Questions & Answers JAMB Chemistry Past Questions & Answers By Classgist June 5, 2025 Classroom 0 Comments JAMB Chemistry Past Questions & Answers 1 / 40 1. Three solutions contain carbonate, sulphate and sulphide ions respectively. One test that will identify just ONE of them completely is by addition to each of them of A. barium chloride solution B. dilute hydrochloric acid C. lead nitrate solution D. calcium chloride solution E. sodium hydroxide solution Correct Answer: Option C Explanation You are given three solutions containing: Carbonate ions (CO₃²⁻) Sulphate ions (SO₄²⁻) Sulphide ions (S²⁻) When you add dilute hydrochloric acid (HCl): Carbonate ions react and release carbon dioxide (CO₂) gas, which causes effervescence (fizzing). → CO₃²⁻ + 2H⁺ → CO₂(g) + H₂O Sulphide ions also react to release hydrogen sulphide (H₂S) gas, which has a rotten egg smell. → S²⁻ + 2H⁺ → H₂S(g) Sulphate ions do not react with dilute HCl — no gas, no visible change. However, only carbonate produces a clear, visible reaction (effervescence) without requiring further testing. This makes dilute hydrochloric acid the best test to identify carbonate completely and reliably. ✅ Correct Answer: B. dilute hydrochloric acid 2 / 40 2. If excess zinc is added to a bluish green solution of copper (II) sulphate, and the excess zinc filtered off after completion of reaction, a colourless solution is obtained because A. both zinc and copper are metals B. the sulphate radical and the zinc ion are divalent C. zinc is more electropositive than copper D. both zinc and copper form depositive ions in solution E. zinc is a reducing agent Correct Answer: Option C Explanation Zinc displaces copper from copper sulphate and generates zinc sulphate solution when added to CuSO44 solution because zinc is a more reactive metal that displaces less reactive metal from its solution. This implies Zinc is more electropositive than Copper. The colour change shows it. 3 / 40 3. Consider the following exothermic reaction 2SO2(g) + O2(g) ↔ 2SO3(g) If the temperature of the reaction is reduced from 800°C to 500°C, an no other change takes place, then A. The reaction rate increases B. The concentration of SO3 decreases C. The concentration of SO3 increases D. SO2 gas becomes unreactive C. The concentration of SO3 increases Correct Answer: C Explanation: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g) is exothermic, meaning it releases heat. According to Le Chatelier's Principle, if you lower the temperature, the equilibrium will shift to produce more heat — that is, it will move in the forward direction (towards the formation of SO₃) to oppose the change. So, when the temperature is reduced from 800°C to 500°C, the system favors the forward reaction, and the concentration of SO₃ increases. ✅ Correct answer: C. concentration of SO₃ increases 4 / 40 4. The most common type of chemical reaction which alkanes undergo is A. substitution B. addition C. condensation D. polymerisation E. double decomposition Correct Answer: Option A Explanation The normal boiling point of a liquid is the temperature at which the vapour pressure of the liquid becomes equal to the external atmospheric pressure (usually 1 atm). At this point, bubbles of vapor form throughout the liquid and rise to the surface. That is why the correct answer is A. 5 / 40 5. Which of the following compounds will form a solution if exposed to air? A. Na2CO3·10H2O B. NaNO3 C. CuSO4 D. CaCl2 E. Na2SO4·10H2O Correct Answer: Option D Explanation Calcium chloride is a deliquescent substance. It attracts water from the atmosphere and then forms a solution. 