A-Level Chemistry Practice Test 4
60 original multiple-choice questions with answers & explanations — covering the full A-Level Chemistry syllabus (AQA, Edexcel & OCR), AS & A2.
Note: These are original practice questions written in A-Level multiple-choice style — not reproduced exam questions. Use them to test your readiness for the real A-Level Chemistry exams.
📱 How to use: Try each question first, then click “Show Answer” to check. Covers the full A-Level course: atomic structure, amount of substance, bonding, energetics & thermodynamics, kinetics, equilibria, redox & electrode potentials, acids & buffers, inorganic chemistry, and organic chemistry with spectroscopy.
⚛ Atomic Structure & Periodicity
Q1Silicon has three isotopes: 28Si (92.0% abundance), 29Si (5.0% abundance) and 30Si (3.0% abundance). What is the relative atomic mass of silicon?
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Correct: (C)
Ar = (0.920 × 28) + (0.050 × 29) + (0.030 × 30) = 25.76 + 1.45 + 0.90 = 28.1
Q2The successive ionisation energies of an element are 580, 1820, 2740 and 11600 kJ mol^-1. To which group of the Periodic Table does the element belong?
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Correct: (A)
There is a very large jump between the 3rd and 4th ionisation energies, showing that the 4th electron is removed from an inner shell; the element therefore has 3 electrons in its outer shell.
Q3What is the ground-state electronic configuration of a chromium atom?
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Correct: (D)
Chromium is an exception to the expected filling order: a half-filled 3d subshell is particularly stable, so the configuration is [Ar] 3d5 4s1.
Q4In a time of flight mass spectrometer, all the ions are accelerated so that they have the same kinetic energy. Which ion has the shortest time of flight?
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Correct: (B)
With the same kinetic energy, the lightest ion travels fastest (v = sqrt(2KE/m)), so the ion with the smallest m/z value has the shortest flight time.
Q5Why is the first ionisation energy of aluminium lower than that of magnesium?
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Correct: (A)
The 3p electron in Al is further from the nucleus and shielded by the 3s electrons, so it is removed more easily despite the greater nuclear charge.
⚖ Amount of Substance
Q6A 0.500 dm^3 sample of a gas with Mr = 44 is held at 200 kPa and 293 K. What is the mass of the gas? (R = 8.31 J K^-1 mol^-1)
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Correct: (C)
n = pV / RT = (200000 × 5.00 × 10^-4) / (8.31 × 293) = 100 / 2435 = 0.0411 mol. Mass = 0.0411 × 44 = 1.81 g.
Q7A 25.0 cm^3 sample of sodium carbonate solution reacts exactly with 22.5 cm^3 of 0.200 mol dm^-3 hydrochloric acid. The equation is Na2CO3 + 2HCl → 2NaCl + H2O + CO2. What is the concentration of the sodium carbonate solution?
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Correct: (D)
Moles of HCl = 0.200 × 22.5 / 1000 = 4.50 × 10^-3 mol, so moles of Na2CO3 = 2.25 × 10^-3 mol. Concentration = 2.25 × 10^-3 / (25.0 / 1000) = 0.0900 mol dm^-3.
Q8The theoretical yield of a synthesis is 10.7 g, but only 8.00 g of pure product is isolated. What is the percentage yield?
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Correct: (B)
Percentage yield = (8.00 / 10.7) × 100 = 75%.
Q9Complete combustion of 0.300 g of a compound containing only carbon, hydrogen and oxygen produces 0.440 g of CO2 and 0.180 g of H2O. What is the empirical formula of the compound?
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Correct: (A)
Moles of C = 0.440 / 44 = 0.0100 (mass 0.120 g). Moles of H = 2 × (0.180 / 18) = 0.0200 (mass 0.020 g). Mass of O = 0.300 – 0.120 – 0.020 = 0.160 g = 0.0100 mol. Ratio C : H : O = 1 : 2 : 1, so the empirical formula is CH2O.
Q10How many molecules are there in 0.880 g of carbon dioxide? (Mr of CO2 = 44; Avogadro constant = 6.02 × 10^23 mol^-1)
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Correct: (C)
Moles of CO2 = 0.880 / 44 = 0.0200 mol. Number of molecules = 0.0200 × 6.02 × 10^23 = 1.20 × 10^22.
