WAEC Chemistry 2022
Questions & Answers

A student might mistakenly pick ethanoic acid or propanol, confusing fermentation products with oxidation or synthesis derivatives. The chemical breakdown of glucose by yeast yields ethanol alongside carbon(IV) oxide gas as a by-product, represented by the chemical equation where sugar converts into alcohol and gas, with the latter causing effervescence. Common mistake: Confusing the gaseous by-product of sugar fermentation with organic acid or alcohol derivatives.

A student might choose glucose or fructose, overlooking the fact that those are individual building blocks rather than condensation products. Maltose is a disaccharide that forms specifically through the condensation or dehydration reaction of two glucose monosaccharides, a process that also releases water molecules. Common mistake: Confusing individual monosaccharide building blocks with disaccharides formed via condensation.

A student might mistakenly select the hardness of the acidic water, confusing mineral-induced hardness with proton interactions. Soap consists of sodium carboxylate, which reacts with hydrogen ions in acidic water to form insoluble fatty acids. This reaction precipitates the soap out of solution, significantly reducing its lathering and cleansing power. Common mistake: Attributing poor soap performance in acidic solutions to mineral hardness rather than hydrogen ion precipitation.

A student might pick nylon or protein, confusing synthetic polyamides or natural macromolecules with addition polymers. Polyethene is an addition polymer created by joining ethene monomers without eliminating small molecules. In contrast, nylon, proteins, and starch are all condensation polymers that involve the elimination of water during formation. Common mistake: Confusing addition polymers formed without small molecule loss with condensation polymers.

A student might select one faraday or one ampere by misinterpreting the ionic charge as a one-to-one electron ratio. The reduction half-reaction for aluminium is Al³⁺ + 3e⁻ → Al, which requires three moles of electrons for every single mole of aluminium deposited. Since one faraday equals one mole of electrons, a total of three faradays is required. Common mistake: Forgetting to account for the ionic valency and matching electron moles in faraday calculations.

A student might select benzene or hexane, failing to distinguish between saturated hydrocarbons, aromatic rings, and unsaturated alkenes. Hexene contains a reactive carbon-carbon double bond, enabling it to undergo rapid electrophilic addition with bromine and instantly decolorize it without needing a catalyst. Common mistake: Assuming stable aromatic rings or saturated alkanes react as rapidly with bromine as alkenes do.

A student might choose aqueous potassium tetraoxomanganate(VII) or bromine, confusing oxidation or halogenation tests with hydration manufacturing routes. Alkanols are manufactured from alkenes through acid-catalyzed hydration, where the alkene reacts initially with concentrated tetraoxosulphate(VI) acid to form an alkyl hydrogensulfate before reacting with water. Common mistake: Confusing the initial acid-catalyzed addition step of industrial hydration with oxidation or halogenation.

A student might mistakenly select the hydrogen gas pressure or the platinum electrode usage, assuming those parameters are variable. The standard hydrogen electrode operates under strict standardized conditions, featuring 1 atm of hydrogen gas, a 1 moldm⁻³ concentration of hydrogen ions, and a platinum electrode, but its designated temperature is 25°C rather than 20°C. Common mistake: Mixing up the exact standardized temperature requirement of 25 degrees Celsius for the standard hydrogen electrode.

A student might choose MO or MO₂ by making calculation errors when converting mass proportions into moles. Dividing the given mass of element M by its atomic mass gives 0.5 moles, while dividing the oxygen mass by its atomic mass yields 1.5 moles. Simplifying the molar ratio of 0.5 to 1.5 gives a 1 to 3 ratio, establishing the empirical formula as MO₃. Common mistake: Incorrectly simplifying mole ratios when determining chemical formulas from mass data.

A student might select chlorine and sodium, confusing the electrolysis products of dilute solutions with those of concentrated sodium chloride brine. During the electrolysis of dilute sodium chloride using carbon electrodes, water molecules undergo oxidation at the anode to produce oxygen gas and reduction at the cathode to yield hydrogen gas. Common mistake: Forgetting that water preferential discharge alters electrolysis products when dealing with dilute solutions.