6 / 40 6. The normal boiling point of a liquid is defined as? A. the temperature at which its vapour pressure equals the atmospheric pressure B. the temperature at which bubbles begin to form C. the temperature at which the vapour pressure equals 1 temperature D. the temperature at which the rate of condensation of vapour equals the rate of vaporisation of the liquid E. the temperature at which the space above the liquid is saturated Correct Answer: Option A Explanation: The normal boiling point of a liquid is the temperature at which the vapour pressure of the liquid becomes equal to the external atmospheric pressure (usually 1 atm). At this point, bubbles of vapor form throughout the liquid and rise to the surface. That is why the correct answer is A. 7 / 40 7. Hypochlorous acid is used as a bleach because A. it is a strong acid B. it yields chlorine readily in pure water C. it is an oxidising agent D. it is a weak acid E. it is a reducing agent Correct Answer: Option C Explanation Hypochlorous acid (HOCl) is used as a bleach because it acts as an oxidising agent. This means it can release oxygen or remove electrons from other substances. When it oxidises coloured substances, it breaks them down and removes the colour, which is how bleaching works. So, the correct answer is C. it is an oxidising agent. 8 / 40 8. The nucleus of an atom contains A. protons only B. neurons only C. protons and electrons D. neutrons and electrons E. protons and neutrons Correct Answer: E Explanation: The center of an atom is called the nucleus. Inside the nucleus, there are protons (which have a positive charge) and neutrons (which have no charge). Electrons are not in the nucleus—they move around it. So, the nucleus contains protons and neutrons only. That's why the correct answer is E. protons and neutrons. 9 / 40 9. An example of an alcohol is A. CCl4 B. CH3COOH C. CHCl3 D. C2H6 E. CH3OH Correct Answer: E. CH₃OH Explanation: Alcohols are organic compounds that contain a hydroxyl group (−OH) attached to a carbon atom. CH₃OH (methanol) is the simplest alcohol and contains the −OH group, making it an alcohol. The other options do not contain the −OH group: CCl₄ is carbon tetrachloride, CH₃COOH is a carboxylic acid (ethanoic acid), CHCl₃ is chloroform, and C₂H₆ is ethane, a simple alkane. Therefore, the correct answer is E. CH₃OH. 10 / 40 10. When ammonia and hydrogen ion bond together to form ammonium ion, the bond formed is called A. ionic bond B. electrovalent bond C. covalent bond D. co-ordinate bond E. hydrogen bond Correct Answer: Option D Explanation When ammonia (NH₃) reacts with a hydrogen ion (H⁺), it forms the ammonium ion (NH₄⁺). In this process, the nitrogen atom in ammonia donates its lone pair of electrons to bond with the hydrogen ion, which has no electrons. Since both electrons in the bond come from the same atom (nitrogen), the bond formed is called a co-ordinate bond (or dative covalent bond). This is different from an ionic or covalent bond where electrons are transferred or shared equally. Therefore, the correct answer is D. co-ordinate bond. 11 / 40 11. Which of the following is not a member of the homologous series of the paraffins (alkanes)? A. C3H8< C. C7H16 D. C15H32 E. C24H48 Correct Answer: Option E Explanation: Methane: CH4 Ethane: C2H6 Propane: C3H8 Butane: C4H10 Pentane: C5H12 Hexane: C6H14 Heptane: C7H16 Octane: C8H18 The formula for alkanes is: CnH2n+2 12 / 40 12. Which of the following reactions does not take place in the smelting of iron in a blast furnace? A. CaCO3(s) → CaO(s) + CO2(g) B. C(s) + O2(g) → CO2(g) 3Fe(s) + 2O2(g) → FeO4(s) D. SiO2(s) + CaO(s) → CaSiO3(s) E. CO2(g) + C(s) → 2CO(g) Correct Answer: Option C Explanation This reaction 3Fe(s)+2O2(g)→FeO4(s) Fe(s)+2O2(g)→FeO4(s) does not take place during the smelting of iron in a blast furnace 13 / 40 13. Which of the following gases may not be dried with concentrated sulphuric acid? A. HCl B. N2 C. Cl2 D. SO2 E. NH3 Correct answer: E Explanation: Concentrated sulphuric acid (H₂SO₄) is commonly used as a drying agent because it removes moisture (water vapor) from gases. However, ammonia (NH₃) cannot be dried using concentrated sulphuric acid because: Ammonia reacts chemically with sulphuric acid to form ammonium sulphate (NH₄)₂SO₄, a salt. This means H₂SO₄ doesn’t just dry ammonia — it removes it from the gas stream by reacting with it, so it cannot serve as a drying agent for NH₃. Other gases: HCl, N₂, Cl₂, SO₂: These do not react with concentrated H₂SO₄ and can safely be dried using it. ✅ Correct answer: E. NH₃ 14 / 40 14. Brass and bronze are both metallic alloys. Which of the following constituents is common to both alloys? A. Tin B. Zinc C. Copper D. Lead E. Aluminium Correct answer: C Explanation: Both brass and bronze are metallic alloys, and they share copper as a common component. Brass = Copper + Zinc Bronze = Copper + Tin (and sometimes small amounts of other elements) So, the common metal in both is Copper. 