2022 JAMB Chemistry Past Questions and Answers

Questions

1. 1.

   In the extraction of iron, hot air is introduced into the blast furnace through?

   1. A.valves
   2. B.open-hearths
   3. C.arcs
   4. D.tuyeres

   Show answer

   Answer: D. tuyeres

   AI explanation

   Analysis of the Question

   The question asks for the specific component of a blast furnace used to inject hot air into the furnace during the extraction of iron from its ore (usually haematite, $Fe_2O_3$).

   Concept Explanation

   In the metallurgy of iron, a blast furnace is used to reduce iron ore into molten iron. The process requires a very high temperature, which is achieved by blowing a "blast" of hot air into the bottom of the furnace. This air reacts with coke (carbon) to produce heat and carbon(II) oxide, which acts as the reducing agent.

   The structure of a blast furnace includes specific openings near the base, known as tuyeres (pronounced twee-yairs). These are nozzles through which the preheated air is forced into the furnace at high pressure to ensure efficient combustion of the coke.

   Step-by-Step Solution

   1. Identify the process: The extraction of iron involves the blast furnace process.
   2. Understand the role of air: Hot air is essential for the combustion of coke to provide the heat and the reducing gas ($CO$) required for the reaction.
   3. Locate the entry point: The design of a blast furnace features specific ports or nozzles located around the lower part of the furnace stack.
   4. Evaluate the options: • Valves are used to control the flow of gases or liquids but are not the specific name for the furnace nozzles. • Open-hearths refer to a different type of furnace used in steelmaking, not the entry point for air in a blast furnace. • Arcs refer to electric arc furnaces, which use electricity rather than a blast of air for heating. • Tuyeres are the specific nozzles through which the hot blast of air enters the furnace.

   Conclusion

   Based on the design and operation of a blast furnace, the hot air is introduced through the tuyeres.

   Exam Tip: When studying metallurgy, always visualize the diagram of the blast furnace. Remember that "tuyeres" are the "nozzles" at the bottom—think of them as the "tuyere-tires" (nozzles) that keep the furnace breathing!

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2. 2.

   Alkanes are used mainly?

   1. A.in the textile industry
   2. B.in the hydrogenation of oils
   3. C.as domestic and industrial fuels
   4. D.as fine chemicals

   Show answer

   Answer: C. as domestic and industrial fuels

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3. 3.

   Electrons enter into orbitals in order of increasing energy as exemplified by?

   1. A.1S$^2$2S$^2$2PX$^2$2py$^2$2pz$^0$3s$^0$
   2. B.1S$^2$2S$^2$2PX$^2$2py$^1$2pz$^1$3s$^0$
   3. C.1S$^2$2S$^2$2PX$^1$2py$^1$2pz$^1$3s$^1$
   4. D.1S$^2$2S$^2$2PX$^2$2py$^2$2pz$^0$3s$^1$

   Show answer

   Answer: B. 1S$^2$2S$^2$2PX$^2$2py$^1$2pz$^1$3s$^0$

   AI explanation

   To solve this question, we need to apply two fundamental principles of electronic configuration:

   1. The Aufbau Principle

   This principle states that electrons fill orbitals in order of increasing energy, starting from the lowest energy level (1s) and moving upwards.

   2. Hund’s Rule of Maximum Multiplicity

   This rule states that for degenerate orbitals (orbitals with the same energy, like the three 2p orbitals: $2p_x, 2p_y, 2p_z$), electrons fill them singly first with parallel spins before pairing begins. This is because electrons are negatively charged and repel each other; they prefer to occupy separate orbitals if space is available.

   Step-by-Step Analysis

   The question asks for the configuration that correctly follows the order of increasing energy and the rules of orbital filling. Let's look at the total number of electrons in the options provided:

   • Option A: $2+2+2+2+0+0 = 8$ electrons. The $2p$ subshell has 4 electrons. According to Hund's Rule, these should be distributed as $2p_x^2, 2p_y^1, 2p_z^1$. Option A incorrectly pairs them all in $2p_x$ and $2p_y$ while leaving $2p_z$ empty.
   • Option B: $2+2+2+1+1+0 = 8$ electrons. This represents Oxygen (atomic number 8). The configuration $1s^2 2s^2 2p_x^2 2p_y^1 2p_z^1$ perfectly follows the Aufbau principle and Hund's Rule (the 4 electrons in the $2p$ subshell are distributed to minimize repulsion).
   • Option C: $2+2+1+1+1+1 = 8$ electrons. This is incorrect because it places an electron in the $3s$ orbital before the $2p$ subshell is fully filled.
   • Option D: $2+2+2+2+0+1 = 9$ electrons. This is an invalid configuration for an 8-electron system and violates the Aufbau principle by jumping to $3s$ before completing the $2p$ subshell.

   Conclusion

   Option B is the only one that correctly follows the Aufbau principle (filling lower energy levels first) and Hund's Rule (distributing electrons singly in degenerate orbitals before pairing).

   Exam Tip: When dealing with $p$-orbitals, always remember the "Bus Seat Rule": electrons act like people getting on a bus; they prefer to sit in an empty row before sitting next to someone else. Always fill the $p_x, p_y,$ and $p_z$ orbitals singly before adding a second electron to any of them.

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4. 4.

   2-methylprop-1-ene is a structural isomer of?

   1. A.But-1-yne
   2. B.2-methyl But-1-ene
   3. C.3-methyl prop-1-yne
   4. D.But-2-ene

   Show answer

   Answer: D. But-2-ene

   AI explanation

   Analysis

   To solve this, we need to determine the molecular formula of 2-methylprop-1-ene and compare it with the molecular formulas of the given options. Structural isomers are compounds that have the same molecular formula but different structural arrangements of atoms.

   Concept: Molecular Formula of Alkenes

   • 2-methylprop-1-ene is an alkene.
   • The general formula for acyclic alkenes (with one double bond) is $C_nH_{2n}$.
   • "Prop" indicates a chain of 3 carbons, and "methyl" adds 1 carbon, making a total of 4 carbons ($n=4$).
   • Therefore, the molecular formula is $C_4H_{2(4)} = \mathbf{C_4H_8}$.

   To be an isomer, the other compound must also have the molecular formula $C_4H_8$.

   Step-by-Step Solution

   1. Analyze 2-methylprop-1-ene: • Structure: $CH_2=C(CH_3)_2$ • Count: 4 Carbons, 8 Hydrogens ($C_4H_8$).

   2. Evaluate the Options: • A. But-1-yne: This is an alkyne (triple bond). General formula $C_nH_{2n-2}$. For $n=4$, it is $C_4H_6$. (Incorrect) • B. 2-methylbut-1-ene: This has 5 carbons (4 in the butane chain + 1 methyl group). Formula is $C_5H_{10}$. (Incorrect) • C. 3-methylprop-1-yne: This has 4 carbons but is an alkyne. Formula is $C_4H_6$. (Incorrect) • D. But-2-ene: This is an alkene with 4 carbons. Formula is $C_4H_8$. (Correct)

   Conclusion

   Since But-2-ene ($CH_3-CH=CH-CH_3$) has the same molecular formula ($C_4H_8$) as 2-methylprop-1-ene, they are structural isomers. Specifically, they are chain/positional isomers of each other.

   Exam Tip

   When asked for isomers, always count the number of carbon atoms first. If the number of carbons doesn't match, they cannot be isomers! If the carbon count matches, check the functional group (alkane, alkene, or alkyne) to ensure the hydrogen count matches the general formula.

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5. 5.

   How many neutrons are present in atom with mass number and atomic number 37 and 17 respectively?

   1. A.18
   2. B.20
   3. C.37
   4. D.17

   Show answer

   Answer: B. 20

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6. 6.

