IB Chemistry Practice Test 11

Correct: (A)

The number of molecules is proportional to the amount in moles, and 2.0 mol is the largest amount listed.

Correct: (B)

Mole ratio C:H:O = 40.0/12.0 : 6.7/1.0 : 53.3/16.0 = 3.33 : 6.70 : 3.33 = 1 : 2 : 1, giving CH2O.

Correct: (C)

V = nRT/p = (0.250 x 8.31 x 300)/100000 = 0.00623 m^3 = 6.23 dm^3.

Correct: (D)

n(NaCl) = 5.85/58.5 = 0.100 mol; c = 0.100/0.500 = 0.200 mol dm^-3.

Correct: (B)

Chromium is an exception to the expected filling pattern; a half-filled 3d subshell gives [Ar] 4s^1 3d^5.

Correct: (C)

Ar = (90.0 x 20 + 10.0 x 21)/100 = (1800 + 210)/100 = 20.1.

Correct: (D)

Each MgCl2 unit gives 3 ions, so ions = 0.50 x 3 x 6.02 x 10^23 = 9.03 x 10^23.

Correct: (A)

At constant volume, p is proportional to T in kelvin, so doubling T doubles p.

Correct: (C)

18 g of H2O is 1.0 mol of water molecules, and each molecule contains 2 H atoms, giving 2.0 mol of H atoms.

Correct: (D)

Percentage yield = (18.0/24.0) x 100 = 75.0%.

Correct: (A)

NH3 has three bonding pairs and one lone pair, so the molecular geometry is trigonal pyramidal.

Correct: (B)

Ethanol contains an O-H group, so molecules form hydrogen bonds with each other.

Correct: (D)

MgCl2 consists of Mg^2+ and Cl^- ions held together by electrostatic attraction.

Correct: (A)

CO2 has O=C=O, and each oxygen atom has two non-bonding pairs.

Correct: (B)

Four bonding pairs arrange tetrahedrally, giving bond angles of about 109.5°.

Correct: (C)

CHCl3 is not symmetrical because one substituent is H and three are Cl, so the bond dipoles do not cancel.

Correct: (A)

In graphite each carbon is bonded to three others in layers, and the layers are held by weak intermolecular forces.

Correct: (C)

Sodium chloride is an ionic lattice, so strong attractions between oppositely charged ions must be overcome on melting.

Correct: (B)

Each carbon in ethene has three electron domains in a trigonal planar arrangement, corresponding to sp^2 hybridization.

Correct: (D)

Bronze is an alloy of metals, with positive metal ions in a sea of delocalized electrons.

Correct: (B)

Across a period the nuclear charge increases while electrons are added to the same shell, pulling the electrons closer.

Correct: (D)

The atom has 26 electrons, so it is iron, Fe.

Correct: (A)

CH3COOH contains the -COOH group, which is the carboxylic acid functional group.

Correct: (C)

Successive members of a homologous series differ by a CH2 unit.

Correct: (C)

Acyclic alkenes have general formula CnH2n; for n = 5 this is C5H10.

Correct: (A)

Across a period, greater nuclear charge and smaller radius make the outer electron harder to remove.

Correct: (D)

Partially filled d orbitals can split in energy, and electrons absorb visible light when moving between them.

Correct: (B)

CH3COOCH3 contains the -COO- linkage characteristic of an ester.

Correct: (D)

Exothermic reactions release heat to the surroundings, so the enthalpy of the products is lower.

Correct: (B)

q = mcΔT = 100 x 4.18 x 5.00 = 2090 J = 2.09 kJ.

Correct: (C)

Bonds broken = 436 + 242 = 678 kJ mol^-1; bonds formed = 2 x 431 = 862 kJ mol^-1; ΔH = 678 – 862 = -184 kJ mol^-1.

Correct: (A)

Standard combustion refers to complete burning of 1 mol of substance in oxygen under standard conditions.

Correct: (A)

Lattice formation enthalpy is for gaseous ions combining to form 1 mol of the ionic solid.

Correct: (D)

Dissolving a solid to form mobile aqueous ions increases the disorder of the system.

Correct: (B)

A negative Gibbs energy change indicates a spontaneous process under the stated conditions.

Correct: (C)

ΔH = [-394 + 2(-286)] – [-75] = -966 + 75 = -891 kJ mol^-1, approximately -890 kJ mol^-1.

Correct: (B)

Rate measures how concentration changes with time.

Correct: (A)

At higher temperature more molecules have higher energies, so the peak moves right and flattens while total area stays constant.

Correct: (D)

A catalyst works by lowering the activation energy through a different mechanism.

Correct: (C)

The reaction is first order in A and second order in B, so rate = k[A][B]^2.

Correct: (C)

First-order half-life depends only on k, not on the starting concentration.

Correct: (B)

Products are placed over reactants, each raised to its stoichiometric coefficient.

Correct: (A)

Higher pressure favours the side with fewer gas molecules; N2O4 has 1 mol of gas compared with 2 mol for NO2.

Correct: (D)

When Q > K there is too much product relative to equilibrium, so the net change is towards reactants.

Correct: (D)

For rate = k[A]^2, k = rate/[A]^2, giving dm^3 mol^-1 s^-1.

Correct: (C)

60 minutes is three half-lives, so the fraction remaining is (1/2)^3 = 1/8.

Correct: (B)

Equilibrium is dynamic because both reactions continue at equal rates.

Correct: (A)

A catalyst speeds both directions equally, so the equilibrium position and Kc do not change.

Correct: (A)

HCl is a strong acid, so [H^+] = 0.010 mol dm^-3 and pH = -log(0.010) = 2.00.

Correct: (D)

Removing one H^+ from HCO3^- gives CO3^2-.

Correct: (C)

A buffer contains significant amounts of a weak acid and its conjugate base.

Correct: (B)

If sulfur is x, x + 4(-2) = -2, so x = +6.

Correct: (B)

Cu^2+ ions are reduced at the cathode to form copper metal.

Correct: (C)

A very negative electrode potential means the metal readily loses electrons, so it is a strong reducing agent.

Correct: (A)

SN2 requires backside attack, so it is fastest for primary, unhindered halogenoalkanes.

Correct: (D)

The electrophile adds to the double bond and the other carbon becomes a carbocation.

Correct: (C)

Controlled oxidation of a primary alcohol gives an aldehyde, which can be removed by distillation before further oxidation.

Correct: (A)

Acid + carbonate → salt + water + carbon dioxide.

Correct: (D)

The conjugate base formed hydrolyses water to produce OH^- ions, so the solution is basic.

Correct: (B)

Oxidation at the anode releases electrons, which travel through the external circuit to the cathode.