IB Chemistry Practice Test 2

Correct: (C)

Iron has atomic number 26, so the number of neutrons = 56 – 26 = 30.

Correct: (D)

The longest wavelength corresponds to the smallest energy change, and the n = 3 → n = 2 drop is the smallest of the transitions listed.

Correct: (A)

Amount of NH3 = 34 / 17 = 2.0 mol, which contains 2.0 mol of N atoms; mass of N = 2.0 × 14 = 28 g.

Correct: (B)

V = nRT / P = (0.25 × 8.31 × 273) / (1.00 × 10^5) = 5.7 × 10^-3 m^3 = 5.7 dm^3.

Correct: (C)

Moles of HCl = 2.00 × 0.0250 = 0.0500 mol; concentration = 0.0500 / 0.250 = 0.200 mol dm^-3.

Correct: (B)

The Mg : H2 ratio in the equation is 1 : 1, so 0.30 mol of H2 is produced.

Correct: (C)

Moles of C = 0.24 / 12 = 0.020 and moles of H = 0.06 / 1 = 0.060; the ratio is 1 : 3, so the empirical formula is CH3.

Correct: (D)

The m/z value of the molecular ion peak corresponds directly to the relative molecular mass, so Mr = 46.

Correct: (A)

A magnesium atom has 12 electrons; forming Mg^2+ removes two, leaving 10 electrons.

Correct: (C)

At constant volume P2 = P1 × T2 / T1 = 100 × (600 / 300) = 200 kPa (temperatures in kelvin).

Correct: (C)

Lattice enthalpy increases with ionic charge and decreases with ionic radius; MgO combines small ions with 2+ and 2- charges, giving the strongest attractions.

Correct: (D)

Carbon forms two C=O double bonds, so there are four bonding pairs (eight bonding electrons) around the central atom.

Correct: (A)

Boron has three bonding pairs and no lone pair, giving a trigonal planar geometry with 120° bond angles.

Correct: (C)

Nitrogen molecules contain a N≡N triple bond; O2 has a double bond and F2 and Cl2 have single bonds.

Correct: (B)

Ethanol has an -OH group and forms intermolecular hydrogen bonds; methoxymethane cannot, so its molecules are held together only by weaker dipole-dipole forces.

Correct: (D)

SiO2 forms a continuous three-dimensional network of covalent bonds; iodine, CO2 and ice are simple molecular substances.

Correct: (B)

In a metal, the outer electrons are delocalised and are attracted to the lattice of positive ions; their mobility explains electrical conductivity.

Correct: (A)

O2 and O3 (ozone) are different structural forms of the element oxygen; the other pairs are isotopes or different compounds.

Correct: (C)

Nitrogen has four electron domains (three bonding pairs and one lone pair), corresponding to sp^3 hybridisation.

Correct: (D)

Water is bent and unsymmetrical, so its bond dipoles do not cancel; CCl4, CH4 and CO2 are symmetrical and nonpolar overall.

Correct: (B)

Down the group the outer electron is in a higher shell, further from the nucleus and more shielded, so it is removed more easily and reactivity increases.

Correct: (C)

Aluminium oxide reacts with both acids and strong bases; Na2O and MgO are basic oxides and SO3 is an acidic oxide.

Correct: (B)

Cu^2+ has a partially filled 3d subshell (d^9) and is blue in solution; Zn^2+ (d^10), Sc^3+ (d^0) and Ti^4+ (d^0) are colourless.

Correct: (C)

Ethanal is an aldehyde and contains the C=O carbonyl group.

Correct: (A)

C3H6 fits the general formula CnH2n of the alkenes; the other three all fit CnH2n+2.

Correct: (B)

The longest continuous chain has three carbon atoms, with a methyl group attached to carbon 2, giving 2-methylpropane.

Correct: (D)

Pentane and 2-methylbutane share the molecular formula C5H12 but have different structural arrangements.

Correct: (C)

The highest-energy electrons occupy d orbitals, so the element (chromium) is a d-block transition metal.

Correct: (A)

ΔH = ΣΔHf(products) – ΣΔHf(reactants) = [2(-394) + 2(-286)] – [52 + 0] = -1360 – 52 = -1412 kJ mol^-1.

Correct: (B)

q = 500 × 4.18 × 11.4 = 23 826 J ≈ 23.8 kJ released per gram; per mole this is 23.8 × 46 ≈ 1100 kJ, so ΔHc ≈ -1100 kJ mol^-1.

