Chemistry Practice

QUESTION 1 [1 mark]

Multiple choice Foundation No calculator About 1.5 min

Which sample consists of an element?

A Neon gas B Distilled water C Seawater D Brass

Show worked solution

Correct answer: A

Reasoning: An element contains only one type of atom and cannot be decomposed chemically. Neon is made only of neon atoms. Water is a compound, while seawater and brass are mixtures. Therefore option A is correct.

QUESTION 2 [1 mark]

Multiple choice Standard No calculator About 1.5 min

The diagrams show equal numbers of identical particles in three containers of equal volume. Which assignment of physical states is correct?

A X liquid, Y solid, Z gas B X solid, Y liquid, Z gas C X solid, Y gas, Z liquid D X gas, Y liquid, Z solid

Show worked solution

Correct answer: B

Reasoning: X has closely packed particles in a regular arrangement, so it represents a solid. Y has closely packed particles with no fixed arrangement, so it represents a liquid. Z has widely separated particles, so it represents a gas. Option B is correct.

QUESTION 3 [2 marks]

Short response Standard Calculator About 3 min

Two samples of the same ideal gas are at $300\,\mathrm{K}$ and $450\,\mathrm{K}$. Determine the ratio of their average translational kinetic energies, $\overline{E}_{k,450}/\overline{E}_{k,300}$.

Show worked solution

For an ideal gas, average translational kinetic energy is directly proportional to absolute temperature: $\overline{E}_k\propto T$.

$$\frac{\overline{E}_{k,450}}{\overline{E}_{k,300}}=\frac{450}{300}=1.50$$

Final answer: $1.50$

QUESTION 4 [3 marks]

Data-based Standard No calculator About 4.5 min

A pure substance is heated at constant pressure. Use the heating curve to identify the process occurring during section B and explain why the temperature remains constant.

Show worked solution

Section B is the first horizontal region, so it represents melting.

Energy supplied during melting overcomes attractions between particles and increases potential energy.

The average kinetic energy does not increase, so the temperature stays constant until the phase change is complete.

Final answer: Melting; the supplied energy changes potential energy rather than average kinetic energy.

QUESTION 5 [2 marks]

Short response Foundation No calculator About 3 min

Molten sodium chloride can be decomposed by electrolysis into sodium and chlorine. Explain why sodium chloride is not an element.

Show worked solution

Reasoning: An element cannot be broken down into simpler substances by chemical means. Electrolysis chemically separates sodium chloride into two different elements, sodium and chlorine. Sodium chloride must therefore be a compound.

Final answer: It is a compound because chemical decomposition produces two elements.

QUESTION 6 [4 marks]

Multi-part Applied No calculator About 6 min

A sealed flask contains liquid bromine and bromine vapour at constant temperature. (a) Describe the particle arrangement and motion in each phase. (b) Explain why the amount of liquid remains constant.

Show worked solution

(a) In the liquid, particles are close together, disordered and move past one another. In the vapour, they are far apart and move rapidly in random directions.
(b) A dynamic equilibrium is established: the rates of evaporation and condensation are equal, so there is no net change in the amount of liquid.

Final answer: (a) Liquid: close and mobile; vapour: widely separated and random. (b) Evaporation rate equals condensation rate.

QUESTION 7 [1 mark]

Multiple choice Standard No calculator About 2 min

Which sample is a mixture?

A Pure copper B Carbon dioxide C Brass D Deionized water

Show worked solution

Correct answer: C

Reasoning: Brass contains copper and zinc in variable proportions; the other samples name elements or compounds. Therefore option C is correct.

QUESTION 8 [1 mark]

Multiple choice Standard No calculator About 2 min

Which description applies to a liquid?

A Particles occupy fixed lattice positions B Particles remain close but move past one another C Particles are widely separated with negligible attractions D The sample has a fixed shape

Show worked solution

Correct answer: B

Reasoning: Liquid particles remain close together but can move, giving fixed volume and variable shape. Therefore option B is correct.

QUESTION 9 [1 mark]

Multiple choice Standard No calculator About 2 min

Which method separates sand from aqueous sodium chloride before recovering the salt?

A Filtration B Paper chromatography C Simple distillation only D Sublimation

Show worked solution

Correct answer: A

Reasoning: Sand is insoluble and is retained by filter paper while the salt solution passes through. Therefore option A is correct.

QUESTION 10 [1 mark]

Multiple choice Standard No calculator About 2 min

A substance melts at $-114\,^{\circ}\mathrm C$. What is this temperature on the kelvin scale?