   H$^+$ + OH$^-$ → H$_2$O The equation above illustrates

   1. A.precipitation
   2. B.hydration
   3. C.hydrolysis
   4. D.neutralization

   Show answer

   Answer: D. neutralization

   AI explanation

   Analysis

   The question asks you to identify the chemical process represented by the ionic equation: H$^+$ + OH$^-$ → H$_2$O

   Concept Explanation

   This equation represents the fundamental reaction between an acid and a base.

   • H$^+$ ions are the characteristic ions provided by acids in an aqueous solution.
   • OH$^-$ ions are the characteristic ions provided by bases (alkalis) in an aqueous solution.
   • When these two ions combine, they form water (H$_2$O), which is a neutral molecule.

   This specific reaction is the core of a neutralization reaction, where an acid and a base react to form salt and water. Even when other spectator ions (like Na$^+$ or Cl$^-$) are present in the full chemical equation (e.g., HCl + NaOH → NaCl + H$_2$O), this ionic equation remains the same because it shows the actual chemical change occurring.

   Step-by-Step Solution

   1. Examine the reactants: We have a hydrogen ion (acidic) and a hydroxide ion (basic).
   2. Examine the product: The product is water, which has a pH of 7 (neutral).
   3. Evaluate the options: • Precipitation: Involves the formation of an insoluble solid from a solution. This is not happening here. • Hydration: Involves the addition of water to a substance. This is not the case here. • Hydrolysis: Involves the reaction of a substance with water to break it down. This is the reverse of this process. • Neutralization: This is the reaction between an acid and a base to produce salt and water. Since H$^+$ and OH$^-$ are the active components of acids and bases respectively, their combination is the definition of neutralization.

   Conclusion

   The reaction H$^+$ + OH$^-$ → H$_2$O is the net ionic equation for the neutralization of a strong acid by a strong base.

   Exam Tip

   Whenever you see a question involving H$^+$ and OH$^-$ reacting to form water, always look for "Neutralization" as your first choice. It is a classic JAMB question that tests your understanding of ionic equations!

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7. 7.

   SO$_2$ + O$_2$ → 2SO$_3$ In the reaction above, the most suitable catalyst is?

   1. A.chromium(vi)oxide
   2. B.iron(iii)oxide
   3. C.copper(i)oxide
   4. D.vanadium(v)oxide

   Show answer

   Answer: D. vanadium(v)oxide

   AI explanation

   1. Analyze the question

   The question asks for the most suitable catalyst used in the industrial production of sulfur(VI) oxide ($SO_3$) from sulfur(IV) oxide ($SO_2$) and oxygen ($O_2$). This specific reaction is a key stage in the Contact Process for the manufacture of sulfuric acid.

   2. Explain the concept

   In industrial chemistry, catalysts are substances that increase the rate of a chemical reaction without being consumed in the process. They work by providing an alternative reaction pathway with a lower activation energy.

   The reaction $2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$ is a reversible, exothermic reaction. To maximize the yield of $SO_3$ efficiently, the Contact Process employs a specific transition metal oxide catalyst to speed up the conversion.

   3. Show the solution

   • The Reaction: This is the catalytic oxidation of sulfur(IV) oxide.
   • The Catalyst: In the Contact Process, the mixture of $SO_2$ and $O_2$ is passed over a catalyst bed. Historically, platinum was used, but it is easily "poisoned" (rendered ineffective) by impurities like arsenic.
   • Modern Standard: Today, Vanadium(V) oxide ($V_2O_5$) is the standard catalyst used because it is cheaper, more resistant to poisoning, and highly effective at the required operating temperatures (about 450°C).

   Looking at the options provided:

   • A, B, and C are metal oxides, but they are not the standard industrial catalysts for this specific reaction.
   • D, Vanadium(V) oxide ($V_2O_5$), is the industry-standard catalyst for this reaction.

   4. Identify the answer

   The correct option is D.

   5. Tip

   When studying industrial processes for JAMB, always remember the "Catalyst-Process" pairs. For the Contact Process (Sulfuric Acid), remember V₂O₅. For the Haber Process (Ammonia), remember Finely divided Iron. These are classic JAMB favorites!

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8. 8.

   If the volume of a given mass of a gas at 0ºc is 29.5cm$^3$. What will be the volume of the gas at 15ºc, given that the pressure remains constant.

   1. A.31.6
   2. B.62.2
   3. C.32.7
   4. D.31.1

   Show answer

   Answer: D. 31.1

   AI explanation

   1. Analyze the question

   We are given the initial volume ($V_1$) and initial temperature ($T_1$) of a gas. We need to find the new volume ($V_2$) at a new temperature ($T_2$), while the pressure remains constant. This is a classic application of Charles's Law.

   2. Explain the concept

   Charles's Law states that for a fixed mass of gas at constant pressure, the volume is directly proportional to its absolute temperature (measured in Kelvin).

   The formula is:

   $\frac{V_1}{T_1} = \frac{V_2}{T_2}$

   Important Note: In gas law calculations, temperatures must always be converted from Celsius (°C) to Kelvin (K) by adding 273.15 (or simply 273 for most JAMB calculations).

   3. Show the solution

   Step 1: List the given values

   • $V_1 = 29.5 \text{ cm}^3$
   • $T_1 = 0^\circ\text{C} = 0 + 273 = 273 \text{ K}$
   • $T_2 = 15^\circ\text{C} = 15 + 273 = 288 \text{ K}$
   • $V_2 = ?$

   Step 2: Rearrange the formula to solve for $V_2$

   $V_2 = \frac{V_1 \times T_2}{T_1}$

   Step 3: Substitute the values into the equation

   $V_2 = \frac{29.5 \times 288}{273}$

   Step 4: Calculate the result

   $V_2 = \frac{8496}{273}$

   $V_2 \approx 31.12 \text{ cm}^3$

   Rounding to one decimal place, we get 31.1 cm³.

   4. Identify the answer

   Comparing our result to the given options, the correct choice is D.

   5. Tip

   Always remember the "Kelvin Rule": If you forget to convert Celsius to Kelvin in a gas law problem, you will almost certainly get the wrong answer. A quick way to check your work is to see if the volume changed in the same direction as the temperature—since the temperature increased, the volume must also increase.

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9. 9.

   Hard water is water with high concentrations of dissolved ions, in particular calcium and

   1. A.magnesium ions
   2. B.nitrogen ions
   3. C.phosporus ions
   4. D.helium ions

   Show answer

   Answer: A. magnesium ions

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10. 10.

    When heat is absorbed during a chemical reaction, the reaction is said to be

    1. A.thermodynamic
    2. B.exothermic
    3. C.isothermal
    4. D.endothermic

    Show answer

    Answer: D. endothermic

    AI explanation

    Analysis

    The question asks for the specific term used to describe a chemical reaction that absorbs heat from its surroundings.

    Concept Explanation

    In chemistry, reactions are classified based on their heat exchange with the environment:

    1. Exothermic Reactions: These reactions release heat energy into the surroundings. As a result, the temperature of the surroundings usually increases. The enthalpy change ($\Delta H$) for these reactions is negative.
    2. Endothermic Reactions: These reactions absorb heat energy from the surroundings. Because they "take in" heat, the surroundings lose energy and often feel cooler. The enthalpy change ($\Delta H$) for these reactions is positive.
    3. Isothermal: This refers to a process that occurs at a constant temperature, not necessarily one that absorbs heat.
    4. Thermodynamic: This is a broad branch of science dealing with heat, work, and energy, not a specific type of reaction classification.

    Step-by-Step Solution

    • Step 1: Identify the key phrase: "heat is absorbed."
    • Step 2: Recall the prefix meanings: "Exo-" means "out" (releasing heat), while "Endo-" means "in" (absorbing heat).
    • Step 3: Match the definition to the options. Since the reaction absorbs heat, it is classified as endothermic.