Correct: (D)

Applying Hess's law, the formation reaction is the first equation minus the second: ΔHf(CO) = -394 – (-283) = -111 kJ mol^-1.

Correct: (C)

Bonds broken = 946 + 3(436) = 2254 kJ; bonds formed = 6(391) = 2346 kJ; ΔH = 2254 – 2346 = -92 kJ mol^-1.

Correct: (D)

Two moles of gas combine to form one mole of gas, so the system becomes more ordered and ΔS is negative.

Correct: (C)

ΔG = ΔH – TΔS; with both terms positive, ΔG becomes negative only when TΔS is larger than ΔH, which happens at high temperatures.

Correct: (B)

q = 100 × 4.18 × 6.8 = 2842 J; the amount of water formed = 1.00 × 0.0500 = 0.0500 mol, so ΔH = -2842 / 0.0500 ≈ -57 kJ mol^-1.

Correct: (C)

Bond breaking is endothermic, and the enthalpy of a given bond varies slightly between compounds, so tabulated bond enthalpies are average (mean) values.

Correct: (A)

The rate depends on [A]^2 (second order in A) and is independent of [B] (zero order in B).

Correct: (B)

With a lower activation energy, a greater proportion of collisions have E ≥ Ea and are successful.

Correct: (D)

After each half-life half remains, so after three half-lives the fraction remaining is (1/2)^3 = 1/8 = 12.5%.

Correct: (A)

The volume of gas collected at regular time intervals gives a direct measure of how fast the reaction is proceeding.

Correct: (B)

A large Kc means the equilibrium position lies well to the right; Kc gives no information about the rate of the reaction.

Correct: (D)

The product side has fewer moles of gas (2 compared with 3), so increasing the pressure shifts the equilibrium towards the products; Kc is unchanged at constant temperature.

Correct: (A)

At equilibrium [PCl3] = [Cl2] = 0.20 – 0.16 = 0.040 mol dm^-3, so Kc = (0.040 × 0.040) / 0.16 = 0.0016 / 0.16 = 0.010.

Correct: (B)

From k = rate / [A] = (mol dm^-3 s^-1) / (mol dm^-3) = s^-1.

Correct: (D)

Heating favours the endothermic (reverse) direction, so fewer products are present at equilibrium and Kc becomes smaller.

Correct: (C)

A catalyst speeds up the forward and reverse reactions equally, so the composition at equilibrium is unchanged.

Correct: (B)

The rate is determined by the slow (rate-determining) step, which involves two NO2 molecules, so rate = k[NO2]^2.

Correct: (A)

The exponential term gives the proportion of collisions energetic enough to react; A is the frequency factor, which includes collision frequency and orientation.

Correct: (B)

NaOH is a strong base, so [OH^-] = 0.0010 mol dm^-3, pOH = 3.00, and pH = 14.00 – 3.00 = 11.00.

Correct: (A)

A conjugate acid is formed by adding one H^+; adding H^+ to NH3 gives NH4^+.

Correct: (A)

Added H^+ is removed by the conjugate base, and added OH^- is removed by the weak acid, so the pH changes very little.

Correct: (D)

Using K = +1 and O = -2: +1 + x + 4(-2) = 0, so x = +7.

Correct: (C)

Water is oxidised at the anode, releasing oxygen gas; copper is deposited at the cathode.

Correct: (B)

E°cell = E°(reduction) – E°(oxidation couple) = 0.80 – (-0.44) = +1.24 V.

Correct: (A)

The pi bond of the alkene attacks the bromine molecule and both bromine atoms add across the double bond.

Correct: (D)

With excess oxidising agent under reflux, the primary alcohol is fully oxidised past the aldehyde stage to the carboxylic acid, ethanoic acid.

Correct: (A)

Alkaline hydrolysis of an ester gives the carboxylate salt and the alcohol; CH3COOCH3 gives CH3COO^- and CH3OH.

Correct: (D)

The C-I bond is the weakest carbon-halogen bond and I^- is the best leaving group, so reactivity increases in the order F < Cl < Br < I.

Correct: (A)

The electron-withdrawing chlorine atom stabilises the chloroethanoate ion, so chloroethanoic acid is stronger than ethanoic acid; phenol and ethanol are far weaker acids.

Correct: (D)

The NH4^+ ion is the conjugate acid of the weak base ammonia and hydrolyses in water (NH4^+ ⇌ NH3 + H^+), making the solution acidic.