A 159 K B 387 K C -159 K D -387 K

Show worked solution

Correct answer: A

Reasoning: Convert using $T/\mathrm K=\theta/^{\circ}\mathrm C+273$: $-114+273=159$ K. Therefore option A is correct.

QUESTION 11 [1 mark]

Multiple choice Standard No calculator About 2 min

The chromatogram was developed with ethanol. Which spot has the greater affinity for the mobile phase, and what is the mobile phase?

A P; ethanol B P; paper C Q; ethanol D Q; paper

Show worked solution

Correct answer: A

Reasoning: P travelled farther from the baseline, showing greater attraction to the moving ethanol solvent. Therefore option A is correct.

QUESTION 12 [1 mark]

Multiple choice Standard No calculator About 2 min

Which listed samples are mixtures? I. Air II. Bronze III. Pure ammonia

A I only B I and II only C II and III only D I, II and III

Show worked solution

Correct answer: B

Reasoning: Air and bronze contain more than one substance in variable proportions; pure ammonia is a compound. Therefore option B is correct.

QUESTION 13 [1 mark]

Multiple choice Standard No calculator About 2 min

Which statement about vaporization of a liquid is correct?

A It is exothermic and liquids are readily compressed B It is endothermic and liquids are not readily compressed C It is exothermic and particles separate D It is endothermic and particles become fixed

Show worked solution

Correct answer: B

Reasoning: Energy is absorbed to overcome attractions during vaporization, while closely packed liquid particles make compression difficult. Therefore option B is correct.

QUESTION 14 [6 marks]

Multi-part Standard No calculator About 9 min

Magnesium burns in oxygen to form magnesium oxide. (a) Classify magnesium, oxygen and magnesium oxide as element or compound. (b) Name the change from gaseous iodine directly to solid iodine. (c) Explain why clean air is described as a homogeneous mixture.

Show worked solution

(a) Mg and O$_2$ are elements; MgO is a compound because different elements are chemically combined in a fixed ratio.
(b) Deposition.
(c) Air contains several gases physically mixed and uniformly distributed on the macroscopic scale.

Final answer: Mg and O$_2$: elements; MgO: compound; deposition; air is a uniform mixture of gases.

QUESTION 15 [1 mark]

Multiple choice Standard No calculator About 2 min

On the heating curve, which statement is correct?

A Temperature rises during both plateaus B The first plateau represents melting C Only solid is present throughout the first plateau D Average kinetic energy rises during a plateau

Show worked solution

Correct answer: B

Reasoning: At the first horizontal region, supplied energy overcomes attractions while solid and liquid coexist; temperature and average kinetic energy remain constant. Therefore option B is correct.

QUESTION 16 [1 mark]

Multiple choice Standard No calculator About 2 min

A dissolved solid must be recovered from a flammable solvent. Which procedure is safest?

A Heat directly with a Bunsen flame B Use a warm water bath in a ventilated area C Filter the solution D Add more flammable solvent and ignite

Show worked solution

Correct answer: B

Reasoning: Indirect heating avoids a naked flame while allowing solvent evaporation; filtration cannot remove a dissolved solid. Therefore option B is correct.

QUESTION 17 [1 mark]

Multiple choice Standard No calculator About 2 min

Which statements describe condensation? I. Gas changes to liquid. II. Energy is released to the surroundings. III. Molecules become locked in fixed lattice positions.

A I only B I and II only C II and III only D I, II and III

Show worked solution

Correct answer: B

Reasoning: Condensation is gas to liquid and is exothermic. Fixed lattice positions describe freezing to a solid. Therefore option B is correct.

QUESTION 18 [7 marks]

Multi-part Standard Calculator About 11 min

A pigment chromatogram has a solvent front 8.0 cm above the baseline. Red, blue and yellow spots are at 6.0, 4.0 and 2.0 cm. (a) Calculate each $R_f$. (b) Identify the pigment with greatest affinity for the stationary phase. (c) Explain why a sample producing three spots is a mixture.

Show worked solution

(a) $R_f=\text{distance by solute}/\text{distance by solvent}$: red 0.75, blue 0.50, yellow 0.25.
(b) Yellow has the greatest stationary-phase affinity because it travelled least.
(c) Three separated spots show at least three components with different relative attractions.

Final answer: $R_f$: 0.75, 0.50, 0.25; yellow has greatest stationary-phase affinity; three spots show a mixture.

QUESTION 19 [1 mark]

Multiple choice Standard No calculator About 2 min

A mixture contains iron filings, insoluble chalk and sodium chloride solution. Which sequence can isolate all three components?

A Magnet, filtration, evaporation B Evaporation, magnet, chromatography C Filtration, distillation, magnet D Chromatography, magnet, filtration

Show worked solution

Correct answer: A

Reasoning: A magnet first removes iron, filtration removes chalk, and evaporation or crystallization recovers sodium chloride. Therefore option A is correct.