A student might select 12C by multiplying current directly by minutes without converting time units into standard seconds. Charge is calculated as current multiplied by time in seconds, so multiplying 0.20 amperes by 3600 seconds yields a total quantity of 720 coulombs. Common mistake: Failing to convert time from minutes into seconds when calculating electrical charge.

A student might select a reducing agent or a weak acid, confusing acidic strength or reduction reactions with bleaching mechanisms. Oxochlorate(I) acid acts as a bleaching agent specifically because it is an oxidizing agent that releases nascent oxygen, which destroys color pigments in dyes through oxidation. Common mistake: Attributing the bleaching action of hypochlorous acid to its acidic properties rather than its oxidizing capability.

A student might select option B or C by starting their numbering from the wrong end of the carbon chain or misordering alphabetical priorities. The longest carbon chain contains six carbons, with methyl substituents located at positions 2 and 4 and a chlorine atom at position 3. Numbering from the left provides the lowest possible locants, yielding the IUPAC name 3-chloro-2,4-dimethylhexane. Common mistake: Failing to number the longest carbon chain from the end that gives the lowest locant numbers.

1) Distractor check: Students might select option A because they know acidified K₂Cr₂O₇ is another common oxidizing agent that changes color upon reduction, but it turns green instead of colorless with sulfur dioxide. 2) Reasoning to the answer: When a sample of salt reacts with dilute hydrochloric acid, sulfur dioxide gas is released via the chemical transformation represented by Na₂SO₃ + 2HCl → 2NaCl + H₂O + SO₂. Because sulfur dioxide acts as a reducing agent in this context, it causes purple permanganate solution to transform into colorless Mn²⁺ ions in an acidic environment. 3) Common mistake: Confusing the final color change of potassium dichromate (which turns green) with that of potassium permanganate (which becomes colorless).

1) Distractor check: A student could easily choose option B or D by only optimizing one variable—either concentration or surface area—while ignoring that maximum reaction rate requires both factors simultaneously. 2) Reasoning to the answer: Reaction rate speeds up significantly when reactants possess a larger surface area, as seen with powdered marble over coarser chips, and when the concentration of the acid is higher, such as 2.5 moldm⁻³ compared to 2.0 moldm⁻³. Utilizing powdered marble together with 2.5 moldm⁻³ hydrochloric acid successfully maximizes both of these rate-accelerating factors at once. 3) Common mistake: Overlooking that combining both a high concentration and a maximized surface area yields a faster rate than optimizing just one parameter.

1) Distractor check: Option C is a tempting choice for students who assume that higher kinetic energy uniformly helps all solutes dissolve more readily in liquid solvents regardless of their physical state. 2) Reasoning to the answer: Elevated temperatures supply the necessary energy to break apart crystal lattice forces, which raises solid solubility in a liquid. Conversely, for gaseous solutes, heating the solution weakens the existing intermolecular forces and drives the gas out of solution, as predicted by Le Chatelier's principle for exothermic dissolution processes. 3) Common mistake: Assuming that temperature affects the solubility of solids and gases in the exact same direction.

1) Distractor check: Option B is a frequent point of confusion because barium sulfite also forms a white precipitate with barium chloride, but it fails to generate rapid effervescence when treated with dilute acid. 2) Reasoning to the answer: Adding aqueous barium chloride to salt X yields a white precipitate of barium carbonate, which remains insoluble in pure water. Upon the introduction of dilute hydrochloric acid, this precipitate decomposes vigorously in the reaction BaCO₃ + 2HCl → BaCl₂ + H₂O + CO₂ to produce rapid effervescence from carbon dioxide gas. 3) Common mistake: Confusing sulfite and carbonate precipitates, forgetting that only carbonate produces rapid effervescence with dilute acid.

1) Distractor check: A student might choose option D by confusing reactants with products or incorrectly assuming that ionization must happen before any chemical change can initiate. 2) Reasoning to the answer: Chemical transformations cannot proceed unless existing bonds within the reactant molecules are first cleaved, an initial step that demands a specific amount of activation energy. Once these reactant bonds break, the system can proceed to establish new bonds that constitute the final products. 3) Common mistake: Forgetting that bond breakage is an energy-demanding prerequisite step that must happen to the reactants before any product formation can begin.

