IB Chemistry Practice Test 12

Correct: (D)

Relative atomic mass accounts for both isotopic masses and their relative abundances.

Correct: (C)

n = m/Mr = 11/44 = 0.250 mol.

Correct: (B)

Number of particles = 2.0 x 6.02 x 10^23 = 1.20 x 10^24.

Correct: (A)

At STP (273 K and 100 kPa), one mole of an ideal gas occupies about 22.7 dm^3.

Correct: (A)

Mr(H2O) = 18, so %O = (16/18) x 100 = 88.9%.

Correct: (D)

2.0 mol H2 needs only 1.0 mol O2 and forms 2.0 mol H2O; H2 is limiting.

Correct: (C)

Amount stays constant: n = 2.00 x 0.0250 = 0.0500 mol; c = 0.0500/0.250 = 0.200 mol dm^-3.

Correct: (B)

Magnesium has 12 electrons arranged as 2 in the first shell, 8 in the second and 2 in the third.

Correct: (B)

Only certain photon energies are emitted, showing that electrons occupy discrete energy levels.

Correct: (A)

m = n x Mr = 0.50 x 100 = 50 g.

Correct: (D)

CO2 has two electron domains around carbon arranged opposite each other, giving a linear molecule.

Correct: (C)

Ionic bonds form from electrostatic attraction between cations and anions.

Correct: (C)

CH4 contains only shared-pair covalent bonds; NH4Cl also has ionic attraction between NH4^+ and Cl^-.

Correct: (B)

Each double bond counts as one electron domain, so CO2 has two domains around carbon.

Correct: (A)

Diamond is a giant covalent network, so many strong covalent bonds must be broken to melt it.

Correct: (D)

Sulfur in SF6 is surrounded by 12 electrons, which is an expanded octet.

Correct: (D)

CH4 is non-polar, so only London dispersion forces act between its molecules.

Correct: (A)

In ice, hydrogen bonds hold molecules in an open lattice, increasing volume and lowering density.

Correct: (C)

O2 has a double bond, O=O, so its bond order is 2.

Correct: (B)

Formal charge = 5 – (0 + 8/2) = +1.

Correct: (A)

Group 1 metals become more reactive down the group because the outer electron is farther from the nucleus and more easily lost.

Correct: (C)

Aluminium is the Period 3 element in Group 13.

Correct: (D)

Transition metals commonly form ions with different charges, such as Fe^2+ and Fe^3+.

Correct: (B)

Acyclic alkanes have the general formula CnH2n+2.

Correct: (B)

The -OH hydroxyl group makes ethanol an alcohol.

Correct: (D)

Fluorine is the most electronegative element.

Correct: (C)

Elements become less metallic and more non-metallic across a period.

Correct: (A)

Structural isomers share a molecular formula but differ in how atoms are connected.

Correct: (C)

Standard enthalpy changes are measured for heat transfer at constant pressure.

Correct: (A)

q = mcΔT = 50.0 x 2.00 x 10.0 = 1000 J = 1.00 kJ.

Correct: (B)

Enthalpy is a state function, so the overall change depends only on the starting and finishing states.

Correct: (D)

Bond enthalpy refers to breaking one mole of a bond in gaseous molecules, averaged over similar compounds where relevant.

Correct: (D)

Endothermic reactions absorb heat, so the products have higher enthalpy than the reactants.

Correct: (B)

Gases have much greater disorder than liquids or solids, so steam has the greatest entropy.

Correct: (A)

With ΔG = ΔH – TΔS, negative ΔH and positive ΔS make ΔG negative at all temperatures.

Correct: (C)

Atomization produces one mole of gaseous atoms from the element under standard conditions.

Correct: (A)

Particles must collide with enough energy and the correct geometry to react.

Correct: (C)

The area is proportional to the total number of particles in the sample and stays constant for a fixed sample.

Correct: (B)

The exponent of [X] in the rate law is 2, so the reaction is second order in X.

Correct: (D)

Large Kc means the equilibrium concentration of products is much greater than that of reactants.

Correct: (B)

Added heat shifts equilibrium in the direction that absorbs heat, which is the endothermic direction.

Correct: (D)

K depends on temperature; changing concentration or pressure changes position, not K.

Correct: (A)

At equilibrium [A] = 0.80 – 0.30 = 0.50, so Kc = [B]/[A] = 0.30/0.50 = 0.60.

Correct: (C)

A catalyst provides an alternative pathway requiring less activation energy.

Correct: (C)

Unlike first-order reactions, second-order half-life changes with the starting concentration.

Correct: (A)

Rate is concentration change per unit time, commonly mol dm^-3 s^-1.

Correct: (D)

At constant volume the reactant and product partial pressures do not change, so there is no shift.

Correct: (B)

Pure solids are omitted from the expression, leaving Kc = [CO2].

Correct: (D)

[OH^-] = 0.0010, so pOH = 3.00 and pH = 14.00 – 3.00 = 11.00.

Correct: (B)

NH4^+ is the conjugate acid of a weak base and donates H^+ to water, making the solution acidic.

Correct: (C)

Larger Ka means a greater extent of ionisation, so the acid is stronger.

Correct: (A)

Reduction is gain of electrons, with a decrease in oxidation number.

Correct: (A)

Metal ions are reduced at the cathode; in an electrolytic cell the cathode is connected to the negative terminal.

Correct: (D)

Hydrogen is oxidized and oxygen is reduced, giving water as the overall product.

Correct: (B)

The slow step of SN1 is unimolecular and involves only the halogenoalkane forming a carbocation.

Correct: (C)

Substitution replaces one H atom while keeping the delocalized aromatic system intact.

Correct: (B)

The carbonyl carbon in a ketone is bonded to two carbon groups, so reduction gives a secondary alcohol.

Correct: (C)

By Henderson-Hasselbalch, pH = pKa + log([base]/[acid]); with equal concentrations the log term is 0, so pH = 4.76.

Correct: (A)

Sulfur dioxide dissolves to form sulfurous acid and can be oxidized further to sulfuric acid in acid rain chemistry.

Correct: (D)

The standard hydrogen electrode is the reference electrode and is assigned E = 0.00 V.