QUESTION 20 [9 marks]

Multi-part Standard No calculator About 14 min

Ethanol melts at $-114^{\circ}\mathrm C$ and boils at $78^{\circ}\mathrm C$. (a) Describe a labelled heating curve from $-130^{\circ}\mathrm C$ to $100^{\circ}\mathrm C$. (b) State its phase at $20^{\circ}\mathrm C$. (c) Describe particle arrangement and motion at $20^{\circ}\mathrm C$. (d) Suggest how insoluble sodium sulfate could be separated and both substances recovered.

Show worked solution

(a) Rising solid segment, plateau at −114 °C, rising liquid segment, plateau at 78 °C, then rising gas segment.
(b) Liquid.
(c) Molecules are close, randomly arranged and able to move past one another.
(d) Filter to retain and dry the solid, then distil the filtrate to recover ethanol.

Final answer: Heating curve with plateaus at −114 °C and 78 °C; ethanol is liquid at 20 °C; filter then distil.

QUESTION 21 [7 marks]

Multi-part Standard No calculator About 11 min

A heating curve for water begins at $-15^{\circ}\mathrm C$ and ends at $115^{\circ}\mathrm C$. (a) Name the phase or phases in each of the five regions. (b) State the melting temperature. (c) Explain what happens to potential and kinetic energy during boiling.

Show worked solution

(a) Solid; solid + liquid; liquid; liquid + gas; gas.
(b) $0^{\circ}\mathrm C$ at standard pressure.
(c) Temperature and average kinetic energy remain constant while potential energy rises as intermolecular attractions are overcome.

Final answer: Solid → solid/liquid → liquid → liquid/gas → gas; melting at 0 °C; potential energy rises during boiling.

QUESTION 22 [9 marks]

Multi-part No calculator About 14 min

River water contains gravel, suspended clay, dissolved salt and two water-soluble dyes. Design a separation sequence that obtains the gravel, clay, water, salt and separated dye samples. State the property used at each stage.

Show worked solution

First sieve the gravel by particle size. Filter the remaining suspension to retain clay. Distil the filtrate: water is collected according to volatility, leaving salt and dyes. Dissolve the residue in a small suitable solvent and use chromatography to separate the dyes by different affinities. Crystallization or selective extraction can then separate salt from organic dyes.

Final answer: Sieve → filter → distil → chromatographic separation, with crystallization/selective extraction for salt.

QUESTION 23 [1 mark]

Multiple choice Standard No calculator About 2 min

A chromatogram of a dye shows two spots before recrystallization and one spot afterward. What conclusion is justified?

A The solvent was impure B A coloured impurity was removed C The product decomposed into two substances D Recrystallization always changes $R_f$

Show worked solution

Correct answer: B

Reasoning: The original two components separate into two spots; one remaining spot after treatment is evidence that the detected impurity was removed. Therefore option B is correct.

QUESTION 24 [1 mark]

Multiple choice Standard No calculator About 2 min

Paper chromatography is best suited to separating which sample?

A Sand from water B Several soluble food dyes C Oil droplets from water D Iron filings from sulfur

Show worked solution

Correct answer: B

Reasoning: Dissolved dye components partition differently between the mobile solvent and stationary paper. Therefore option B is correct.

QUESTION 25 [1 mark]

Multiple choice Standard No calculator About 2 min

Methanol boils at $65^{\circ}\mathrm C$. Which statements are correct? I. Evaporation can occur at $40^{\circ}\mathrm C$. II. Condensation can occur at $65^{\circ}\mathrm C$. III. At $80^{\circ}\mathrm C$ and 1 atm, methanol particles are close together in a liquid.

A I only B II only C I and II only D I, II and III

Show worked solution

Correct answer: C

Reasoning: Evaporation occurs below boiling point and condensation can occur at the boiling point. At 80 °C and 1 atm methanol is gaseous, so III is false. Therefore option C is correct.

QUESTION 26 [4 marks]

Standard No calculator About 6 min

Classify each observation as supporting a pure element, pure compound or mixture: A is a silvery conductor that forms one oxide; B is a white solid with a sharp melting point and decomposes into two elements; C melts over a broad range and separates into two spots by chromatography.

Show worked solution

A supports a pure element: it has metallic properties and forms a compound on reaction. B supports a pure compound: it has a sharp melting point and can be chemically decomposed. C supports a mixture: a melting range and multiple chromatographic spots show more than one component.

Final answer: A: element; B: compound; C: mixture.