15 / 40 15. If 30cm3 3 of oxygen diffuses through a porous pot in 7 seconds, how long will it take 60cm3 3 of chlorine to diffuse through the same pot, if the vapour densities of oxygen and chlorine are 16 and 36 respectively? A. 9.3 sec B. 14 sec C. 21 sec D. 28 sec E. 30.3 sec ✅ Correct Answer: Option C Explanation: According to Graham’s Law of Diffusion of Gases, The rate of diffusion of a gas is inversely proportional to the square root of its density. That means: tOtC=dOdC\frac{t_O}{t_C} = \sqrt{\frac{d_O}{d_C}}tCtO=dCdO Where: tO=7t_O = 7tO=7 seconds (time for oxygen) VO=30V_O = 30VO=30 cm³ (volume of oxygen) dO=16d_O = 16dO=16 (vapor density of oxygen) VC=60V_C = 60VC=60 cm³ (volume of chlorine) dC=36d_C = 36dC=36 (vapor density of chlorine) tC=?t_C = ?tC=? (time for chlorine) Now apply Graham’s law: tOtC=dOdC=1636=46=23\frac{t_O}{t_C} = \sqrt{\frac{d_O}{d_C}} = \sqrt{\frac{16}{36}} = \frac{4}{6} = \frac{2}{3}tCtO=dCdO=3616=64=32 7tC=23\frac{7}{t_C} = \frac{2}{3}tC7=32 Now solve for tCt_CtC: tC=7×32=212=10.5 secondst_C = \frac{7 \times 3}{2} = \frac{21}{2} = 10.5 \text{ seconds}tC=27×3=221=10.5 seconds But note:The volume of chlorine is twice that of oxygen, so it will take twice as long. tC=2×10.5=21 secondst_C = 2 \times 10.5 = 21 \text{ seconds}tC=2×10.5=21 seconds ✅ Final Answer: Option C (21 seconds) 16 / 40 16. The reaction between an organic acid and an alcohol in the presence of an acid catalyst is known as; A. saponification B. dehydration C. esterification D. hydrolysis E. hydration Correct Answer: Option C Explanation Esterification, a reaction in which a carboxylic acid and an alcohol, heated in the presence of a mineral acid catalyst, form an ester and water: 17 / 40 17. During the electrolysis of copper II sulphate between platinum electrodes, if litmus solution is added to the anode compartment, A. the litmus turns blue but no gas is evolved B. the litmus turns blue and oxygen is evolved C. the litmus turns blue and hydrogen is evolved D. the litmus turns red and oxygen is evolved E. the litmus turns red and then becomes colourless Correct Answer: Option D Explanation Cu++ is discharged preferentially at the cathode OH−− is discharged preferentially at the anode The presence of SO442−2− and H++ makes the medium acidic Which makes the litmus turns red and oxygen is evolved 18 / 40 18. A sample of hard water contains some calcium sulphate and calcium hydrogen carbonate. The total hardness may therefore be removed by A. boiling the water B. adding excess calcium hydroxide C. adding a calculated amount of calcium hydroxide D. adding sodium carbonate E. adding magnesium hydroxide Correct Answer: D Explanation Hard water has calcium salts that make it hard. There are two types: Temporary hardness from calcium hydrogen carbonate – can be removed by boiling. Permanent hardness from calcium sulfate – boiling does not remove it. Since the water in this question has both types, boiling alone won't work. Sodium carbonate (washing soda) removes both types of hardness. It reacts with the calcium and makes it form a solid (calcium carbonate) that can be removed. So, the best way to remove all the hardness is by adding sodium carbonate. ✅ Answer: D. adding sodium carbonate 19 / 40 19. Which of the following metals cannot replace hydrogen from water or steam? A. Sodium B. Magnesium C. Iron D. Calcium E. Copper Correct Answer: Option E Explanation Copper cannot replace hydrogen from water or steam because it is less reactive than hydrogen and therefore cannot displace it in a chemical reaction. Copper is located below hydrogen in the reactivity series, indicating that it is less reactive and cannot displace hydrogen. 