Q11Which reaction has an atom economy of 100%?
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Correct: (B)
This is an addition reaction with only one product, so all the atoms in the reactants end up in the desired product.
🔗 Bonding & Structure
Q12What is the shape of a PCl5 molecule?
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Correct: (D)
Phosphorus has 5 bonding pairs and no lone pairs, giving a trigonal bipyramidal shape with bond angles of 90° and 120°.
Q13For magnesium chloride: enthalpy of formation = -641 kJ mol^-1; enthalpy of atomisation of Mg = +150 kJ mol^-1; first + second ionisation energies of Mg = +2189 kJ mol^-1; enthalpy of atomisation of chlorine = +121 kJ mol^-1 per mole of Cl atoms; electron affinity of Cl = -349 kJ mol^-1. What is the lattice enthalpy of MgCl2?
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Correct: (A)
Born-Haber cycle: -641 = 150 + 2189 + 2(121) + 2(-349) + lattice enthalpy = 1883 + lattice enthalpy, so lattice enthalpy = -641 – 1883 = -2524 kJ mol^-1.
Q14Which compound has the highest boiling point?
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Correct: (C)
Ethanol forms hydrogen bonds between its molecules, giving it a much higher boiling point (78 °C) than the similarly-sized compounds held together only by van der Waals forces.
Q15Why is the lattice enthalpy of NaF more exothermic than that of NaCl?
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Correct: (B)
Both compounds contain singly charged ions, but the smaller fluoride ion allows a shorter internuclear distance in the lattice, so the attraction is stronger and more energy is released.
Q16Graphite conducts electricity along its layers because
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Correct: (D)
The fourth outer electron of each carbon atom is delocalised within the layer and can move along it, carrying the charge.
Q17Which compound forms hydrogen bonds between its molecules?
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Correct: (A)
Hydrogen bonding occurs when H is bonded to a very electronegative atom (N, O or F); ammonia qualifies, but in H2S and PH3 the electronegativity difference is too small.
🔥 Energetics & Thermodynamics
Q18When 0.0100 mol of ethanol is burned completely, the heat released raises the temperature of 100 g of water by 20.0 K. The specific heat capacity of water is 4.18 J g^-1 K^-1. What is the experimental enthalpy of combustion of ethanol?
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Correct: (C)
q = mcΔT = 100 × 4.18 × 20.0 = 8360 J. ΔH = -8360 / 0.0100 = -836000 J mol^-1 = -836 kJ mol^-1 (less exothermic than the data-book value because of heat losses).
Q19Standard enthalpies of combustion: C = -394 kJ mol^-1, H2 = -286 kJ mol^-1, CH4 = -890 kJ mol^-1. What is the standard enthalpy of formation of methane?
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Correct: (B)
For C + 2H2 → CH4: ΔHf = [ΔHc(C) + 2 ΔHc(H2)] – ΔHc(CH4) = (-394 – 572) – (-890) = -966 + 890 = -76 kJ mol^-1.
Q20Ammonium nitrate dissolves in water in an endothermic process, yet the dissolving happens spontaneously at room temperature. This shows that
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Correct: (D)
The ions become much more disordered when the solid dissolves, so ΔS is positive and TΔS outweighs the positive ΔH in ΔG = ΔH – TΔS.
Q21A reaction has ΔH = -100 kJ mol^-1 and ΔS = -200 J K^-1 mol^-1. What is the value of ΔG for this reaction at 298 K?
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Correct: (A)
ΔG = ΔH – TΔS = -100 – 298(-0.200) = -100 + 59.6 = -40.4 kJ mol^-1, so the reaction is feasible at this temperature.
Q22The lattice enthalpy (for the dissociation of the lattice into gaseous ions) of KCl is +701 kJ mol^-1. The enthalpies of hydration are K^+ = -322 kJ mol^-1 and Cl^- = -364 kJ mol^-1. What is the enthalpy of solution of KCl?
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Correct: (C)
ΔH solution = lattice dissociation + hydration of ions = 701 + (-322) + (-364) = +15 kJ mol^-1.