1) Distractor check: Students could mistakenly pick option A because calcium oxide is basic, leading them to misidentify silicon(IV) oxide as sharing that same classification. 2) Reasoning to the answer: Silicon(IV) oxide functions as a non-metal oxide that accepts electron pairs from bases, allowing it to react directly with basic calcium oxide to yield the salt calcium metasilicate in the equation CaO + SiO₂ → CaSiO₃. This behavior defines it clearly as an acidic oxide. 3) Common mistake: Assuming that because an oxide reacts with a base, it must also be basic rather than acting as an acidic counterpart.

1) Distractor check: Option A is a common erroneous pick because students often overlook the presence of multiple replaceable hydrogen atoms in polybasic mineral acids. 2) Reasoning to the answer: Trioxonitrate(V) acid possesses only one replaceable hydrogen ion per molecule, making it monobasic and capable of generating exclusively normal salts like sodium nitrate. On the other hand, the other choices are polybasic acids that can retain hydrogen during partial neutralization to produce acid salts alongside normal salts. 3) Common mistake: Failing to check the basicity (number of replaceable hydrogens) of an acid when predicting whether it can form acid salts.

1) Distractor check: Option D is a frequent wrong choice for students who calculate the mole fraction of nitrogen instead of oxygen or confuse the individual gas volumes. 2) Reasoning to the answer: The total volume of the gaseous mixture combines to 1000 cm³, meaning the mole fraction contributed by oxygen is equal to 100 divided by 1000, which evaluates to 0.1. Applying Dalton's law of partial pressures under standard temperature and pressure conditions, where total pressure equals 1 atm, the partial pressure of oxygen becomes 0.1 multiplied by 1 atm, resulting in 0.1 atm. 3) Common mistake: Dividing by the wrong volume or mixing up the gas components when determining the mole fraction for partial pressure calculations.

1) Distractor check: Option A or B might be chosen because students know that graphite conducts electricity via free electrons, incorrectly linking electrical conductivity to its lubricating properties. 2) Reasoning to the answer: Graphite is structured such that its carbon atoms are arranged in distinct planes connected by weak intermolecular van der Waals forces. These sheets can easily slide past one another with minimal friction, making the substance an effective dry lubricant. 3) Common mistake: Attributing physical macroscopic traits like lubricativity to electronic mobility rather than the weak interlayer bonding forces.

1) Distractor check: Option A is a distractor because nitrogen dioxide reacts with water to form acids, leading unwary students to misclassify nitrogen-containing gases. 2) Reasoning to the answer: When ammonia gas is dissolved in water, it undergoes a reaction to produce ammonium hydroxide, which acts as a weak base and imparts an alkaline nature to the solution. The remaining choices consist of neutral or acidic non-metal oxides that do not generate basic aqueous solutions. 3) Common mistake: Assuming all nitrogen oxides or nitrogen-containing gases share acidic properties.

1) Distractor check: Option B is a classic trap because students frequently confuse dynamic equilibrium with having identical concentrations of both reactants and products. 2) Reasoning to the answer: A system achieves true dynamic chemical equilibrium when the rate at which the forward reaction proceeds exactly matches the rate of the reverse reaction, which keeps macroscopic concentrations constant over time. Catalysts only alter the speed of both directions equally without disturbing equilibrium concentrations, while temperature changes can shift the position of equilibrium. 3) Common mistake: Equating equal reaction rates with equal concentrations of reactants and products.

1) Distractor check: Option A is a common error for students who confuse how endothermic versus exothermic systems respond to external thermal changes. 2) Reasoning to the answer: The provided synthesis of ammonia is an exothermic process with a negative enthalpy change of -92 kJ, meaning heat can be considered a product of the reaction. Raising the temperature drives the system to absorb the excess heat by shifting the equilibrium position in the endothermic reverse direction, which ultimately reduces the overall yield of ammonia. 3) Common mistake: Forgetting that increasing the temperature of an exothermic reaction favors the reverse pathway and reduces product yield.