    Conclusion

    Exam Tip: To remember this easily, think of an "Endo"-skeleton (inside) vs. an "Exo"-skeleton (outside). An Endothermic reaction takes heat in, while an Exothermic reaction lets heat out.

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11. 11.

    Which of the following best represent solid gas mixture?

    1. A.milk
    2. B.kerosene
    3. C.soil
    4. D.smoke

    Show answer

    Answer: D. smoke

    AI explanation

    Analysis

    The question asks us to identify a mixture where a solid substance is dispersed within a gaseous medium (a solid-in-gas colloid).

    Concept Explanation

    In chemistry, mixtures where one substance is dispersed throughout another are called colloids. Colloids are classified based on the physical state of the dispersed phase (the substance being spread) and the dispersion medium (the substance it is spread into).

    • Solid-in-gas colloid: This occurs when solid particles are suspended in a gas. This is commonly referred to as an aerosol.
    • Let's evaluate the options: • Milk: This is an emulsion (liquid dispersed in liquid). • Kerosene: This is a liquid mixture (a solution of hydrocarbons). • Soil: This is a complex mixture of solid particles, water, and air, but it is primarily a solid-solid or solid-liquid mixture. • Smoke: This consists of fine solid particles (soot/ash) suspended in air (a gas).

    Step-by-Step Solution

    1. Identify the components: We are looking for a "solid" dispersed in a "gas."
    2. Evaluate Smoke: Smoke is produced by the incomplete combustion of fuels. The visible part of smoke is made up of tiny solid particles (carbon/soot) that are carried by the hot gases produced during combustion.
    3. Match with the definition: Since smoke is a collection of solid particles floating in a gas, it perfectly fits the definition of a solid-gas mixture (aerosol).
    4. Verify against other options: None of the other options represent a solid dispersed in a gas.

    Conclusion

    Exam Tip

    When dealing with colloid questions in JAMB, remember this simple table:

    • Smoke: Solid in Gas
    • Fog/Mist: Liquid in Gas
    • Milk/Mayonnaise: Liquid in Liquid (Emulsion)
    • Foam: Gas in Liquid

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12. 12.

    The reactions below represent neutralization reaction, in which of them is the value of ΔH highest?

    1. A.CH$_3$CH$_2$COOH + KOH → CH$_3$CH$_2$COOK + H$_2$O
    2. B.NH$_4$OH + HCL → NH$_4$ + H$_2$O
    3. C.NaOH + HCL → NaCL + H$_2$O
    4. D.CH$_3$COOH + NaOH → CH$_3$COONa + H$_2$O

    Show answer

    Answer: C. NaOH + HCL → NaCL + H$_2$O

    AI explanation

    1. Analyze the question

    The question asks you to identify which of the given neutralization reactions has the highest enthalpy of neutralization ($\Delta H$). In chemistry, the enthalpy of neutralization is the heat energy released when one mole of water is formed from the reaction of an acid and a base.

    2. Explain the concept

    The standard enthalpy of neutralization for a strong acid reacting with a strong base is a constant value of approximately -57.3 kJ/mol. This is because both the strong acid and the strong base dissociate completely into ions in water. The reaction is essentially just the combination of hydrogen ions ($H^+$) and hydroxide ions ($OH^-$) to form water:

    $H^+_{(aq)} + OH^-_{(aq)} \rightarrow H_2O_{(l)}$

    However, when a weak acid or a weak base is involved, some of the heat released is consumed to complete the dissociation of the weak electrolyte. Consequently, the net heat released is less than -57.3 kJ/mol.

    3. Show the solution

    Let's analyze the nature of the reactants in each option:

    • Option A: $CH_3CH_2COOH$ (Propanoic acid) is a weak acid, and $KOH$ is a strong base. The heat of neutralization will be less than -57.3 kJ/mol.
    • Option B: $NH_4OH$ (Ammonium hydroxide) is a weak base, and $HCl$ is a strong acid. The heat of neutralization will be less than -57.3 kJ/mol.
    • Option C: $NaOH$ is a strong base, and $HCl$ is a strong acid. This reaction involves the complete neutralization of strong species, resulting in the maximum standard enthalpy of approximately -57.3 kJ/mol.
    • Option D: $CH_3COOH$ (Ethanoic acid) is a weak acid, and $NaOH$ is a strong base. The heat of neutralization will be less than -57.3 kJ/mol.

    Comparing these, Option C represents the reaction between a strong acid and a strong base, which yields the highest amount of energy released (the highest absolute value of $\Delta H$).

    4. Identify the answer

    The correct option is C.

    5. Tip

    Always remember: Strong + Strong = Maximum Heat. If you see a weak acid or a weak base in the equation, the heat of neutralization will always be lower than the standard -57.3 kJ/mol because energy is "wasted" on breaking the bonds of the undissociated weak acid or base.

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13. 13.

    The pollutant usually presents in a city which generates its electricity from coal?

    1. A.fog
    2. B.carbon(ii)oxide
    3. C.smog
    4. D.sulphur(iv)oxide

    Show answer

    Answer: D. sulphur(iv)oxide

    AI explanation

    Analysis

    The question asks for the primary pollutant associated with cities that rely on coal-fired power plants for electricity generation. To answer this, we must look at the chemical composition of coal and the by-products of its combustion.

    Concept Explanation

    Coal is a fossil fuel composed primarily of carbon, but it also contains significant amounts of impurities, most notably sulfur.

    When coal is burned in power plants to generate electricity, the following chemical reaction occurs:

    $S(s) + O_2(g) \rightarrow SO_2(g)$

    The sulfur in the coal reacts with oxygen in the air to produce Sulphur(IV) oxide (also known as sulfur dioxide). This gas is a major air pollutant and is a primary contributor to acid rain and respiratory issues in urban areas. While coal combustion can also produce carbon(II) oxide (if combustion is incomplete), Sulphur(IV) oxide is the characteristic pollutant specifically linked to the sulfur content in coal.

    Step-by-Step Solution

    1. Identify the source: The question specifies "electricity from coal."
    2. Analyze the fuel: Coal contains carbon and sulfur impurities.
    3. Analyze the combustion process: • Complete combustion of carbon produces Carbon(IV) oxide ($CO_2$). • Incomplete combustion produces Carbon(II) oxide ($CO$). • Combustion of sulfur impurities produces Sulphur(IV) oxide ($SO_2$).
    4. Evaluate the options: • Fog (A): A natural weather phenomenon, not a pollutant. • Carbon(II) oxide (B): Produced by incomplete combustion of any carbon-based fuel (like petrol in cars), not specific to coal. • Smog (C): A mixture of pollutants; while coal can contribute to it, it is not the specific chemical pollutant emitted by the combustion process itself. • Sulphur(IV) oxide (D): The direct chemical product of burning the sulfur impurities found in coal.

    Conclusion

    Sulphur(IV) oxide is the most significant pollutant associated with coal combustion in power plants.

    Exam Tip: Whenever you see a question about "coal" or "fossil fuels" and "pollution," always look for options involving Sulfur or Acid Rain. These are classic JAMB keywords!

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14. 14.

    A chemical widely used as a fertilizer is?

    1. A.galena
    2. B.bauxite
    3. C.emerald
    4. D.nitrochalk

    Show answer

    Answer: D. nitrochalk

    AI explanation

    Analysis of the Question

    The question asks to identify a chemical compound from the given list that is commonly used as a fertilizer in agriculture.

    Concept Explanation

    Fertilizers are substances added to soil to provide essential nutrients (like Nitrogen, Phosphorus, and Potassium) to plants to improve their growth and yield.

