IB Chemistry Practice Test 9

Correct: (A)

CH4 gives 0.50 × 5 = 2.50 mol of atoms, more than He (1.00), CO2 (1.20) and C2H6 (2.40).

Correct: (B)

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

Correct: (C)

Protons = 17, neutrons = 37 – 17 = 20, and the -1 charge means one extra electron, so 18 electrons.

Correct: (D)

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

Correct: (A)

Volume = 0.250 × 22.7 = 5.68 dm^3.

Correct: (B)

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

Correct: (C)

Number of molecules = 0.0200 × 6.02 × 10^23 = 1.20 × 10^22.

Correct: (D)

The two N atoms contribute 28.0 of the 80.0 mass, so (28.0 / 80.0) × 100 = 35.0%.

Correct: (B)

p = nRT / V = (0.500 × 8.31 × 300) / 0.0100 = 1.25 × 10^5 Pa = 125 kPa.

Correct: (A)

The electron mass is about 1/1836 of a proton mass, far smaller than a proton, neutron or alpha particle.

Correct: (C)

Nitrogen has three bonding pairs and one lone pair; the lone pair makes the molecular shape trigonal pyramidal.

Correct: (D)

MgO is formed between a metal and a non-metal with electron transfer, giving Mg^2+ and O^2- ions.

Correct: (A)

Oxygen has six valence electrons; two are used in O-H bonds, leaving four electrons as two lone pairs.

Correct: (B)

Water forms hydrogen bonds between molecules, which are stronger than the van der Waals and dipole forces in the other liquids.

Correct: (D)

Four bonding pairs arrange tetrahedrally around carbon, giving a bond angle of 109.5°.

Correct: (C)

Carbon contributes 4 and each oxygen contributes 6, so 4 + 6 + 6 = 16 valence electrons.

Correct: (A)

In graphite each carbon forms three bonds and the fourth electron is delocalized within the layers, allowing conduction.

Correct: (B)

CO2 is linear and symmetrical, so the two bond dipoles cancel and the molecule has no overall dipole.

Correct: (C)

Metals consist of a lattice of positive ions surrounded by a sea of delocalized electrons, and the attraction is the metallic bond.

Correct: (D)

SiO2 is a giant covalent network of atoms joined by covalent bonds throughout the structure.

Correct: (A)

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

Correct: (C)

Aluminium oxide reacts with both acids and strong bases, so it is amphoteric, unlike the basic group 1/2 oxides and acidic P4O10.

Correct: (B)

Transition metal compounds are typically coloured and the metals show variable oxidation states and catalytic activity.

Correct: (D)

The -COOH group makes the compound propanoic acid, a carboxylic acid.

Correct: (C)

Acyclic alkenes with one C=C bond have the general formula CnH2n.

Correct: (A)

More protons attract the outer electrons more strongly while shielding stays similar, so more energy is needed to remove an electron.

Correct: (D)

Zinc is a d-block element; Ca and Na are s-block and Al is p-block.

Correct: (B)

The -OH group is on a carbon joined to only one other carbon, so propan-1-ol is a primary alcohol.

Correct: (D)

Exothermic reactions lose heat to the surroundings, so the products have lower enthalpy than the reactants and ΔH is negative.

Correct: (A)

q = mcΔT = 100 × 4.18 × 5.0 = 2090 J = 2.09 kJ.

Correct: (B)

By Hess's law, subtract the second equation from the first: -393 – (-283) = -110 kJ mol^-1.

Correct: (C)

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

Correct: (A)

A gas is produced from a solid, greatly increasing the disorder of the system; the other changes all decrease disorder.

Correct: (D)

ΔG = ΔH – TΔS = -100 – 298 × (-0.200) = -100 + 59.6 = -40.4 kJ mol^-1.

Correct: (B)

Formation means making one mole of a compound from its elements in their standard states under standard conditions.

Correct: (C)

Enthalpy change scales with amount: 2.00 × (-890) = -1780 kJ.

Correct: (B)

The rate is proportional to [A] only, so it is first order in A and zero order in B: rate = k[A].

Correct: (C)

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

Correct: (D)

At higher temperature the distribution spreads over higher energies, so the peak shifts right and falls, while the total area stays constant.

Correct: (A)

A catalyst offers a different reaction pathway needing less activation energy, so more collisions are successful.

Correct: (C)

Products are placed on top and each concentration is raised to its stoichiometric coefficient: Kc = [NH3]^2 / ([N2][H2]^3).

Correct: (B)

Raising the temperature favours the endothermic direction, which for this exothermic forward reaction is the reverse direction, towards the reactants.

Correct: (A)

Kc = [HI]^2 / ([H2][I2]) = 0.60^2 / (0.20 × 0.20) = 0.36 / 0.040 = 9.0.

Correct: (D)

For first-order reactions t1/2 = ln 2 / k, which contains no concentration term.

Correct: (B)

Tripling concentration gives 3^2 = 9 times the rate, the pattern for second-order dependence.

Correct: (A)

At equilibrium both reactions still occur but at equal rates, so concentrations remain constant, though not necessarily equal.

Correct: (D)

Kp = Kc(RT)^Δn and here Δn = 2 – 2 = 0, so Kp = Kc.

Correct: (C)

Increasing the pressure favours the side with fewer gas molecules, reducing the pressure again (Le Chatelier's principle).

Correct: (C)

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

Correct: (A)

Removing one H^+ from HCO3^- leaves CO3^2-, its conjugate base.

Correct: (D)

A buffer needs a weak acid together with its conjugate base, usually supplied as a salt of the weak acid.

Correct: (B)

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

Correct: (A)

Oxidation always takes place at the anode, and in a galvanic cell the anode is the negative electrode.

Correct: (D)

Pb^2+ ions are reduced at the negative cathode to lead metal; bromine forms at the anode.

Correct: (C)

HCO3^- can donate a proton (forming CO3^2-) or accept a proton (forming H2CO3), so it is amphiprotic.

Correct: (B)

The C=C bond breaks and H and Br add to the two carbons, giving bromoethane: an addition reaction.

Correct: (D)

The tertiary halide forms the most stable carbocation intermediate, so it reacts fastest by SN1.

Correct: (C)

Zn is oxidized (0 to +2), and the species that is oxidized causes reduction, so Zn is the reducing agent.

Correct: (B)

The most negative E value means the metal is most easily oxidized, so lithium is the strongest reducing agent.

Correct: (A)

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