All 50 questions from the Joint Admissions and Matriculation Board (JAMB) Biology 2015 Objective paper, with the correct answer and a full explanation for each. Free, no signup needed.
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Pollution of water by crude oil can lead to
Crude oil is a major pollutant of water; it blocks oxygen exchange at the surface, leading to a decrease in the oxygen content of the water.
When a few drops of barium chloride is added to an unknown sample acidified with hydrochloric acid, a white precipitate insoluble in excess of the acid was obtained. The likely anion in the sample is
A white precipitate that remains undisclosed (insoluble) even after adding excess HCl confirms the presence of SO₄²⁻, since CO₃²⁻ and SO₃²⁻ would dissolve with effervescence.
Oxygen in air can be removed using
Alkaline pyrogallol solution is commonly used to absorb/remove oxygen from air in gas analysis.
Calculate the pH of a solution of 0.0001moldm⁻³ hydrochloric acid.
[H⁺] = 0.0001 = 10⁻⁴ moldm⁻³. pH = −log₁₀(10⁻⁴) = 4.
Which of the following drying agents is NOT suitable for drying hydrogen sulphide?
CaO (a basic drying agent) would react with the acidic gas H₂S, so it is unsuitable for drying it.
Diamond is used in making jewelry due to its
Diamond's high refractive index makes it shine brilliantly when polished, making it a good ornament.
The presence of impurities in a solid will make the melting point to
Impurities generally cause the melting point of a solid to decrease (melting point depression), while they raise the boiling point of a liquid.
The discovery that protons and neutrons are concentrated at the nucleus of an atom was postulated by
Rutherford's gold-foil experiment led to the discovery that the mass/protons and neutrons of an atom are concentrated in a small dense nucleus.
Which of the following is a hydroscopic substance?
Hygroscopic substances absorb moisture from the atmosphere; NaNO₃ is a common example, alongside CuO and H₂SO₄.
In a chemical reaction, when the energy of the colliding reactant particles is less than the activation energy, the reaction will
For a reaction to occur, colliding particles must have energy greater than or equal to the activation energy; if less, the reaction will not occur.
The monomer of natural rubber is
Natural rubber is a polymer of the diolefin monomer 2-methylbuta-1,3-diene (isoprene).
The monomer of natural rubber is
As with question 11, the monomer of natural rubber is 2-methylbuta-1,3-diene (this question is repeated in the original source).
PCl₅(g) ⇌ PCl₃(g) + Cl₂(g), ΔH = +ve. In the reaction above, the forward reaction is favoured by
Since the forward reaction is endothermic (ΔH = +ve), it is favoured by an increase in temperature.
Which of the following halogens is the most reactive?
Fluorine is the most electronegative element and the most reactive halogen; reactivity decreases down the group: F > Cl > Br > I.
A gas that forms a black precipitate with lead(II) ethanoate is
H₂S reacts with lead(II) ethanoate to produce lead(II) sulphide, an insoluble black precipitate.
The common ore of iron is
Magnetite is a common ore of iron; galena is an ore of lead, cassiterite an ore of tin, and bauxite an ore of aluminium.
A property common to the two structures shown (normal pentane and 2-methylbutane) is that they have the same
Normal pentane and 2-methylbutane are isomers — they share the same molecular formula (C₅H₁₂) but have different structural formulae.
The type of salt that ionizes to produce three different ions in solution is
A double salt ionizes to produce three different ions in solution — two metallic ions and a negative acid radical, or a metallic ion, an ammonium ion, and a negative acid radical (e.g. potash alum).
H₂S(g) + Br₂(g) → 2HBr(g) + S(s). In the reaction above, the oxidizing agent is
The oxidation number of bromine decreases from 0 in Br₂ to −1 in HBr (reduction), so Br₂ is the oxidizing agent, while H₂S is the reducing agent.
The process whereby a gaseous body loses some of its kinetic energy to a colder body is referred to as
When a gaseous substance loses kinetic energy, it may change into liquid form; this process is known as condensation.
Which of the quantum numbers determines the energy sub-level in an orbital?
The azimuthal (angular/secondary/subsidiary) quantum number determines the energy sub-level in an orbital.
Fehling's solution can be used to distinguish between
Alkanals (e.g. CH₃CHO, ethanal) reduce Fehling's solution while alkanones (e.g. CH₃COCH₃, propanone) do not, so Fehling's test distinguishes them.
What is the molecular formula of a compound with empirical formula CH₂ and vapour density 42? [C=12, H=1]
Molar mass = 2×vapour density = 84. Empirical formula mass (CH₂) = 14. n = 84/14 = 6, so molecular formula = C₆H₁₂.
The separation technique that is based on the principle of solubility of a solid in two miscible liquids is
Fractional/solvent extraction (precipitation as listed) exploits differing solubility of a solid in two miscible liquids to separate it.
Hydrogen bond can be found in
Hydrogen bonding occurs in compounds containing hydrogen bonded to a very small, highly electronegative element such as fluorine; hydrogen fluoride exhibits hydrogen bonding.