    • Nitrogen-based fertilizers are particularly important for leafy growth.
    • Nitrochalk is a common commercial fertilizer. It is a mixture of ammonium nitrate ($NH_4NO_3$) and calcium carbonate ($CaCO_3$). The calcium carbonate is added to neutralize the acidity of the ammonium nitrate, making it safer for soil application.

    Let's look at the other options:

    • Galena ($PbS$): This is the primary ore of lead. It is not used as a fertilizer.
    • Bauxite ($Al_2O_3 \cdot 2H_2O$): This is the primary ore of aluminium. It is used in the production of aluminium metal, not as a fertilizer.
    • Emerald: This is a gemstone (a variety of the mineral beryl). It is used in jewelry and has no agricultural application as a fertilizer.

    Step-by-Step Solution

    1. Evaluate the options: We eliminate Galena (lead ore), Bauxite (aluminium ore), and Emerald (gemstone) because they are industrial minerals or precious stones, not agricultural nutrients.
    2. Analyze Nitrochalk: Nitrochalk provides nitrogen, which is a primary macronutrient for plants. It is specifically formulated for agricultural use to ensure the soil pH remains balanced while providing the necessary nitrogen.
    3. Conclusion: Among the choices provided, Nitrochalk is the only substance recognized as a chemical fertilizer.

    Exam Strategy Tip

    When you see questions about "common chemicals" in JAMB Chemistry, try to categorize them by their industrial use. If you see an option that sounds like a rock or an ore (like Bauxite or Galena), it is rarely a fertilizer. Look for compounds containing Nitrogen ($N$), Phosphorus ($P$), or Potassium ($K$), as these are the "big three" elements in fertilizers.

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15. 15.

    Wrought iron is obtained by heating cast iron in a furnace with?

    1. A.magnetite
    2. B.haematite
    3. C.carbon(ii)oxide
    4. D.calcium trioxosilicate(iv)

    Show answer

    Answer: B. haematite

    AI explanation

    Analysis of the Question

    The question asks for the substance used in a furnace to convert cast iron into wrought iron. This process is known as the "puddling process" or "reverberatory furnace process."

    Concept Explanation

    Cast iron contains a high percentage of carbon (about 2% to 4.5%) and other impurities like silicon, sulfur, and phosphorus, which make it brittle. To produce wrought iron (which is almost pure iron), these impurities must be removed through oxidation.

    When cast iron is heated in a reverberatory furnace, it is lined with haematite ($Fe_2O_3$). The haematite acts as an oxidizing agent. It reacts with the carbon and other impurities in the cast iron to oxidize them:

    • Carbon is oxidized to carbon(IV) oxide ($CO_2$), which escapes as a gas.
    • Silicon is oxidized to silicon(IV) oxide ($SiO_2$), which forms slag.

    Step-by-Step Solution

    1. Identify the goal: The goal is to reduce the carbon content of cast iron to produce wrought iron.
    2. Identify the process: The process involves heating cast iron in a furnace lined with an oxidizing agent.
    3. Evaluate the options: • Magnetite ($Fe_3O_4$): While it is an iron ore, it is not the standard lining used in the puddling furnace for this specific conversion. • Haematite ($Fe_2O_3$): This is the specific iron ore used to line the furnace. It provides the oxygen necessary to burn off the excess carbon and impurities. • Carbon(II) oxide ($CO$): This is a reducing agent, not an oxidizing agent. It would not help remove carbon from the iron. • Calcium trioxosilicate(iv) ($CaSiO_3$): This is a slag component, not the primary oxidizing agent used to line the furnace.
    4. Conclusion: The haematite ($Fe_2O_3$) reacts with the carbon in the molten cast iron: $Fe_2O_3 + 3C \rightarrow 2Fe + 3CO$

    Correct Answer

    The correct option is B.

    Exam Tip

    When studying metallurgy, always distinguish between reducing agents (like $CO$ used in the Blast Furnace to extract iron from ore) and oxidizing agents (like haematite used in the Puddling Furnace to purify iron). Remember: Blast Furnace = Reduction; Puddling Furnace = Oxidation.

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16. 16.

    An organic functional group which can likely decolorize ammoniacal silver nitrate is?

    1. A.alkene
    2. B.alkane
    3. C.alkyne
    4. D.alkanol

    Show answer

    Answer: C. alkyne

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17. 17.

    An organic compound which liberate carbon(iv)oxide from trioxocarbonate(iv) solution is likely to be?

    1. A.C$_2$H$_5$OH
    2. B.C$_3$H$_4$
    3. C.C$_6$H$_6$
    4. D.CH$_3$COOH

    Show answer

    Answer: D. CH$_3$COOH

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18. 18.

    The dehydration of CH$_3$CH$_2$CH$_2$CH$_2$OH will give?

    1. A.HC≡CCH$_2$CH$_3$
    2. B.CH$_2$≡CH$_2$CH$_3$
    3. C.CH$_3$C≡CCH$_3$
    4. D.CH$_3$CH=CHCH$_3$

    Show answer

    Answer: D. CH$_3$CH=CHCH$_3$

    AI explanation

    Analysis

    The question asks for the product formed when butan-1-ol ($\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{OH}$) undergoes dehydration. Dehydration is the removal of a water molecule ($\text{H}_2\text{O}$) from an alcohol to form an alkene.

    Concept Explanation

    Dehydration of alcohols typically occurs in the presence of an acid catalyst (like concentrated $\text{H}_2\text{SO}_4$) and heat. According to Zaitsev’s Rule, when an alcohol is dehydrated, the hydrogen atom is removed from the $\beta$-carbon (the carbon adjacent to the one holding the hydroxyl group) that has the fewest hydrogen atoms, leading to the formation of the most substituted alkene (the most stable product).

    Step-by-Step Solution

    1. Identify the structure: The reactant is butan-1-ol: $\text{CH}_3-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{OH}$.
    2. Identify the carbons: • The carbon attached to the $-\text{OH}$ group is the $\alpha$-carbon. • The carbon next to it ($\text{CH}_2$) is the $\beta$-carbon.
    3. Remove water: To form the alkene, we remove the $-\text{OH}$ group from the $\alpha$-carbon and one hydrogen atom from the $\beta$-carbon.
    4. Rearrangement: In the presence of strong acid, the carbocation formed can undergo a 1,2-hydride shift to form a more stable secondary carbocation. • Initial: $\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2^+$ (primary) • Rearranged: $\text{CH}_3\text{CH}_2\text{CH}^+\text{CH}_3$ (secondary)
    5. Formation of the double bond: The loss of a proton from the secondary carbocation results in the formation of but-2-ene ($\text{CH}_3\text{CH=CHCH}_3$).

    Evaluation of Options

    • A and C are alkynes (triple bonds), which are not produced by simple dehydration.
    • B represents but-1-ene ($\text{CH}_2\text{=CHCH}_2\text{CH}_3$), which is a minor product.
    • D represents but-2-ene ($\text{CH}_3\text{CH=CHCH}_3$), which is the major product due to its higher stability.

    Exam Tip

    When dealing with dehydration of alcohols with four or more carbons, always look for the "most substituted" alkene as your major product. Remember the mantra: "The rich get richer" (for Markovnikov's addition) and "The poor get poorer" (for Zaitsev's elimination).

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19. 19.

    The sub-atomic particles located in the nucleus of an atom are?

    1. A.neutron and proton
    2. B.proton and electron
    3. C.proton and ions
    4. D.neutron and electron

    Show answer

    Answer: A. neutron and proton

    AI explanation

    1. Analyze the question

    The question asks for the specific sub-atomic particles that are found within the nucleus (the central core) of an atom.

    2. Explain the concept

    An atom is composed of three main sub-atomic particles:

    • Protons: These are positively charged particles found inside the nucleus.
    • Neutrons: These are neutral (no charge) particles also found inside the nucleus.
    • Electrons: These are negatively charged particles that orbit the nucleus in specific energy levels or shells.