1) Distractor check: Option A is an attractive distractor for students who know extreme compression can liquefy gases, even though ordinary isothermal compression in a syringe simply increases pressure without hitting liquefaction thresholds. 2) Reasoning to the answer: According to Boyle's law, when the temperature of a confined gas remains constant, reducing its volume forces the particles closer together into a restricted space. This confinement increases the frequency and force of molecular collisions with the container walls, resulting in a higher pressure. 3) Common mistake: Assuming minor mechanical compression at room temperature is sufficient to cause gas liquefaction.

1) Distractor check: Option A is a partial trap for students who correctly identify that liquids preserve their volume but forget that they also exhibit slight compressibility under varying external pressures. 2) Reasoning to the answer: Liquids preserve a fixed volume at any given constant temperature, aligning with statement I, while statement II is false because they adopt the shape of whatever container holds them. Statement III is incorrect because liquids do diffuse, albeit very slowly, and statement IV is true because changes in external pressure can produce a minimal variation in liquid volume due to slight compressibility. 3) Common mistake: Overlooking the slight compressibility of liquids under pressure changes.

1) Distractor check: Option C or D might be guessed by students who fail to carefully balance the stoichiometric coefficients before comparing the molar amounts. 2) Reasoning to the answer: The balanced equation for the chemical change is 4HCl + O₂ → 2Cl₂ + 2H₂O, which shows that four moles of hydrogen chloride react to generate two moles of water. Reducing this 4:2 mole ratio down to its simplest terms yields a ratio of 2:1 for hydrogen chloride to water. 3) Common mistake: Reading the coefficients straight from an unbalanced or hastily interpreted reaction equation.

1) Distractor check: Option D is a typical calculation error for students who mix up the numerator and denominator or misplace the decimal point during ideal gas law evaluations. 2) Reasoning to the answer: Applying the ideal gas equation rearranged for moles, n = PV / RT, we substitute the given values to get n = (10 atm × 8.2 dm³) / (0.082 atm dm³ mol⁻¹ K⁻¹ × 320 K). Evaluating the numerator yields 82 and the denominator gives 26.24, which divides out to approximately 3.13 moles. 3) Common mistake: Inverting the gas constant or pressure-volume terms when isolating moles in the ideal gas equation.

1) Distractor check: Option D is often picked by students who forget to convert the solution volume from cubic centimeters into cubic decimeters when calculating concentration. 2) Reasoning to the answer: First, determine the number of moles by dividing the mass of potassium nitrate by its molar mass of 101 g/mol, yielding 5.05 / 101 = 0.05 mol. Next, convert the 50 cm³ volume into cubic decimeters by dividing by 1000 to get 0.05 dm³, and divide the moles by this volume to find a solubility of 1.0 mol dm⁻³. 3) Common mistake: Forgetting to convert volume from cm³ to dm³, leading to a concentration calculation that is off by a factor of one thousand.

1) Distractor check: Option A is tempting because students might confuse noble metals like silver with reactive metals that sit higher up in the electrochemical series. 2) Reasoning to the answer: Zinc occupies a position higher than copper on the metal reactivity series, enabling it to spontaneously donate electrons to copper ions in the displacement reaction Zn + Cu²⁺ → Zn²⁺ + Cu. Metals like silver, gold, and mercury reside below copper and lack the reducing power required to displace it. 3) Common mistake: Confusing the relative positions of zinc and precious metals like silver or gold on the reactivity series.

1) Distractor check: Option A is a frequent error for students who calculate the mass percentage of the bicarbonate ion group as a whole instead of isolating the carbon atoms alone. 2) Reasoning to the answer: The total molar mass of calcium hydrogen carbonate, Ca(HCO₃)₂, is calculated as 40 + 2(1 + 12 + 48), which totals 162 g/mol. Since there are two carbon atoms contributing a combined mass of 24 g/mol, the percentage composition is found by dividing 24 by 162 and multiplying by 100 to get 14.8%. 3) Common mistake: Forgetting to multiply the subscript outside the parentheses by the individual atomic masses inside when finding total molar mass or element contribution.