24g of magnesium reacts with dilute hydrochloric acid. Calculate the volume of hydrogen gas evolved at s.t.p. [Mg=24, Molar volume of gas at s.t.p. = 22.4dm³]
Moles of Mg = 24/24 = 1 mol. Mg + 2HCl → MgCl₂ + H₂, so 1 mol Mg produces 1 mol H₂ = 22.4dm³ at s.t.p.
Aluminium is usually used as electrical cables due to its
Aluminium's good electrical conductivity is why it is used for electrical cables.
A chemical reaction with entropy change of +20 Jk⁻¹ and free energy change +55000J occurred at −23°C. Calculate the enthalpy change.
ΔG = ΔH − TΔS ⟹ ΔH = ΔG + TΔS = 55000 + (250×20) = 55000+5000 = 60000J.
The enzyme invertase converts sucrose into
Invertase hydrolyses sucrose into glucose and fructose.
The number of lone pairs of electrons in a water molecule is
The oxygen atom in a water molecule has two lone pairs of electrons.
n monosaccharide (−x→) polysaccharide (−y→) + n water. In the illustration above, x and y respectively represent
The conversion of monosaccharide to polysaccharide is condensation (with loss of water); the reverse process (polysaccharide back to monosaccharide) is hydrolysis.
The main product of the reaction between phosphorus(V) chloride and ethanol is
Phosphorus(V) chloride reacts with ethanol (C₂H₅OH + PCl₅ → C₂H₅Cl + POCl₃ + HCl) to give chloroethane as the main organic product.
The bond-breaking energies in an endothermic reaction is usually
In an endothermic reaction, the bond-breaking energy is usually more than the bond-forming energy (the reverse is true for exothermic reactions).
²³⁴₉₀Th → ˣ_yPa + β. In the reaction above, x and y respectively are
Beta decay: mass number is conserved (x=234) while atomic number increases by 1 (y=91).
The compound of calcium used to make refractory furnace linings is
Calcium oxide (quicklime), due to its extremely high melting point (about 2600°C), is used for making refractory furnace linings.
The mass of copper deposited when a current of 2.0A is passed through a solution of a copper salt for 60 minutes is [Cu=64, F=96500 Cmol⁻¹]
Q=It=2×3600=7200C. For 1 mole Cu (64g), 2F (193000C) is required, so mass deposited = (64/193000)×7200 ≈ 2.39g.
Which of the following compounds will liberate carbon(IV) oxide on reacting with sodium trioxocarbonate(IV)?
Acids (like ethanoic acid, CH₃COOH) react with carbonates to liberate carbon(IV) oxide.
Kerosene is a petroleum fraction that distils over in the temperature range of
Kerosene is a mixture of hydrocarbons containing C₁₀–C₁₆ carbon atoms, boiling between 200°C and 250°C.
The preference in the usage of asbestos support to platinum block as a catalyst can be attributed to its
A catalyst's effectiveness is higher with increased surface area; asbestos support provides this over a plain platinum block.
In the deduction of ethyl ethanoate with LiAlH₄, the product obtained is
Ethyl ethanoate is reduced to ethanol using reducing agents like lithium aluminium hydride (LiAlH₄).
A sample of a salt was heated on a Bunsen flame. If the colour of the flame turned bluish-green, the metal present is likely to be
Copper produces a bluish-green flame colouration in a flame test.
A salt that loses moisture on exposure to the atmosphere is said to be
A salt that loses its water of crystallization to become anhydrous on exposure to the atmosphere is said to be efflorescent.
In the graph, at what temperature is the solubility of KHCO₃ and NaCl the same?
KHCO₃ and NaCl have the same solubility at the point where their solubility curves intersect, which corresponds to about 42°C.
1050cm³ of helium gas was produced at −33°C and 700mmHg. What volume would the gas occupy at 23°C and 750mmHg?
Using the combined gas law: V₂ = P₁V₁T₂/(P₂T₁) = (700×1050×296)/(750×240) ≈ 1208.67cm³.
¹⁴₇N + X → ¹⁷₈O + ¹₁H. In the reaction above, X is a(n)
Balancing mass and atomic numbers (14+4=17+1; 7+2=8+1) shows X is a helium atom (alpha particle).
The colour of phenolphthalein in an alkaline medium is
Phenolphthalein is colourless in acidic/neutral medium but turns pink/red in alkaline medium.
Calculate the molecular formula of a compound with empirical formula CH₂O and relative molecular mass 120. [C=12, O=16, H=1]
Empirical formula mass = 12+2+16 = 30. n = 120/30 = 4, so molecular formula = (CH₂O)₄ = C₄H₈O₄.
MnO₂(s) + 4HCl(aq) → MnCl₂(aq) + Cl₂(g) + 2H₂O(l). In the reaction above, MnO₂ acts as a(n)
The oxidation state of manganese decreases from +4 in MnO₂ to +2 in MnCl₂ (reduction), so MnO₂ is the oxidizing agent.
Calculate the mass of magnesium that would be deposited by 8 faradays of electricity. [Mg=24]
Mg²⁺ + 2e⁻ → Mg, so 2F deposits 1 mole of Mg (24g). 8F will deposit 4 moles = 96g.
Which of the following hydrocarbons will NOT undergo polymerization reaction?
C₄H₁₀ (butane) is an alkane (saturated hydrocarbon); alkanes do not undergo polymerization reactions.
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