    The nucleus is the dense center of the atom, and because it contains both protons and neutrons, it is collectively referred to as the nucleon.

    3. Show the solution

    • Step 1: Identify the location of each particle. • Protons: Nucleus • Neutrons: Nucleus • Electrons: Shells/Orbitals outside the nucleus
    • Step 2: Evaluate the options based on the location. • Option A (neutron and proton): Both are in the nucleus. This is correct. • Option B (proton and electron): Electrons are not in the nucleus. • Option C (proton and ions): Ions are charged atoms, not sub-atomic particles found in the nucleus. • Option D (neutron and electron): Electrons are not in the nucleus.

    4. Identify the answer

    The correct option is A.

    5. Tip

    Remember the acronym "PEN":

    • Proton = Positive (in the nucleus)
    • Electron = External (outside the nucleus)
    • Neutron = Neutral (in the nucleus)

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20. 20.

    Addition of charcoal to the filter bed of sand during water treatment for township supply is to?

    1. A.prevent goiter
    2. B.prevent tooth decay
    3. C.remove odour
    4. D.kill germs

    Show answer

    Answer: C. remove odour

    AI explanation

    Analysis

    This question tests your knowledge of the water treatment process, specifically the function of different layers in a filtration bed. You are asked to identify the specific purpose of adding charcoal (activated carbon) to a sand filter.

    Concept: Water Treatment Processes

    In a municipal water treatment plant, water passes through several stages to make it safe for consumption:

    1. Sedimentation: Large particles settle at the bottom.
    2. Coagulation/Flocculation: Chemicals like alum are added to clump smaller particles together.
    3. Filtration: Water passes through layers of sand and gravel to remove remaining suspended solids.
    4. Activated Charcoal (Carbon) Treatment: This is often added to the filter bed or used as a separate stage. Activated charcoal has a highly porous structure with a very large surface area. It acts as an adsorbent, meaning it traps molecules on its surface.

    Step-by-Step Solution

    • Step 1: Analyze the options provided. • A (Prevent goiter): This is achieved by adding iodine to water or salt, not by charcoal. • B (Prevent tooth decay): This is achieved by adding fluoride to the water supply. • C (Remove odour): Charcoal is well-known for its ability to adsorb gases and organic compounds that cause unpleasant tastes and smells in water. • D (Kill germs): This is the role of disinfectants like chlorine or ozone.

    • Step 2: Evaluate the role of charcoal. Because charcoal is porous, it effectively adsorbs dissolved organic impurities, which are the primary sources of bad taste and foul odors in water.

    • Step 3: Conclusion. Since charcoal is an adsorbent, its primary function in the filter bed is to remove unpleasant odors and tastes.

    Correct Answer

    The correct option is C.

    Exam Tip

    Think of charcoal as a "sponge for smells." Whenever you see "charcoal" or "activated carbon" in a Chemistry question regarding water treatment, immediately associate it with adsorption and the removal of taste/odour. Don't confuse it with chlorine, which is for sterilization (killing germs).

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21. 21.

    The following non-metal form acidic oxides with oxygen except?

    1. A.phosphorus
    2. B.sulphur
    3. C.carbon
    4. D.chlorine

    Show answer

    Answer: D. chlorine

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22. 22.

    Using the metal activity series, the metal that can liberate hydrogen gas from steam is?

    1. A.iron
    2. B.copper
    3. C.tin
    4. D.lead

    Show answer

    Answer: A. iron

    AI explanation

    Analysis

    The question asks us to identify which of the given metals is reactive enough to displace hydrogen from steam ($H_2O_{(g)}$).

    Concept: The Metal Activity Series

    The metal activity series (or reactivity series) ranks metals based on their ability to displace hydrogen from water, steam, or acids.

    • Highly reactive metals (Potassium, Sodium, Calcium) react vigorously with cold water.
    • Moderately reactive metals (Magnesium, Aluminum, Zinc, Iron) react with steam to produce metal oxides and hydrogen gas.
    • Less reactive metals (Lead, Copper, Mercury, Silver, Gold) are below hydrogen in the activity series and generally cannot displace hydrogen from water or steam.

    The general equation for the reaction of a metal with steam is:

    $Metal + H_2O_{(g)} \rightarrow Metal\ Oxide + H_2(g)$

    Step-by-Step Solution

    1. Evaluate Copper (B): Copper is below hydrogen in the activity series. It is unreactive toward steam.
    2. Evaluate Lead (D): Lead is very low in the reactivity series. It does not react with steam.
    3. Evaluate Tin (C): While tin is more reactive than lead, it is generally considered to have a very slow or negligible reaction with steam compared to iron.
    4. Evaluate Iron (A): Iron is positioned above hydrogen in the activity series. When red-hot iron reacts with steam, it produces tri-iron tetroxide ($Fe_3O_4$) and hydrogen gas: $$3Fe_{(s)} + 4H_2O_{(g)} \rightarrow Fe_3O_4(s) + 4H_2(g)$$ This is a classic reaction taught in Nigerian secondary school chemistry curricula.

    Conclusion

    Among the options provided, iron is the only metal that effectively reacts with steam to liberate hydrogen gas.

    Exam Tip

    Remember the mnemonic for the reactivity series: Please Stop Calling Me A Careless Zebra Instead Try Learning How Copper Saves Gold. (Potassium, Sodium, Calcium, Magnesium, Aluminum, Carbon, Zinc, Iron, Tin, Lead, Hydrogen, Copper, Silver, Gold). Anything above Hydrogen can displace it from acids, but only those from Magnesium up to Iron react readily with steam!

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23. 23.

    An organic compound which decolorizes bromine water is likely to be?

    1. A.C$_3$H$_8$
    2. B.C$_2$H$_6$
    3. C.C$_4$H$_10$
    4. D.C$_2$H$_4$

    Show answer

    Answer: D. C$_2$H$_4$

    AI explanation

    Analysis

    The question asks us to identify an organic compound that decolorizes bromine water. This is a classic test for unsaturation in organic chemistry.

    Concept Explanation

    • Bromine Water Test: Bromine water ($Br_2$ in water) is reddish-brown in color. When it reacts with an unsaturated hydrocarbon (a compound containing a carbon-carbon double bond $C=C$ or triple bond $C \equiv C$), the bromine adds across the bond, forming a colorless dibromo-compound.
    • Unsaturated Hydrocarbons: These are alkenes ($C_nH_{2n}$) and alkynes ($C_nH_{2n-2}$).
    • Saturated Hydrocarbons: These are alkanes ($C_nH_{2n+2}$). Alkanes contain only single bonds and do not react with bromine water under normal conditions; therefore, they do not decolorize it.

    Step-by-Step Solution

    1. Analyze the options based on the general formula for alkanes ($C_nH_{2n+2}$): • A. $C_3H_8$: $n=3$, $2(3)+2 = 8$. This fits the formula $C_nH_{2n+2}$. It is an alkane (Propane). • B. $C_2H_6$: $n=2$, $2(2)+2 = 6$. This fits the formula $C_nH_{2n+2}$. It is an alkane (Ethane). • C. $C_4H_{10}$: $n=4$, $2(4)+2 = 10$. This fits the formula $C_nH_{2n+2}$. It is an alkane (Butane). • D. $C_2H_4$: $n=2$, $2(2) = 4$. This fits the formula $C_nH_{2n}$. It is an alkene (Ethene).

    2. Evaluate: Since options A, B, and C are alkanes, they are saturated and will not react with bromine water. Option D ($C_2H_4$) is an alkene, which is unsaturated. It will undergo an addition reaction with bromine to form 1,2-dibromoethane, causing the reddish-brown color of the bromine water to disappear.

    Conclusion

    The compound that decolorizes bromine water must be an unsaturated hydrocarbon. Among the choices provided, only $C_2H_4$ is an alkene.

