IB Chemistry Practice Test 5

Correct: (A)

4.00 g / 2.02 g mol^-1 is approx. 2.00 mol H2. Each other sample is approx. 1.00 mol.

Correct: (B)

Mole ratio C:H:O = 40.0/12.01 : 6.7/1.01 : 53.3/16.00 = 3.33:6.63:3.33 = 1:2:1.

Correct: (C)

Fe is [Ar] 4s^2 3d^6. The two 4s electrons are removed first when Fe^2+ forms.

Correct: (D)

Volume = 0.250 mol × 22.7 dm^3 mol^-1 = 5.68 dm^3.

Correct: (A)

Amount = 0.0250 × 0.200 = 0.00500 mol. Concentration = 0.00500 / 0.2500 = 0.0200 mol dm^-3.

Correct: (B)

Relative atomic mass = (0.600 × 69) + (0.400 × 71) = 69.8.

Correct: (C)

Each formula unit gives 3 ions, so amount of ions = 3 × 0.500 = 1.50 mol. Number = 1.50 × 6.02 × 10^23 = 9.03 × 10^23.

Correct: (D)

P2/P1 = (T2/T1)(V1/V2) = 2 × 2 = 4.

Correct: (A)

The 0.300 mol H2 requires only 0.150 mol O2, so H2 is limiting and forms 0.300 mol H2O.

Correct: (B)

Percentage yield = (9.60 / 12.0) × 100 = 80.0%.

Correct: (C)

Boron has three bonding domains and no lone pair, giving a trigonal planar geometry.

Correct: (D)

Water molecules form extensive hydrogen bonds through their O-H bonds and lone pairs.

Correct: (A)

Sulfur in SF6 is surrounded by 12 bonding electrons, so its octet is expanded.

Correct: (B)

NH3 has a trigonal pyramidal geometry. Its lone pair compresses the ideal tetrahedral angle to approx. 107°.

Correct: (C)

Silicon dioxide consists of a continuous network of strong covalent bonds.

Correct: (D)

NH4Cl has ionic bonding between NH4^+ and Cl^- and covalent N-H bonds within NH4^+.

Correct: (A)

Graphite has delocalized electrons in its two-dimensional layers, allowing electrical conduction along the layers.

Correct: (B)

Oxygen has two bonding pairs and two lone pairs. The electron geometry is tetrahedral but the molecular geometry is bent.

Correct: (C)

Mg contributes two valence electrons per atom and has a smaller ionic radius than the Group 1 metals listed, giving stronger metallic bonding.

Correct: (D)

CO2 is linear, so its two equal C=O bond dipoles act in opposite directions and cancel.

Correct: (A)

Period 3 oxides change from basic metal oxides through amphoteric Al2O3 to acidic non-metal oxides.

Correct: (B)

Down the group, greater distance and shielding outweigh the increased nuclear charge, so the outer electron is removed more easily.

Correct: (C)

Electron transitions between split d orbitals absorb visible light, producing coloured transition-metal compounds.

Correct: (D)

Ethanoic acid contains the carboxyl group, -COOH.

Correct: (D)

Each successive member of a homologous series has one additional CH2 unit.

Correct: (C)

In propan-2-ol, the carbon bonded to -OH is attached to two other carbon atoms.

Correct: (B)

Acyclic alkenes follow CnH2n. For n = 4, the formula is C4H8.

Correct: (A)

Increased nuclear charge pulls electrons in the same shell closer to the nucleus, reducing atomic radius.

Correct: (B)

Exothermic reactions release energy and have products at lower enthalpy, so ΔH is negative.

Correct: (C)

q = mcΔT = 100.0 × 4.18 × 10.0 = 4180 J = 4.18 kJ.

Correct: (D)

Hess's law: ΔH = (+20) + (-50) = -30 kJ mol^-1.

Correct: (A)

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

Correct: (B)

Liquid molecules become much more dispersed in the gas phase, increasing entropy.

Correct: (C)

ΔG = ΔH – TΔS = -40.0 – 300(-0.100) = -10.0 kJ mol^-1.

Correct: (D)

Standard enthalpy of formation refers to forming one mole of a compound from its elements under standard conditions.

Correct: (A)

The reaction absorbs heat from the solution, so the solution cools and ΔH is positive.

Correct: (C)

The rate is the rate of formation of NH3 divided by its stoichiometric coefficient, 2.

Correct: (D)

No change with [A] means zero order in A. A fourfold rate increase when [B] doubles means second order in B.

Correct: (A)

The number of particles is unchanged, so the area is constant. A larger fraction has higher energy and the peak moves right and becomes lower.

Correct: (B)

A catalyst provides a different reaction pathway with a lower activation energy.

Correct: (D)

t1/2 = ln 2 / k = 0.693 / 0.0693 = 10.0 s.

Correct: (A)

Products are raised to their stoichiometric coefficients and divided by reactants raised to theirs.

Correct: (B)

Increasing temperature favours the endothermic reverse reaction, shifting equilibrium toward N2 and H2.

Correct: (C)

There are 3 mol of gas on the left and 2 mol on the right, so increased pressure shifts equilibrium toward SO3.

Correct: (A)

If Q < K, more products must form until Q reaches K.

Correct: (B)

In dynamic equilibrium, both reactions continue but at equal rates, so macroscopic properties remain constant.

Correct: (C)

Kc = [B] / [A] = 0.400 / 0.200 = 2.00.

Correct: (D)

A catalyst speeds both forward and reverse reactions equally and does not change K or the equilibrium position.

Correct: (D)

HCl is a strong acid, so [H^+] = 0.0100 = 10^-2 and pH = 2.00.

Correct: (A)

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

Correct: (B)

A buffer contains appreciable amounts of a weak acid and its conjugate base, commonly supplied as its salt.

Correct: (C)

Let the sulfur oxidation number be x: x + 4(-2) = -2, so x = +6.

Correct: (A)

Zn changes from oxidation number 0 to +2, so it loses electrons and is oxidized.

Correct: (B)

E°cell = E°cathode – E°anode = 0.34 – (-0.76) = +1.10 V.

Correct: (C)

Na^+ ions gain electrons at the cathode to form sodium metal.

Correct: (D)

OH^- replaces Br, producing ethanol.

Correct: (B)

The conjugate base formed hydrolyses water to produce OH^-, making the equivalence-point solution basic.

Correct: (C)

pH = pKa + log([base]/[acid]) = 4.70 + log(1) = 4.70.

Correct: (D)

Water is oxidized at the anode, producing oxygen gas.

Correct: (A)

The pi bond of the alkene is attacked by an electrophile in the first step of electrophilic addition.