20 / 40 20. When each of the nitrates of Potassium, Magnesium and iron is heated, A. all the nitrates decompose to their oxides B. the nitrate of magnesium gives the nitrite and oxygen C. the nitrates of magnesium and iron give the oxides D. the nitrate of iron gives the nitrite and oxygen E. the nitrate of the magnesium is not decomposed Correct Answer: Option C Explanation When potassium nitrate is heated, it forms potassium nitrite and oxygen because potassium is a Group 1 metal. However, magnesium nitrate and iron nitrate decompose completely when heated to form their respective metal oxides, along with nitrogen dioxide and oxygen gases. Therefore, the correct statement is that the nitrates of magnesium and iron give the oxides. 21 / 40 21. The pH of four solutions W, X, Y, Z are 4, 6, 8, 10 respectively, therefore A. none of these solutions is acidic B. the pH of Y is made more acidic by addition of distilled water C. Z is the most acidic solution D. W is the most acidic solution E. X is neutral Correct Answer: Option D Explanation W is the most acidic solution since 4 < 6 < 8 < 10. The lower the value on the pH scale, the more acidic a solution. 22 / 40 22. When large hydrocarbon molecules are heated at high temperature in the presence of a catalyst to give smaller molecules, the process is known as A. disintegration B. polymerization C. cracking D. degradation E. distillation Correct Answer: Option C Explanation The process described is called cracking. When large hydrocarbon molecules are heated to high temperatures, often in the presence of a catalyst, they break down into smaller, more useful molecules. This process is crucial in the petrochemical industry for converting heavy fractions of crude oil into lighter, more valuable products like gasoline and fuel oil. 23 / 40 23. When heat is absorbed during a chemical reaction, the reaction is said to be A. thermodynamic B. exothermic C. isothermal D. endothermic E. thermostatic Correct Answer: Option D Explanation: When sodium chloride (NaCl) dissolves in water, the process is generally exothermic — it releases a small amount of heat. When metallic sodium (Na) is added to water, it reacts violently and exothermically, releasing a lot of heat, hydrogen gas, and forming sodium hydroxide (NaOH). This is a chemical reaction, not just simple dissolution. 24 / 40 24. When air which contains the gases Oxygen, nitrogen, carbondioxide, water vapour and the rare gases, is passed through alkaline pyrogallol and then over quicklime, the only gases left are? A. nitrogen and carbondioxide B. the rare gases C. nitrogen and oxygen D. nitrogen and the rare gases E. nitrogen, carbondioxide and the rare gases Correct Answer: Option D Explanation - Alkaline solutions of pyrogallol absorb oxygen efficiently. - Quicklime have a strong chemical affinity to absorb water. - At room temperature, Calcium oxide (CaO) will spontaneously absorb carbon dioxide from the atmosphere. 25 / 40 25. The oxidation state of chlorine in potassium chlorate is? A. +1 B. +2 C. +3 D. +5 E. +7 Correct Answer: Option D Explanation - potassium chlorate --> KClO33 valencies of K = +1, O = -2. : (+1) + Cl + ( -2 X 3 atoms ) = 0 Cl + 1 - 6 = 0 Cl = 5 ∴ The oxidation state of chlorine in potassium chlorate is +5 26 / 40 26. Which of the following statements is NOT correct? A. The average kinetic energy of a gas is directly proportional to its temperature B. At constant temperature, the volume of a gas increases as the pressure increases C. The pressure of a gas is directly proportional to the density. D. The temperature of a gas is directly proportional to its volume Correct Answer: Option B Explanation: A. Correct — The average kinetic energy of gas particles increases as temperature increases. B. NOT correct — At constant temperature (Boyle’s Law), volume decreases as pressure increases, not the other way around. C. Correct — Pressure is directly proportional to density when temperature is constant. D. Correct — Temperature and volume are directly proportional at constant pressure (Charles’s Law). So, the statement that is NOT correct is Option B. 27 / 40 27. When sodium chloride and metallic sodium are each dissolved in water A. both processes are exothermic B. both processes are endothermic C. the dissolution of metallic sodium is endothermic D. the dissolution of metallic sodium is exothermic E. the dissolution of sodium chloride is explosive Correct Answer: Option D Explanation When small quantities of sodium metal is added to water, there is an exothermic reaction, and they react to form sodium hydroxide and hydrogen. 