    Exam Tip: Always check the ratio of Carbon to Hydrogen. If the number of Hydrogens is exactly double the number of Carbons ($C_nH_{2n}$), it is an alkene and will decolorize bromine water. If the Hydrogens are $2n+2$, it is an alkane and will not react.

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24. 24.

    In order to electroplate spoon with silver, the arrangement of the electrolytic cell is?

    1. A.the anode is a silver rod and the cathode is the spoon
    2. B.the anode is the spoon and the cathode is a silver rod
    3. C.the electrolyte is silver trioxonitrate(v)( solution and the cathode is a silver rod.
    4. D.the electrolyte is silver trioxonitrate(v) solution and the anode is the spoon

    Show answer

    Answer: A. the anode is a silver rod and the cathode is the spoon

    AI explanation

    Analysis of the Question

    This question tests your understanding of electrolysis and the principles of electroplating. Electroplating is a process where a thin layer of a metal is deposited onto another object using an electric current.

    Concept Explanation

    To electroplate an object (in this case, a spoon) with a specific metal (silver), you must follow these rules of an electrolytic cell:

    1. The Cathode (Negative Electrode): The object you want to plate must be the cathode. This is because metal ions are positively charged ($Ag^+$) and are attracted to the negative electrode, where they gain electrons (reduction) to become solid metal.
    2. The Anode (Positive Electrode): The metal you want to plate with (the source of the metal) must be the anode. As the process continues, the silver anode dissolves into the electrolyte to replenish the silver ions being used up.
    3. The Electrolyte: The solution must contain ions of the metal being plated (e.g., silver trioxonitrate(V), $AgNO_3$).

    Step-by-Step Solution

    1. Identify the goal: We want to coat the spoon with silver.
    2. Determine the Cathode: Since the spoon needs to be coated, it must be the cathode (where the silver will deposit).
    3. Determine the Anode: To keep the concentration of silver ions in the solution constant, we use a silver rod as the anode. The silver rod will oxidize ($Ag \rightarrow Ag^+ + e^-$) and provide new silver ions to the solution.
    4. Evaluate the options: • Option A: States the anode is a silver rod and the cathode is the spoon. This matches our requirement perfectly. • Option B: Swaps the roles, which would result in the spoon dissolving instead of being plated. • Options C and D: While they mention the correct electrolyte, they provide incomplete or incorrect electrode assignments.

    Conclusion

    The correct arrangement for electroplating a spoon with silver is to use a silver rod as the anode and the spoon as the cathode. This ensures that silver ions move from the anode through the electrolyte and deposit onto the spoon.

    Exam Tip: Always remember the mnemonic "PANIC" for electrolytic cells: Positive Anode, Negative Is Cathode. Also, remember that the object to be plated always goes to the cathode!

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25. 25.

    The IUPAC nomenclature of the structure is?

    1. A.3-chloro-3-methylbutane
    2. B.2,2,-dichloro-3-methylbutane
    3. C.3-methylchlorobutane
    4. D.2-chloro-2-methylbutane

    Show answer

    Answer: A. 3-chloro-3-methylbutane

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26. 26.

    Addition of sodium chloride to water to form a solution would  lead to?

    1. A.increase in freezing point and increase the boiling point
    2. B.increase in freezing point and decrease the boiling point
    3. C.decrease in freezing point and decrease the boiling point
    4. D.decrease in freezing point and increase the boiling point

    Show answer

    Answer: D. decrease in freezing point and increase the boiling point

    AI explanation

    Analysis of the Question

    This question tests your understanding of Colligative Properties of solutions. Specifically, it asks how the addition of a non-volatile solute (sodium chloride, NaCl) affects the physical properties of a solvent (water).

    Concept Explanation

    Colligative properties are properties of a solution that depend on the number of solute particles present, rather than the nature of the solute itself. When you add a solute like salt to a pure solvent like water, two major changes occur:

    1. Boiling Point Elevation: The presence of solute particles interferes with the solvent molecules escaping into the vapor phase. To reach the vapor pressure required for boiling, the solution must be heated to a higher temperature than the pure solvent. Therefore, the boiling point increases.
    2. Freezing Point Depression: The solute particles disrupt the formation of the ordered crystalline structure of the solid solvent. Because it is harder for the solvent to freeze, the temperature must be lowered further to turn the solution into a solid. Therefore, the freezing point decreases.

    Step-by-Step Solution

    1. Identify the solute and solvent: Sodium chloride (NaCl) is the solute, and water ($H_2O$) is the solvent.
    2. Apply Boiling Point Elevation: Adding NaCl to water makes it harder for water to boil. Thus, the boiling point of the solution will be higher than $100^\circ C$. This is an increase.
    3. Apply Freezing Point Depression: Adding NaCl to water makes it harder for water to freeze. Thus, the freezing point of the solution will be lower than $0^\circ C$. This is a decrease.
    4. Combine the findings: We are looking for an option that states a decrease in freezing point and an increase in boiling point.

    Comparing this to your options:

    • Option A: Incorrect (Freezing point doesn't increase).
    • Option B: Incorrect (Both are wrong).
    • Option C: Incorrect (Boiling point doesn't decrease).
    • Option D: Correct (Matches our findings).

    Exam Tip

    Think of the "Salt on the Road" trick: In cold countries, salt is spread on icy roads during winter. Why? Because the salt lowers the freezing point of the ice, causing it to melt at temperatures where it would normally remain frozen. This helps you remember that adding salt decreases the freezing point!

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27. 27.

    In which of the following will hydrogen form ionic compound?

    1. A.HCL
    2. B.NaH
    3. C.NH$_3$
    4. D.CH$_4$

    Show answer

    Answer: B. NaH

    AI explanation

    Analysis

    The question asks us to identify which of the given compounds contains hydrogen in an ionic bond. To solve this, we must look at the electronegativity difference between hydrogen and the element it is bonded to.

    Concept Explanation

    • Ionic Compounds: These are formed when there is a large difference in electronegativity between two atoms, usually a metal and a non-metal. The metal loses an electron to become a cation, and the non-metal gains that electron to become an anion.
    • Hydrogen's Behavior: Hydrogen is unique. It can form covalent bonds with non-metals (by sharing electrons) or ionic bonds with highly electropositive metals (Group 1 and Group 2 elements). When hydrogen bonds with a metal, it gains an electron to form a hydride ion ($H^-$), resulting in an ionic compound.

    Step-by-Step Solution

    1. Analyze Option A (HCl): Hydrogen and Chlorine are both non-metals. They share electrons to form a covalent bond.
    2. Analyze Option B (NaH): Sodium (Na) is a Group 1 alkali metal (highly electropositive). Hydrogen is a non-metal. When they react, Sodium transfers its valence electron to Hydrogen. This creates $Na^+$ and $H^-$ ions held together by electrostatic forces. This is an ionic hydride.
    3. Analyze Option C (NH$_3$): Nitrogen and Hydrogen are both non-metals. They share electrons to form polar covalent bonds.
    4. Analyze Option D (CH$_4$): Carbon and Hydrogen are both non-metals. They share electrons to form non-polar covalent bonds.

    Conclusion

    Since Sodium is a metal and Hydrogen acts as the anion in this structure, Sodium Hydride (NaH) is the only ionic compound listed.

    Exam Tip: Whenever you see a hydride of a Group 1 or Group 2 metal (like LiH, NaH, KH, or $CaH_2$), always remember they are ionic. If hydrogen is bonded to a non-metal (like C, N, O, or Cl), it is almost certainly a covalent compound.

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28. 28.

    An organic compound with fishy smell is likely to have a general formula?

    1. A.RCONHR$^1$
    2. B.RCONH$_2$
    3. C.RNH$_2$
    4. D.RCOR$^1$

    Show answer

    Answer: C. RNH$_2$

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29. 29.

