IB Chemistry Practice Test 10

Correct: (D)

The number of molecules is proportional to the amount in moles, and 0.30 mol is the largest amount listed.

Correct: (C)

Mg (12 electrons) loses its two 3s electrons, leaving 10 electrons with configuration 1s^2 2s^2 2p^6, the same as Ne.

Correct: (B)

Mr = 40 + 2 × (16 + 1) = 40 + 34 = 74.

Correct: (A)

n = m / Mr = 11.0 / 44.0 = 0.250 mol.

Correct: (D)

Moles of HCl stay constant: 0.0250 × 2.00 = 0.0500 mol; c = 0.0500 / 0.250 = 0.200 mol dm^-3.

Correct: (C)

Ar = (0.75 × 35) + (0.25 × 37) = 26.25 + 9.25 = 35.5.

Correct: (B)

0.500 mol NaCl contains 0.500 mol Na^+ and 0.500 mol Cl^-, a total of 1.00 mol of ions = 6.02 × 10^23 ions.

Correct: (A)

The mole ratio is already in its simplest whole-number form, so the empirical formula is C2H6O.

Correct: (C)

V = nRT / p = (2.00 × 8.31 × 300) / 100000 = 0.0499 m^3 = 49.9 dm^3.

Correct: (D)

Mg has 12 electrons; Mg^2+ has lost two, leaving 10 electrons per ion, so 1.00 mol of ions contains 10.0 mol of electrons.

Correct: (B)

Boron has three bonding pairs and no lone pair, so the atoms lie in one plane with 120° bond angles.

Correct: (A)

Caesium and fluorine have the largest electronegativity difference of the pairs listed, giving the most ionic bond.

Correct: (D)

HCl is polar but hydrogen bonding needs H attached to N, O or F, so dipole-dipole forces dominate between HCl molecules.

Correct: (C)

Carbon in CO2 has two electron domains (two double bonds) that repel to opposite sides, making the molecule linear.

Correct: (A)

Every carbon in diamond is covalently bonded to four others in a rigid 3D network, so breaking it means breaking strong covalent bonds.

Correct: (B)

N2 contains a triple bond, which consists of three shared pairs, i.e. 6 electrons.

Correct: (C)

Iodine exists as discrete I2 molecules; NaCl is ionic, Mg is metallic and diamond is giant covalent.

Correct: (D)

Only HF forms hydrogen bonds between its molecules, giving it an anomalously high boiling point despite its low molar mass.

Correct: (B)

Carbon has four bonding pairs and no lone pairs; they repel to the corners of a tetrahedron.

Correct: (A)

The delocalized electrons hold the ions together in their new positions when layers slide, so the metal changes shape without shattering.

Correct: (C)

Group 17 elements (F, Cl, Br, I) are the halogens; group 18 are the noble gases and group 1 are the alkali metals.

Correct: (B)

Down group 1 the outer electron is further from the nucleus and more shielded, so it is lost more easily and reactivity increases.

Correct: (A)

Transition metals characteristically form compounds with different oxidation states, as well as coloured ions and catalytic activity.

Correct: (D)

The C=O group is bonded to two carbons within the chain, making propanone a ketone, not an aldehyde.

Correct: (B)

Saturated acyclic hydrocarbons have the general formula CnH2n+2.

Correct: (C)

The element has 6 electrons in its outer shell, placing it in group 16 (period 3, sulfur).

Correct: (D)

Non-metal oxides such as SO2 are acidic; Na2O and MgO are basic oxides and NH3 is a base, not an oxide.

Correct: (A)

Each successive member of a homologous series has one extra -CH2- unit, with a gradual change in physical properties.

Correct: (B)

A positive ΔH means the products have more enthalpy than the reactants, so heat is absorbed: the reaction is endothermic.

Correct: (D)

c = q / (mΔT) = 1000 / (50.0 × 20.0) = 1.00 J g^-1 °C^-1.

Correct: (C)

Reversing a reaction changes the sign of ΔH, so the decomposition of ammonia is endothermic with ΔH = +92 kJ mol^-1.

Correct: (A)

Energy must be supplied to break bonds, while energy is released when new bonds form.

Correct: (D)

A negative Gibbs energy change means the reaction is thermodynamically spontaneous (feasible) under those conditions.

Correct: (B)

Condensation turns a gas into a liquid, so the particles become much more ordered and entropy decreases.

Correct: (A)

Less measured heat means q is underestimated, so the calculated |ΔH| is smaller than the true value.

Correct: (C)

Standard conditions are a pressure of 100 kPa (1 bar) with a specified temperature, commonly 298 K.

Correct: (A)

Rate is the change in concentration per unit time; the negative sign makes the rate positive for a reactant being used up.

Correct: (D)

t1/2 = 0.693 / 0.0693 = 10.0 s.

Correct: (B)

Only collisions with energy at least equal to the activation energy can lead to products.

Correct: (C)

More particles in the same volume collide more often, so successful collisions happen more frequently.

Correct: (D)

A large Kc means the equilibrium mixture contains far more products than reactants; it says nothing about the rate.

Correct: (A)

There are 3 mol of gas on the left and 2 mol on the right; higher pressure favours the side with fewer gas molecules, the products.

Correct: (C)

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

Correct: (B)

A fourfold rate increase on doubling concentration (2^2 = 4) shows the reaction is second order in B.

Correct: (A)

At higher temperature many more particles exceed the activation energy, so the rate rises sharply, as shown by the Maxwell-Boltzmann distribution.

Correct: (C)

At equilibrium the forward and reverse reactions continue at equal rates, so observable properties stay constant.

Correct: (D)

A catalyst speeds up both directions by the same factor, so equilibrium is reached faster but its position is unchanged.

Correct: (B)

If Q is less than Kc, more products must form to raise Q to Kc, so the net reaction goes forward.

Correct: (D)

The strongest acid has the weakest conjugate base; HCl is a strong acid, so Cl^- is an extremely weak base.

Correct: (B)

NaOH is a strong base, so [OH^-] = 0.010 and pOH = -log(0.010) = 2.00.

Correct: (A)

Oxidation is the loss of electrons (OILRIG: Oxidation Is Loss, Reduction Is Gain).

Correct: (C)

With concentrated chloride solution, Cl^- ions are discharged at the anode to form chlorine gas; hydrogen forms at the cathode.

Correct: (B)

By the Henderson-Hasselbalch equation, pH = pKa + log([salt]/[acid]) = 4.74 + log(1) = 4.74.

Correct: (D)

Let the oxidation number of Mn be x: x + 4(-2) = -1, so x = +7.

Correct: (A)

UV light provides the energy to split Br2 into free radicals, starting the free radical substitution chain reaction.

Correct: (C)

A nucleophile donates a pair of electrons to an electron-deficient centre; an electrophile accepts a pair.

Correct: (D)

Acid hydrolysis splits the ester at the ester link, regenerating the carboxylic acid and the alcohol.

Correct: (A)

The anion of the weak acid hydrolyses to produce OH^-, so the equivalence point of a weak acid-strong base titration is alkaline (pH greater than 7).

Correct: (B)

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

Correct: (C)

Addition polymerization opens the C=C bond of monomers such as ethene so they can join into a long chain with no by-product.