Q23Bond enthalpies: C=C = 612, H-H = 436, C-C = 348, C-H = 412 kJ mol^-1. What is the enthalpy change for the reaction C2H4 + H2 → C2H6?
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Correct: (B)
Bonds broken: C=C and H-H = 612 + 436 = 1048 kJ mol^-1. Bonds formed: C-C and 2 C-H = 348 + 2(412) = 1172 kJ mol^-1. ΔH = 1048 – 1172 = -124 kJ mol^-1.
⏱ Kinetics & Rate Equations
Q24Initial rate experiments show that doubling [A] increases the rate by a factor of 4, while doubling [B] has no effect on the rate. What is the rate equation for the reaction?
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Correct: (D)
The reaction is second order in A and zero order in B, so B does not appear in the rate equation: rate = k[A]^2.
Q25What are the units of the rate constant for a third-order reaction?
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Correct: (A)
Rate (mol dm^-3 s^-1) = k[A]^3, so k has units mol dm^-3 s^-1 / (mol dm^-3)^3 = mol^-2 dm^6 s^-1.
Q26A first-order reaction has a half-life of 600 s. What is the value of the rate constant?
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Correct: (C)
For a first-order reaction, k = ln 2 / t1/2 = 0.693 / 600 = 1.16 × 10^-3 s^-1.
Q27A reaction has an activation energy of 50.0 kJ mol^-1. Its rate constant at 300 K is 2.00 × 10^-3 s^-1. What is the rate constant at 320 K? (R = 8.31 J K^-1 mol^-1)
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Correct: (B)
ln(k2/k1) = -Ea/R (1/T2 – 1/T1) = -(50000/8.31)(1/320 – 1/300) = -6017 × (-2.083 × 10^-4) = 1.254. k2/k1 = e^1.254 = 3.50, so k2 = 3.50 × 2.00 × 10^-3 = 7.0 × 10^-3 s^-1.
Q28A catalyst increases the rate of a reaction because it
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Correct: (D)
A catalyst is not used up and does not change particle energies or equilibrium positions; it lowers the activation energy so more collisions exceed it.
⚖ Chemical Equilibria (Kc & Kp)
Q29At equilibrium for the reaction H2(g) + I2(g) ⇌ 2HI(g), the concentrations are [H2] = 0.10 mol dm^-3, [I2] = 0.10 mol dm^-3 and [HI] = 0.80 mol dm^-3. What is the value of Kc?
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Correct: (A)
Kc = [HI]^2 / ([H2][I2]) = 0.80^2 / (0.10 × 0.10) = 0.64 / 0.010 = 64 (no units).
Q30In the Haber process equilibrium N2(g) + 3H2(g) ⇌ 2NH3(g), the equilibrium partial pressures are N2 = 20 kPa, H2 = 60 kPa and NH3 = 20 kPa. What is the value of Kp?
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Correct: (C)
Kp = (pNH3)^2 / (pN2 × (pH2)^3) = 20^2 / (20 × 60^3) = 400 / 4.32 × 10^6 = 9.26 × 10^-5 kPa^-2.
Q31A catalyst is added to a reaction mixture that has already reached equilibrium. What happens?
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Correct: (B)
A catalyst speeds up the forward and reverse reactions equally, so equilibrium is reached faster but its position and Kc are unchanged.
Q32In the equilibrium PCl5(g) ⇌ PCl3(g) + Cl2(g), the equilibrium concentrations are [PCl5] = 1.20 mol dm^-3, [PCl3] = 0.80 mol dm^-3 and [Cl2] = 0.80 mol dm^-3. What is the value of Kc?
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Correct: (D)
Kc = (0.80 × 0.80) / 1.20 = 0.64 / 1.20 = 0.533 mol dm^-3.
Q33At equilibrium in the esterification CH3COOH + C2H5OH ⇌ CH3COOC2H5 + H2O, a mixture contains 0.20 mol of ethanoic acid, 0.20 mol of ethanol, 0.80 mol of ethyl ethanoate and 0.80 mol of water, all in the same volume. What is the value of Kc?
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Correct: (A)
Kc = (0.80 × 0.80) / (0.20 × 0.20) = 0.64 / 0.040 = 16 (no units, as the volumes cancel).
🔋 Redox & Electrode Potentials
Q34What is the average oxidation state of sulfur in Na2S2O3?