    What volume of (dm$^3$) of water will be added to 10dm$^3$ of 2.0 mol/dm$^3$ HCL acid solution to give a final solution of 0.5 mol/dm$^3$?

    1. A.30
    2. B.40
    3. C.20
    4. D.50

    Show answer

    Answer: A. 30

    AI explanation

    Analysis

    To solve this problem, we use the dilution formula. When you add water to a solution, the number of moles of the solute (HCl) remains constant, but the volume and concentration change.

    Concept

    The dilution formula is:

    $C_1V_1 = C_2V_2$

    Where:

    • $C_1$ = Initial concentration (2.0 mol/dm³)
    • $V_1$ = Initial volume (10 dm³)
    • $C_2$ = Final concentration (0.5 mol/dm³)
    • $V_2$ = Final total volume (Initial volume + Volume of water added)

    Solution

    Step 1: Calculate the final total volume ($V_2$) Using the formula $C_1V_1 = C_2V_2$: $2.0 \times 10 = 0.5 \times V_2$ $20 = 0.5 \times V_2$

    Divide both sides by 0.5: $V_2 = \frac{20}{0.5}$ $V_2 = 40 \text{ dm}^3$

    Step 2: Calculate the volume of water added The total final volume ($V_2$) is the sum of the initial volume ($V_1$) and the volume of water added ($V_{added}$). $V_2 = V_1 + V_{added}$ $40 = 10 + V_{added}$ $V_{added} = 40 - 10$ $V_{added} = 30 \text{ dm}^3$

    Conclusion

    The volume of water to be added is 30 dm³. This matches option A.

    Exam Tip

    Always distinguish between the final volume ($V_2$) and the volume added. Many students stop at 40 dm³ and choose that as the answer, forgetting that the question asks for the volume of water added to the existing 10 dm³. Always read the question carefully to see if it asks for the final volume or the volume to be added.

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30. 30.

    The sulphide that is commonly used in coating electric fluorescent tubes is?

    1. A.iron(ii)Sulphide
    2. B.tin(ii)sulphide
    3. C.Zinc Sulphide
    4. D.lead(iv) Sulphide

    Show answer

    Answer: C. Zinc Sulphide

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31. 31.

    A colored gas that is known to be poisonous and can readily damage the mucous lining of the lungs is?

    1. A.hydrogen sulphide
    2. B.carbon(ii)oxide
    3. C.chlorine
    4. D.sulphur(iv)oxide

    Show answer

    Answer: C. chlorine

    AI explanation

    Analysis

    The question asks us to identify a specific gas based on three characteristics:

    1. It is colored.
    2. It is poisonous.
    3. It specifically damages the mucous lining of the lungs.

    Concept Explanation

    To solve this, let's look at the properties of the gases listed:

    • Hydrogen sulphide ($H_2S$): A colorless gas with a rotten egg smell. It is toxic, but it is not known primarily for its color.
    • Carbon(II) oxide ($CO$): A colorless, odorless, and highly poisonous gas. It binds to hemoglobin in the blood, preventing oxygen transport, but it is not a colored gas.
    • Chlorine ($Cl_2$): A pale greenish-yellow gas. It is highly reactive and toxic. Because it is a strong oxidizing agent, when inhaled, it reacts with the moisture in the respiratory tract to form hydrochloric acid ($HCl$) and hypochlorous acid ($HOCl$). These acids are highly corrosive and cause severe damage to the mucous membranes of the lungs.
    • Sulphur(IV) oxide ($SO_2$): A colorless gas with a pungent, choking smell. While it is an irritant to the lungs, it is not colored.

    Step-by-Step Solution

    1. Eliminate colorless gases: Options A, B, and D are all colorless gases. This immediately narrows our search down to Option C.
    2. Verify the properties of Chlorine: • Color: Chlorine is distinctly greenish-yellow. • Toxicity: It is a well-known poisonous gas used historically in chemical warfare. • Effect on lungs: As explained above, its reaction with water in the lungs creates acidic conditions that destroy the delicate mucous lining, leading to pulmonary edema (fluid in the lungs).

    Conclusion

    Based on the physical property of being a "colored gas" and the physiological effect on the respiratory system, Chlorine is the correct answer.

    Exam Tip: Whenever you see a question about a "greenish-yellow" gas in Chemistry, always think of Chlorine. It is a classic JAMB favorite!

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32. 32.This question needs a diagram, table or passage that we don't have yet, so it isn't shown.

33. 33.

    In the preparation of salts, the method employed will depend on the?

    1. A.composition
    2. B.dissociating ability
    3. C.stability to heat
    4. D.precipitating ability

    Show answer

    Answer: C. stability to heat

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34. 34.

    On the basis of the electrochemical series, which of these ions will show the greater tendency to be discharged at the cathode in an electrolytic cell

    1. A.cu$^{2+}$
    2. B.sn$^{2+}$
    3. C.fe$^{2+}$
    4. D.zn$^{2+}$

    Show answer

    Answer: A. cu$^{2+}$

    AI explanation

    Analysis

    The question asks us to identify which of the given metal ions ($Cu^{2+}$, $Sn^{2+}$, $Fe^{2+}$, $Zn^{2+}$) is most easily discharged at the cathode during electrolysis.

    Concept: The Electrochemical Series

    In an electrolytic cell, the electrochemical series (or activity series) dictates the ease of discharge of ions.

    • At the cathode: Cations (positive ions) compete to gain electrons (reduction). The ion that is lower in the electrochemical series has a greater tendency to be discharged because it is more easily reduced (it has a more positive standard electrode potential).

    The general order of discharge for common cations at the cathode is: $K^+ < Na^+ < Ca^{2+} < Mg^{2+} < Al^{3+} < Zn^{2+} < Fe^{2+} < Sn^{2+} < Pb^{2+} < H^+ < \mathbf{Cu^{2+}} < Ag^+ < Au^{3+}$

    Step-by-Step Solution

    1. Understand the Rule: The further down an element is in the electrochemical series, the easier it is for its ion to gain electrons and be discharged as a metal at the cathode.
    2. Locate the ions: • $Zn^{2+}$ (Zinc) is relatively high in the series. • $Fe^{2+}$ (Iron) is below Zinc. • $Sn^{2+}$ (Tin) is below Iron. • $Cu^{2+}$ (Copper) is significantly lower than all the other options provided.
    3. Compare: Since $Cu^{2+}$ is the lowest among the options listed, it requires the least amount of energy to be reduced to copper metal ($Cu$). Therefore, it has the greatest tendency to be discharged.

    Conclusion

    Based on the electrochemical series, $Cu^{2+}$ is the most easily discharged ion among the choices provided.

    Exam Tip

    Remember the mnemonic for the electrochemical series of metals: "Please Stop Calling Me A Zebra In Large Heavy Cages, Make Sure Copper Saves Gold." (Potassium, Sodium, Calcium, Magnesium, Aluminium, Zinc, Iron, Lead, Hydrogen, Copper, Silver, Gold). The further right (or down) you go, the easier the ion is to discharge at the cathode!

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35. 35.

    Crude petroleum is converted to useful products by the process of?

    1. A.fractional crystallization
    2. B.fractional distillation
    3. C.filtration
    4. D.chromatography

    Show answer

    Answer: B. fractional distillation

    AI explanation

    Analysis

    The question asks for the specific industrial process used to separate crude oil into its various useful components (such as petrol, kerosene, diesel, and bitumen).

    Concept Explanation

    Crude oil is a complex mixture of hydrocarbons with different boiling points. Because these components have different molecular sizes and weights, they vaporize and condense at different temperatures. To separate them, we use a technique called fractional distillation.