QUESTION 27 [1 mark]

Multiple choice Standard No calculator About 2 min

A mixture gives spots at the same heights as standards X and Z, plus one additional spot. Which conclusion is valid?

A Only X is present B X and Z are present, with at least one other component C The mixture contains exactly two components D Z is absent

Show worked solution

Correct answer: B

Reasoning: Matching $R_f$ positions support the presence of X and Z, and the additional spot indicates at least one further component. Therefore option B is correct.

QUESTION 28 [1 mark]

Multiple choice Standard No calculator About 2 min

Which method and property separate a liquid mixture of methanol and ethanol?

A Filtration using particle size B Fractional distillation using boiling-point difference C Chromatography using ionic charge D Decanting using colour

Show worked solution

Correct answer: B

Reasoning: The miscible liquids have different boiling points, and a fractionating column permits repeated vaporization-condensation steps. Therefore option B is correct.

QUESTION 29 [1 mark]

Multiple choice Standard No calculator About 2 min

A solid melts gradually from 128 to 132 °C. Reference values are benzoic acid 121 °C, benzamide 129 °C and cinnamic acid 133 °C. Which conclusion is defensible?

A It is certainly pure benzamide B It may be impure cinnamic acid or benzamide; another test is needed C It must be benzoic acid D Melting range cannot indicate purity

Show worked solution

Correct answer: B

Reasoning: A broad, depressed range suggests impurity and the overlap prevents unique identification. Therefore option B is correct.

QUESTION 30 [1 mark]

Multiple choice Standard No calculator About 2 min

A beaker contains seawater contaminated with sand. The mixture is filtered and the filtrate is distilled. Which statement is correct?

A Sand is present in the filtrate B Pure sodium chloride is the distillate C The distillate is water D Seawater is a pure substance

Show worked solution

Correct answer: C

Reasoning: Filtration removes insoluble sand, while distillation vaporizes and condenses water away from dissolved salts. Therefore option C is correct.

QUESTION 31 [1 mark]

Multiple choice Standard No calculator About 2 min

A heating curve for ethanol contains plateaus near $-114\,^{\circ}\mathrm{C}$ and $78\,^{\circ}\mathrm{C}$. What occurs at the higher plateau during heating?

A Freezing B Boiling C Deposition D Sublimation

Show worked solution

Correct answer: B

Reasoning: At ethanol’s normal boiling point, supplied energy overcomes intermolecular attractions while temperature remains constant. Therefore option B is correct.

QUESTION 32 [6 marks]

Multi-part Standard No calculator About 9 min

A mixture contains iron filings, sand, sodium chloride and water. Give a sequence that recovers each solid and produces pure water.

Show worked solution

Use a magnet to remove iron. Filter to separate sand from the salt solution, then wash and dry the sand. Distil the filtrate to collect pure water as distillate; evaporate or crystallize the concentrated residue to recover sodium chloride.

Final answer: Magnetic separation, filtration, distillation and crystallization in a valid sequence.

QUESTION 33 [1 mark]

Multiple choice Standard No calculator About 2 min

Balance $\mathrm{Al_2O_3+NaOH+H_2O\to NaAl(OH)_4}$. What is the coefficient sum?

A 5 B 6 C 7 D 8

Show worked solution

Correct answer: D

Reasoning: Coefficients 1, 2, 3 and 2 balance the equation; the sum is 8. Therefore option D is correct.

QUESTION 34 [1 mark]

Multiple choice Standard No calculator About 2 min

Which change is condensation?

A Br$_2$(l) → Br$_2$(g) B H$_2$O(g) → H$_2$O(l) C CO$_2$(s) → CO$_2$(g) D NaOH + HCl → NaCl + H$_2$O

Show worked solution

Correct answer: B

Reasoning: Condensation is the phase change from gas to liquid. Therefore option B is correct.

QUESTION 35 [1 mark]

Multiple choice Standard No calculator About 2 min

Balance $NO_2+H_2O\to HNO_3+NO$. What is the coefficient sum?

A 6 B 7 C 8 D 9

Show worked solution

Correct answer: B

Reasoning: The balanced equation is $3NO_2+H_2O\to2HNO_3+NO$, whose coefficients sum to 7. Therefore option B is correct.

QUESTION 36 [1 mark]

Multiple choice Standard No calculator About 2 min

For pure substances and mixtures, which statements are correct: I every pure substance is an element; II a pure substance has a sharp melting point; III a heterogeneous mixture contains more than one substance?

A I only B I and II only C II and III only D II only

Show worked solution

Correct answer: C

Reasoning: Pure compounds exist, so I is false. A pure material has a characteristic sharp melting point, and a heterogeneous mixture has multiple substances. Therefore option C is correct.