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Correct: (C)
2(+1) + 2x + 3(-2) = 0, so 2x = +4 and x = +2 (the two sulfur atoms are actually in different oxidation states, but the average is +2).
Q35E° values: Mg^2+/Mg = -2.37 V; Ag^+/Ag = +0.80 V. What is the standard cell potential of a cell combining these two half-cells?
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Correct: (B)
E°cell = E°(more positive) – E°(more negative) = 0.80 – (-2.37) = +3.17 V.
Q36Standard electrode potentials: Cu^2+/Cu = +0.34 V; Fe^2+/Fe = -0.44 V; Zn^2+/Zn = -0.76 V; Mg^2+/Mg = -2.37 V. Which metal is the strongest reducing agent?
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Correct: (D)
The strongest reducing agent is the metal in the half-equation with the most negative E° value, which is Mg (-2.37 V).
Q37E°(Cu^+/Cu) = +0.52 V and E°(Cu^2+/Cu^+) = +0.15 V. What happens when Cu^+ ions are in aqueous solution?
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Correct: (A)
For 2Cu^+ → Cu + Cu^2+, E°cell = 0.52 – 0.15 = +0.37 V, which is positive, so Cu^+ disproportionates.
Q38A current of 0.50 A is passed for 30 minutes through silver nitrate solution. What mass of silver is deposited at the cathode? (F = 96500 C mol^-1; Ar of Ag = 108)
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Correct: (C)
Q = It = 0.50 × 1800 = 900 C, which is 900 / 96500 = 9.33 × 10^-3 mol of electrons. Ag^+ + e^- → Ag, so mass of Ag = 9.33 × 10^-3 × 108 = 1.01 g.
🧫 Acids, Bases & Buffers
Q39What is the pH of a 0.0500 mol dm^-3 solution of propanoic acid? (Ka = 1.3 × 10^-5 mol dm^-3)
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Correct: (B)
[H^+] = sqrt(Ka × c) = sqrt(1.3 × 10^-5 × 0.0500) = sqrt(6.5 × 10^-7) = 8.06 × 10^-4 mol dm^-3. pH = -log(8.06 × 10^-4) = 3.09.
Q40Equal volumes (25.0 cm^3) of 0.100 mol dm^-3 hydrochloric acid and 0.0500 mol dm^-3 sodium hydroxide solution are mixed. What is the pH of the resulting solution?
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Correct: (D)
Moles of H^+ = 2.50 × 10^-3; moles of OH^- = 1.25 × 10^-3. Excess H^+ = 1.25 × 10^-3 mol in 50.0 cm^3, so [H^+] = 0.0250 mol dm^-3 and pH = -log(0.0250) = 1.60.
Q41A buffer solution is made by mixing 0.300 mol of ethanoic acid with 0.200 mol of sodium ethanoate in the same volume of solution. The pKa of ethanoic acid is 4.76. What is the pH of the buffer?
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Correct: (A)
pH = pKa + log([salt] / [acid]) = 4.76 + log(0.200 / 0.300) = 4.76 – 0.18 = 4.58.
Q42At 50 °C, the ionic product of water, Kw, is 5.5 × 10^-14 mol^2 dm^-6. What is the pH of pure water at this temperature?
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Correct: (C)
pKw = -log(5.5 × 10^-14) = 13.26. In pure water [H^+] = [OH^-], so pH = pKw / 2 = 6.63. The water is still neutral, even though the pH is below 7.
Q43Which salt forms an acidic solution when dissolved in water?
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Correct: (B)
NH4Cl contains the conjugate acid of a weak base (NH4^+) and the conjugate base of a strong acid (Cl^-), so its solution is acidic. Sodium ethanoate and sodium carbonate give alkaline solutions, and KNO3 is neutral.
⚗ Inorganic Chemistry
Q44Which Group 2 carbonate is the most stable to thermal decomposition?
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Correct: (D)
The carbonates become more thermally stable down Group 2 because the larger cation has a lower charge density and polarises (distorts) the carbonate ion less.
Q45Concentrated sulfuric acid is added to solid sodium bromide and the mixture is warmed. What is observed?