28 / 40 28. Zinc Oxide is a? A. Basic Oxide B. Acidic Oxide C. Amphoteric Oxide D. Neutral Oxide E. Reactive Oxide Correct Answer: Option C Explanation Zinc oxide is an amphoteric oxide. - It will dissolve in both acids and alkalis 29 / 40 29. The periodic classification of elements is an arrangement of the elements in order of their A. Atomic Weights B. Isotopic Weights C. Molecular Weights D. Atomic Numbers E. Atomic Masses Correct Answer: Option D Explanation Henry Moseley arranged the elements in the periodic table by their atomic number and this gave rise to the statement of the modern periodic law 30 / 40 30. In the reaction between sodium hydroxide and sulphuric acid solutions, what volume of 0.5 molar sodium hydroxide would exactly neutralise 10cm3 of 1.25 molar sulphuric acid? A. 5cm3 B. 10cm3 C. 20cm3 D. 25cm3 E. 50cm3 Correct Answer: Option E Explanation 2NaOH+H2SO4=Na2SO4+2H2O2NaOH+H2SO4=Na2SO4+2H2O V x 0.5M = 2(10 x 1.25) 0.5V = 2 x 12.5 0.5V = 25 V = 250.5250.5 = 50cm3 31 / 40 31. A small quantity of solid ammonium chloride (NH4Cl) was heated gently in a test tube, the solid gradually disappears to produce two gases. Later, a white cloudy deposit was observed on the cooler part of the test tube. The ammonium chloride is said to have undergone? A. distillation B. sublimation C. precipitation D. evaporation E. decomposition Correct Answer: Option B Explanation Sublimation is the transition of a substance directly from the solid phase to the gas phase without passing through the intermediate liquid phase 32 / 40 32. Elements P, Q, R, S have 6, 11, 15, 17 electrons respectively, therefore, A. P will form an electrovalent bond with R B. Q will form a covalent bond with S C. R will form an electrovalent bond with S D. Q will form an electrovalent bond with S E. Q will form a covalent bond with R Correct Answer: Option D Explanation Element P with 6 electrons has an atomic number of 6 = 2, 4 → C Element Q with 11 electrons has an atomic number of 11 = 2, 8, 1 → Na Element R with 15 electrons has an atomic number of 15 = 2, 8, 5 → P Element S with 17 electrons has an atomic number of 17 = 2, 8, 7 → Cl Given the above is the electronic arrangement of P,Q,R,S elements, Q will form an electrovalent bond with S because element Q(metal) has a valence of electron of 1 it can donate to another element needing 1 electron, which is element S (a non-metal). Thus, electrovalent bond is formed in compounds where there is a transfer of electron from metals to non-metals. 33 / 40 33. An element X forms the following compounds with chlorine; XCl4, XCl3, XCl2. This illustrates the A. law of multiple proportions B. law of chemical proportions C. law of simple proportions D. law of conservation of mass E. law of definite proportions Correct Answer: Option A Explanation this question expresses the law of multiple proportions which states that if two elements A and B combine together to form more than one compound, the various masses of element B which combines with a fixed mass of B are in simple whole number ratios. e.g 34 / 40 34. You are provided with five gas jars containing SO2, CO2, H2, CO and NO respectively. Select a test from A to E which will identify ANY ONE of the gases completely A. pass each gas into lime water B. pass each gas into water and test with litmus paper C. pass each gas into concentrated sulphuric acid D. expose each gas to atmospheric air E. expose each gas to fumes of hydrogen chloride Correct Answer: A Explanation: Passing gases into lime water (calcium hydroxide solution) is a well-known test for carbon dioxide (CO₂). When CO₂ is bubbled through lime water, it reacts to form calcium carbonate, which makes the solution turn milky or cloudy. This is a specific and complete test for CO₂, meaning no other gas in the list gives the same result clearly. 