IB Chemistry Practice Test 4

Correct: (A)

Each NaCl formula unit forms two ions, so 0.500 mol of NaCl forms 1.00 mol of ions, which is 6.02 × 10^23 ions.

Correct: (C)

A magnesium atom loses its two 3s electrons, leaving the neon configuration 1s^2 2s^2 2p^6.

Correct: (D)

Molar mass = 6(12.01) + 12(1.008) + 6(16.00) = 180 g mol^-1 to three significant figures.

Correct: (B)

p = nRT / V = (0.200 × 8.31 × 300) / 5.00 = 99.7 kPa.

Correct: (A)

Percentage of H = (2 × 1.008 / 18.02) × 100 = 11.1%.

Correct: (C)

The amount of acid does not change. Concentration = 2.00 × (25.0 / 250) = 0.200 mol dm^-3.

Correct: (D)

The mole ratio CH4:O2 is 1:2, so 0.500 mol of methane requires 1.00 mol of oxygen.

Correct: (B)

Average mass = (0.200 × 10) + (0.800 × 11) = 10.8.

Correct: (A)

Mole ratio = C: 40.0 / 12 = 3.33, H: 6.70 / 1 = 6.70, O: 53.3 / 16 = 3.33. Dividing by 3.33 gives 1:2:1, so the empirical formula is CH2O.

Correct: (C)

The peaks account for 2 + 2 + 6 + 2 = 12 electrons, which is magnesium.

Correct: (D)

Ionic compounds consist of positive and negative ions held together by electrostatic attraction in a lattice.

Correct: (B)

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

Correct: (A)

Hydrogen attached to the very electronegative fluorine atom can form hydrogen bonds with neighbouring molecules.

Correct: (C)

Silicon and oxygen atoms are joined by covalent bonds in a continuous three-dimensional network.

Correct: (D)

Each carbon atom contributes an electron to a delocalized system within a layer, allowing charge to move.

Correct: (B)

Ethene has four C-H sigma bonds and one C-C sigma bond, for a total of five sigma bonds. The second component of the double bond is a pi bond.

Correct: (A)

Carbon dioxide forms a simple molecular solid with weak forces between molecules. The other solids have giant structures with strong bonding throughout.

Correct: (C)

Formal charge = 5 valence electrons – [0 non-bonding electrons + 1/2(8 bonding electrons)] = +1.

Correct: (D)

Fluorine has the greatest electronegativity of these atoms, so the H-F bond has the largest electronegativity difference.

Correct: (B)

The best Lewis structure of CN- has a triple bond between carbon and nitrogen.

Correct: (A)

Metal oxides on the left are basic, aluminium oxide is amphoteric, and non-metal oxides toward the right are acidic.

Correct: (C)

Iron is [Ar] 4s^2 3d^6. Forming Fe^3+ removes the two 4s electrons and one 3d electron, leaving [Ar] 3d^5.

Correct: (D)

Chlorine oxidizes Br- to Br2 because chlorine is more reactive and is a stronger oxidizing agent.

Correct: (B)

A saturated acyclic alcohol with one hydroxyl group has the general formula CnH2n+1OH.

Correct: (A)

An ester contains a carbon atom double-bonded to oxygen and single-bonded to another oxygen atom, written as -COO-.

Correct: (C)

The configuration contains 26 electrons in a neutral atom, so the element is iron, Fe.

Correct: (D)

Down Group 1, the outer electron is in a shell farther from the nucleus and experiences more shielding, so it is removed more easily.

Correct: (B)

Isomers have identical molecular formulas. Structural isomers differ in how their atoms are connected.

Correct: (A)

Standard enthalpy of combustion refers to complete combustion of one mole of a substance in oxygen under standard conditions.

Correct: (C)

Heat absorbed by the water = 200 × 4.18 × 3.00 = 2510 J, so the reaction released 2510 J.

Correct: (D)

The target equation is twice the given equation, so ΔH = 2 × (-283) = -566 kJ.

Correct: (B)

Bonds broken = 436 + 159 = 595 kJ. Bonds formed = 2 × 567 = 1134 kJ. ΔH = 595 – 1134 = -539 kJ mol^-1.

Correct: (A)

An endothermic reaction absorbs energy, so the products have greater enthalpy than the reactants and ΔH is positive.

Correct: (C)

The reaction converts 3 mol of gas into 2 mol of gas, reducing the number of freely moving particles.

Correct: (D)

ΔG = ΔH – TΔS. With both terms positive, the -TΔS term can make ΔG negative only when T is high enough.

Correct: (B)

Strong acid and strong base neutralizations are dominated by H+(aq) + OH-(aq) → H2O(l), with ΔH of about -57 kJ mol^-1.

Correct: (A)

The rate is directly proportional to [B], so it is first order in B, and it is zero order in A.

Correct: (C)

The catalysed pathway lowers the energy of the transition state relative to both reactants and products.

Correct: (D)

A catalyst does not change the energies of the particles. It lowers the activation energy, so a larger fraction of collisions is successful.

Correct: (B)

Concentrations are raised to their stoichiometric coefficients: two for SO3, two for SO2 and one for O2.

Correct: (A)

Kc = [B] / [A] = 0.750 / 0.250 = 3.00.

Correct: (C)

Decreasing the volume increases the pressure. The equilibrium shifts toward the side with fewer moles of gas, which is the product side with 2 mol rather than 3 mol.

Correct: (D)

At dynamic equilibrium, both reactions continue at the same rate, so the macroscopic concentrations remain constant.

Correct: (B)

For a first-order reaction, rate = k[A]. Therefore k = rate / concentration, and the concentration units cancel, leaving s^-1.

Correct: (A)

For zero-order kinetics, t1/2 = [A]0 / 2k, so a larger initial concentration gives a longer half-life.

Correct: (C)

The exponential term in the Arrhenius equation increases with temperature, so more molecular collisions can overcome the activation energy barrier.

Correct: (D)

The added chloride ion increases [Cl-], so the dissolution equilibrium shifts left and less AgCl dissolves.

Correct: (B)

Q is less than Kc, so more product must form until Q equals Kc.

Correct: (A)

[OH-] = 0.00100, so pOH = 3.00 and pH = 14.00 – 3.00 = 11.0.

Correct: (C)

[H+] = 1.0 × 10^-3. Ka is approximately [H+]^2 / 0.100 = (1.0 × 10^-3)^2 / 0.100 = 1.0 × 10^-5 mol dm^-3.

Correct: (D)

At the equivalence point, the amounts of acid and base match the stoichiometry of the reaction. The end point is the observed indicator change close to it.

Correct: (B)

NH4+ is the conjugate acid of NH3 and donates a proton to water, producing H3O+.

Correct: (A)

The oxidation states sum to zero: 2(+1) + S + 4(-2) = 0, so S = +6.

Correct: (C)

Zinc has the most negative reduction potential, so Zn is oxidized most readily and is the strongest reducing agent of the three metals.

Correct: (D)

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

Correct: (B)

Pb^2+ ions move to the cathode and are reduced: Pb^2+ + 2e- → Pb.

Correct: (A)

OH- donates a pair of electrons to the electron-deficient carbon bonded to bromine, beginning nucleophilic substitution.

Correct: (C)

Ultraviolet light supplies energy for Cl2 to split into two chlorine radicals, one electron going to each atom.

Correct: (D)

Under reflux with excess oxidizing agent, a primary alcohol is oxidized fully to the carboxylic acid.

Correct: (B)

A buffer needs significant amounts of a weak acid and its conjugate base so it can react with added H+ or OH-.