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Correct: (A)
Bromide ions are strong enough reducing agents to reduce the sulfuric acid, so Br^- is oxidised to orange Br2 vapour (and SO2 is also formed); chloride ions cannot do this and give only HCl.
Q46Zinc is added to acidified potassium dichromate(VI) solution and the mixture is shaken. What colour change is seen?
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Correct: (C)
Zinc reduces orange Cr2O7^2- ions (Cr +6) to green Cr^3+ ions; with excess zinc the reduction can continue to blue Cr^2+.
Q47Which ligand is bidentate?
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Correct: (B)
The ethanedioate ion has two oxygen atoms that can each form a coordinate bond to the central metal ion; NH3, Cl^- and H2O are monodentate.
Q48A solution is warmed with sodium hydroxide solution and a gas is produced that turns damp red litmus paper blue. Which ion was present in the solution?
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Correct: (D)
Ammonium ions react with warm alkali to release ammonia gas: NH4^+ + OH^- → NH3 + H2O, and ammonia is alkaline.
🛢 Organic Chemistry I
Q49Which pair of products could be formed when decane, C10H22, is cracked?
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Correct: (A)
The products must contain 10 C atoms and 22 H atoms in total: C8H18 + C2H4 gives C = 10 and H = 22. The other pairs give 24 H atoms, so they are impossible.
Q50The hydrolysis of 2-bromo-2-methylpropane by aqueous alkali is first order in the halogenoalkane and zero order in hydroxide ions. This is because
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Correct: (C)
This is the SN1 mechanism: the slow first step forms a tertiary carbocation, which is stabilised by three alkyl groups, and the nucleophile attacks it rapidly in the second step.
Q51Which species can act as a nucleophile?
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Correct: (B)
A nucleophile donates a lone pair of electrons to form a bond; ammonia has a lone pair on nitrogen. H^+, BF3 and NO2^+ are electrophiles (electron-pair acceptors).
Q52Which alkene shows cis-trans (E/Z) isomerism?
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Correct: (D)
Each carbon of the C=C bond in but-2-ene is bonded to two different groups (H and CH3), so E/Z isomers exist. In the other alkenes, at least one double-bond carbon has two identical groups.
Q53Propan-1-ol is distilled with acidified potassium dichromate(VI) as it forms. What is the organic product collected?
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Correct: (A)
A primary alcohol is oxidised first to an aldehyde; distilling the propanal off as it forms prevents further oxidation to propanoic acid.
Q54Butan-2-ol is dehydrated by heating with concentrated sulfuric acid. Counting E/Z isomers as separate products, how many different alkenes are formed?
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Correct: (C)
The products are but-1-ene, (E)-but-2-ene and (Z)-but-2-ene: three different alkenes.
🔬 Organic Chemistry II & Analysis
Q55Which compound forms a silver mirror when warmed with Tollens' reagent?
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Correct: (B)
Aldehydes are oxidised by Tollens' reagent to carboxylic acids while Ag^+ ions are reduced to silver metal; ketones, alcohols and carboxylic acids do not react.
Q56Propanoic acid is warmed with methanol in the presence of a concentrated sulfuric acid catalyst. What is the main organic product?
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Correct: (D)
In esterification the alcohol provides the first part of the ester name and the acid the second: methanol + propanoic acid gives methyl propanoate and water.
Q57What are the correct reagents and conditions for the bromination of benzene?
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Correct: (A)
Benzene undergoes electrophilic substitution, not addition, so a halogen carrier catalyst (FeBr3) is needed to polarise the Br-Br bond and generate the electrophile.
Q58Propanenitrile is reduced using hydrogen and a nickel catalyst. What is the product?
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Correct: (C)
Reduction of a nitrile adds hydrogen across the C≡N bond: CH3CH2C≡N + 2H2 → CH3CH2CH2NH2, propylamine.
Q59In a strongly acidic solution, glycine (aminoethanoic acid) exists mainly as
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Correct: (B)
At low pH the -COO^- group of the zwitterion accepts a proton, so the species present is +NH3-CH2-COOH, which has an overall positive charge.
Q60How many peaks are there in the carbon-13 NMR spectrum of benzene?
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Correct: (D)
All six carbon atoms in benzene are in identical environments because of the delocalised ring, so there is only one peak.
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