1) Distractor check: Option A is a frequent trap because students often confuse strong intramolecular covalent bonds found inside molecules with forces acting between separate molecules. 2) Reasoning to the answer: Hydrogen bonds represent relatively weak attractive forces operating between separate molecules, such as water molecules, rather than the chemical bonds holding atoms together internally. Covalent, ionic, and metallic bonds are all classified as intramolecular forces binding constituents within a compound. 3) Common mistake: Confusing intramolecular bonds (like covalent or ionic bonds) with intermolecular forces (like hydrogen bonding).

1) Distractor check: Option D is a common misconception for students who assume every second-period element automatically expands its bonding capacity to four pairs or four single bonds. 2) Reasoning to the answer: Nitrogen possesses a valence shell electronic configuration of 2s²2p³, containing five electrons that allow it to form three single or multiple covalent bonds while retaining a lone pair in molecules like ammonia. Because it lacks low-lying vacant d-orbitals, it cannot expand its octet to routinely form four covalent bonds under normal circumstances. 3) Common mistake: Assuming nitrogen can form four covalent bonds just like carbon without accounting for its valence electron count and lone pair.

1) Distractor check: Option A is selected by students who misnumber the carbon chain from the wrong end and fail to locate the double bond and substituent properly. 2) Reasoning to the answer: Tracing the longest continuous carbon chain containing the double bond yields four carbon atoms, making it a butane derivative. Numbering begins from the end closest to the double bond to give it the lowest possible locant (carbon-1), which places a methyl group at carbon-3, resulting in the IUPAC name 3-methylbut-1-ene. 3) Common mistake: Numbering the carbon chain from the end closest to the substituent branch instead of giving priority to the principal functional group or double bond.

1) Distractor check: Option A is often chosen because students notice a general trend with atomic numbers, failing to recognize that nuclear charge is the direct mechanistic cause. 2) Reasoning to the answer: Moving across a period, protons are added to the nucleus while electrons fill the same principal energy shell, leading to a steady rise in the effective nuclear charge. This stronger positive pull holds the valence electrons tighter, requiring more energy to remove them and causing ionization energy to increase. 3) Common mistake: Attributing periodic trends solely to increasing atomic number without considering the underlying effective nuclear charge.

1) Distractor check: Option A is a distractor for students who confuse the chemical behavior of metallic oxides with non-metallic oxides regarding acidity and basicity. 2) Reasoning to the answer: Typical metallic elements react to form ionic chlorides, satisfying statement II, and they occupy a position above hydrogen in the reactivity series which allows them to displace hydrogen gas from dilute hydrochloric acid per statement IV. Statement I describes non-metal oxides, and statement III applies mainly to transition metals rather than defining all metals. 3) Common mistake: Confusing the properties of acidic non-metal oxides with basic metallic oxides.

1) Distractor check: Option D is a common trap because students mistake the ground-state carbon configuration for the excited state involved in bonding. 2) Reasoning to the answer: In its ground state, carbon has the configuration 1s²2s²2p² with only two unpaired electrons. To achieve tetravalency, one electron from the 2s orbital is promoted into the vacant 2p_z orbital, yielding an excited state configuration of 1s²2s¹2p_x¹2p_y¹2p_z¹ that features four unpaired electrons ready for sp³ hybridization. 3) Common mistake: Confusing the stable ground-state electron configuration with the promoted electron arrangement found in the excited state.

A student might mistakenly lean toward option A or C because they see an oxide reacting with both acids and bases and mistakenly assume it must be purely alkaline or acidic. However, amphoteric oxides like Al2O3 and ZnO have the unique dual capability of exhibiting both acid-base behaviors. When placed in water they remain insoluble, yet they readily dissolve when exposed to acids such as HCl to produce salts and water, as well as bases like NaOH to form complex salts such as Na2ZnO2. Common mistake: Confusing amphoteric behavior with neutral or single-character oxides.