    In this process:

    1. The crude oil is heated in a furnace.
    2. The vapors enter a tall fractionating column.
    3. As the vapors rise, the temperature of the column decreases.
    4. Components with higher boiling points condense near the bottom, while those with lower boiling points rise higher before condensing.
    5. This allows for the collection of different "fractions" at different levels of the column.

    Step-by-Step Solution

    • Option A (Fractional crystallization): This is used to separate solid mixtures based on differences in solubility at different temperatures. It is not suitable for liquid crude oil.
    • Option B (Fractional distillation): This is the standard industrial method for separating liquids that are miscible and have different boiling points, which perfectly describes the refining of crude oil.
    • Option C (Filtration): This is used to separate an insoluble solid from a liquid. It cannot separate the various hydrocarbons found in crude oil.
    • Option D (Chromatography): This is used to separate small amounts of mixtures based on their movement through a stationary phase. It is a laboratory technique for analysis, not an industrial method for refining large volumes of petroleum.

    Conclusion

    Since crude oil is a mixture of hydrocarbons with varying boiling points, fractional distillation is the correct industrial process used to refine it.

    Exam Tip: Remember that "Fractional Distillation" is for liquids with different boiling points, while "Fractional Crystallization" is for solids with different solubilities. Don't mix them up!

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36. 36.

    An organic compound contains 69% carbon, 15.3% hydrogen and 30.7% oxygen. Calculate the the empirical formula [C=12, H = 1, O = 16]

    1. A.C$_4$H$_12$O
    2. B.C$_3$H$_9$O
    3. C.C$_4$H$_9$O
    4. D.C$_3$H$_8$O

    Show answer

    Answer: D. C$_3$H$_8$O

    AI explanation

    To find the empirical formula of this organic compound, we need to determine the simplest whole-number ratio of the atoms present. We follow these steps:

    1. Analyze the composition

    • Carbon (C): 69%
    • Hydrogen (H): 15.3%
    • Oxygen (O): 30.7%

    2. Calculate the number of moles

    Assume we have 100g of the compound. This means we have 69g of C, 15.3g of H, and 30.7g of O. We divide the mass of each element by its relative atomic mass:

    • Moles of C: $\frac{69}{12} = 5.75$
    • Moles of H: $\frac{15.3}{1} = 15.3$
    • Moles of O: $\frac{30.7}{16} = 1.91875 \approx 1.92$

    3. Find the simplest ratio

    Divide each mole value by the smallest value obtained (which is 1.92):

    • Ratio of C: $\frac{5.75}{1.92} \approx 2.99 \approx 3$
    • Ratio of H: $\frac{15.3}{1.92} \approx 7.96 \approx 8$
    • Ratio of O: $\frac{1.92}{1.92} = 1$

    4. Determine the Empirical Formula

    Based on the ratios calculated, we have 3 atoms of Carbon, 8 atoms of Hydrogen, and 1 atom of Oxygen.

    The empirical formula is C$_3$H$_8$O.

    Note on the calculation: While the math leads us to C$_3$H$_8$O, it is important to note that in chemistry, the sum of percentages must equal 100%. Here, $69 + 15.3 + 30.7 = 115$. This suggests a slight error in the question's provided percentages. However, by using the ratio method, we identify the most consistent empirical formula provided in the options.

    Exam Tip: When calculating empirical formulas, if your division results in a decimal like 0.5, multiply all ratios by 2 to get a whole number. If you get 0.33, multiply by 3. Always round to the nearest whole number only if the decimal is very close (e.g., 2.99 to 3).

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37. 37.

    How many bonding pair are present in carbon(iv)oxide?

    1. A.4
    2. B.3
    3. C.2
    4. D.1

    Show answer

    Answer: A. 4

    AI explanation

    Analysis

    The question asks for the number of bonding pairs in a molecule of carbon(IV) oxide ($CO_2$). A bonding pair refers to a pair of electrons shared between two atoms to form a covalent bond.

    Concept

    Carbon(IV) oxide ($CO_2$) is a linear molecule. To determine the number of bonding pairs, we look at its Lewis structure:

    1. Carbon (C) is in Group 4, meaning it has 4 valence electrons. It needs 4 more to complete its octet.
    2. Oxygen (O) is in Group 6, meaning it has 6 valence electrons. Each oxygen atom needs 2 more to complete its octet.
    3. To achieve stability, the carbon atom forms a double bond with each of the two oxygen atoms.

    Solution

    • Structure: $O = C = O$
    • Bonding: • The bond between Carbon and the first Oxygen consists of 2 shared pairs of electrons (a double bond). • The bond between Carbon and the second Oxygen also consists of 2 shared pairs of electrons (a double bond).
    • Calculation: • Number of bonding pairs = (Pairs in first double bond) + (Pairs in second double bond) • Number of bonding pairs = 2 + 2 = 4 bonding pairs.

    Conclusion

    In the $CO_2$ molecule, there are 4 shared pairs of electrons (bonding pairs) in total, distributed as two double bonds.

    Exam Tip

    When counting bonding pairs, remember that a single bond counts as 1 pair, a double bond counts as 2 pairs, and a triple bond counts as 3 pairs. Always draw the Lewis structure first to avoid missing any bonds!

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38. 38.

    2H$_2$ + O$_2$ → 2H$_2$O From the equation above, calculate the volume of unreacted oxygen gas if a mixture of 50cm$^3$ of hydroden and 75cm$^3$ of oxygen are involved

    1. A.85cm$^3$
    2. B.50cm$^3$
    3. C.125cm$^3$
    4. D.55cm$^3$

    Show answer

    Answer: B. 50cm$^3$

    AI explanation

    Analysis

    To solve this problem, we use the principle of Gay-Lussac’s Law of Combining Volumes, which states that gases react in simple whole-number ratios by volume under the same conditions of temperature and pressure.

    Concept

    The balanced chemical equation is: 2H$_2$(g) + O$_2$(g) → 2H$_2$O(g)

    From the stoichiometry of the equation:

    • 2 volumes of Hydrogen (H$_2$) react with 1 volume of Oxygen (O$_2$).
    • This means the ratio of H$_2$ to O$_2$ is 2:1.

    Step-by-Step Solution

    1. Determine the required volume of Oxygen: Since 2 volumes of H$_2$ require 1 volume of O$_2$, then 50 cm$^3$ of H$_2$ will require: $$\text{Volume of O}_2 \text{ required} = \frac{1}{2} \times 50 \text{ cm}^3 = 25 \text{ cm}^3$$

    2. Calculate the unreacted (excess) Oxygen: You were given 75 cm$^3$ of oxygen initially. $$\text{Unreacted O}_2 = \text{Initial Volume} - \text{Volume Used}$$ $$\text{Unreacted O}_2 = 75 \text{ cm}^3 - 25 \text{ cm}^3 = 50 \text{ cm}^3$$

    Conclusion

    The volume of oxygen remaining after the reaction is 50 cm$^3$.

    Exam Tip: Always check the mole ratio from the balanced equation first. If you have two different volumes given for reactants, one is always in "excess." The reactant that runs out first is the "limiting reagent"—always base your calculations on the limiting reagent!

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39. 39.

    N$_2$O$_4$ ⇔ 2NO$_2$          (Δ = -ve) From the reaction above, which of these conditions would produce the highest equilibrium yield for N$_2$O$_4$?

    1. A.Low temperature and high pressure
    2. B.Low temperature and low pressure
    3. C.high temperature and low pressure
    4. D.high temperature and high pressure

    Show answer

    Answer: D. high temperature and high pressure

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40. 40.

    Zn + 2HCL → ZnCl$_2$ + H$_2$  What happens to zinc in the above reaction?

    1. A.oxidized
    2. B.a reactant
    3. C.reduced
    4. D.a metal

    Show answer

    Answer: A. oxidized

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