35 / 40 35. A gas jar was inverted over burning yellow phosphorus floating over water in a beaker. After burning, the water level was found to rise in the gas jar. The water level rises because A. pressure inside the gas jar is greater than pressure outside it B. the air in the gas jar had been used up by burning C. oxygen in the gas jar had been used up by burning D. nitrogen in the gas jar had been used up by burning E. the temperature in the jar had risen considerably Correct Answer: C. Explanation: Yellow phosphorus reacts vigorously with oxygen when it burns, forming phosphorus pentoxide. This chemical reaction removes oxygen from the air inside the gas jar. Since oxygen is part of the air (about 21%), its removal causes a reduction in gas pressure inside the jar. As a result, water rises into the jar to fill the space left by the consumed oxygen. 36 / 40 36. In titration involving sodium hydroxide and dilute hydrochloric acid, where would you place the base? A. in the beaker B. in the conical flask C. in a burette D. in the standard flask E. in the measuring cylinder Correct Answer: Option B Explanation Add a few drops of indicator and put the conical flask on a white tile. Fill the burette with acid and note the starting volume. Slowly add the acid from the burette to the alkali in the conical flask, swirling to mix. 37 / 40 37. By means of filtration, one component can be obtained pure from an aqueous mixture of sodium chloride and? A. potassium nitrate B. sand C. lead nitrate D. sugar (glucose) E. starch Correct Answer: B Explanation: Filtration is a physical separation method used to separate an insoluble solid from a liquid. In this question, sodium chloride (common salt) is soluble in water—it dissolves completely. To use filtration, we need a second substance that does not dissolve in water. Among the options: Potassium nitrate, lead nitrate, and sugar (glucose) all dissolve in water, just like sodium chloride. So they cannot be separated from sodium chloride solution by filtration. Starch is only partially soluble and forms a colloidal suspension, not a clear mixture, making filtration less effective. Sand, however, is insoluble in water. It remains as a solid and does not dissolve. When the mixture is filtered, sand stays on the filter paper as a residue, and sodium chloride solution passes through. So, by using filtration, sand can be separated and obtained pure, making it the correct answer. ✅ Answer: Sand (Option B) 38 / 40 38. Which of the following changes is physical? A. Adding iron filing to aerated water B. Adding sodium metal to water C. Cooling a solution of Iron (II) sulphate to obtain the hydrated salt D. Cooling water to obtain ice E. Burning the domestic gas (Utilgas) for cooking Correct Answer: D Explanation:A physical change does not produce a new substance and is usually reversible. Cooling water to form ice is a change of state (liquid to solid) with no chemical reaction, making it a physical change. 39 / 40 39. Consider the following equation H2O + 2Fe2+ + Cl2 ↔ 2Fe3+ + 2Cl- + H2O. Which behaves as an oxidizing agent? A. Fe2+ B. Cl2 C. Fe3+ D. Cl− E. H2O Correct Answer: Option B Explanation - An oxidizing agent is a substance that causes oxidation by accepting electrons; therefore, it gets reduced. A reducing agent is a substance that causes reduction by losing electrons; therefore it gets oxidized. - Common examples of oxidizing agents include halogens (such as chlorine and fluorine) 40 / 40 40. Two gas cylinders contain ethylene (ethene) and acetylene respectively. One test which can be used to distinguish between them is by? A. passing each gas through bromine water B. passing each gas through dilute potassium permanganate solution C. passing each gas through silver nitrate solution D. treating each gas catalytically with excess hydrogen gas Correct Answer: Option C Explanation Acetylene reacts with ammoniacal AgNO3 solution to form a white precipitate of silver acetylide (AgC-=Cag) but ethylene does not Your score isThe average score is 19% 0% Restart quiz Related Posts 100 Likely Questions & Answers From Lekki Headmaster About Author Classgist Add a Comment Cancel replyYour email address will not be published. Required fields are marked *Comment:*Name:* Email Address:* Website: Save my name, email, and website in this browser for the next time I comment.
