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VCE Chemistry practice questions

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Question 1Units 1 and 2

Which particle is found in the nucleus of an atom and carries no electrical charge?

  1. Neutron Correct answer.
  2. Positron
  3. Proton
  4. Electron

Explanation

The nucleus contains protons and neutrons. A proton carries a positive charge and an electron carries a negative charge, so the electrically neutral nuclear particle is the neutron. Its mass is close to that of a proton.

Question 2Units 1 and 2

An atom of an element has the electron configuration 2,8,7. In which group of the periodic table does this element belong?

  1. Group 15
  2. Group 7
  3. Group 3
  4. Group 17 Correct answer.

Explanation

For main-group elements the group number is found from the number of valence electrons. This atom has seven electrons in its outer shell, which places it in Group 17, the halogens. Group 7 is a transition-metal group with a different electron pattern.

Question 3Units 1 and 2

Which statement best describes an isotope of an element?

  1. An atom with a different number of protons but the same number of neutrons
  2. An atom with the same number of protons but a different number of neutrons Correct answer.
  3. An ion formed when an atom loses or gains one or more electrons
  4. An atom with the same number of neutrons but a different number of electrons

Explanation

Isotopes are atoms of the same element, so they share the same atomic number and proton count. They differ only in neutron number, which changes the mass number. Changing proton number would create a different element, and changing electron number creates an ion.

Question 4Units 1 and 2

A sample of magnesium consists of 79.0% of atoms with mass number 24 and 21.0% of atoms with mass number 25. What is the relative atomic mass of this sample, to three significant figures?

  1. 24.2 Correct answer.
  2. 25.0
  3. 24.5
  4. 24.0

Explanation

Relative atomic mass is the weighted average of isotope masses using their abundances. Calculating (0.790 x 24) + (0.210 x 25) gives 18.96 + 5.25 = 24.21, which rounds to 24.2. The value must lie between the two isotope masses.

Question 5Units 1 and 2

Which species contains 18 electrons?

  1. Ne
  2. Na+
  3. Mg2+
  4. Cl- Correct answer.

Explanation

A chlorine atom has 17 electrons, and gaining one electron gives the chloride ion 18 electrons. Sodium and magnesium ions lose electrons and end up with fewer than 18, while a neon atom has only 10.

Question 6Units 1 and 2

Which type of bonding is present in solid sodium chloride?

  1. Covalent bonding
  2. Metallic bonding
  3. Hydrogen bonding
  4. Ionic bonding Correct answer.

Explanation

Sodium chloride is formed from a metal cation and a non-metal anion. Electrons are transferred from sodium to chlorine, and the resulting oppositely charged ions are held in a lattice by electrostatic attraction, which is ionic bonding.

Question 7Units 1 and 2

Which property is characteristic of a covalent molecular substance such as water?

  1. It conducts electricity when solid.
  2. It has a very high melting point.
  3. It forms a lattice of ions.
  4. It has a low melting point. Correct answer.

Explanation

Molecular covalent substances are held together internally by strong covalent bonds but between molecules only by weak intermolecular forces. Melting requires breaking only these weak forces, so melting points are low. They do not conduct electricity because they contain no free ions or electrons.

Question 8Units 1 and 2

Which substance is a giant covalent network solid?

  1. Sodium chloride
  2. Iodine
  3. Diamond Correct answer.
  4. Copper

Explanation

Diamond consists of carbon atoms each covalently bonded to four neighbours in an extended three-dimensional network. This giant covalent structure gives diamond its very high melting point and hardness. The other substances are ionic, molecular or metallic respectively.

Question 9Units 1 and 2

Which statement correctly explains why metals conduct electricity?

  1. Metal atoms contain protons that move between lattice sites.
  2. Delocalised electrons are free to move through the metal lattice. Correct answer.
  3. Metal ions vibrate and carry charge through the lattice.
  4. Metal atoms transfer electrons to form ions that move freely.

Explanation

In a metal lattice, valence electrons are not localised to individual atoms but form a sea of delocalised electrons. When a potential difference is applied these electrons drift through the structure, carrying charge. The positive metal ions stay fixed in position.

Question 10Units 1 and 2

Which intermolecular force is the strongest for a sample of liquid water?

  1. Ion-dipole attraction
  2. Dispersion forces only
  3. Dipole-dipole attraction only
  4. Hydrogen bonding Correct answer.

Explanation

Water molecules have O-H bonds with hydrogen attached to a highly electronegative atom, so extensive hydrogen bonding occurs between molecules. Hydrogen bonds are stronger than ordinary dipole-dipole attractions and dispersion forces. Ion-dipole attractions require ions, which pure water does not contain.

Question 11Units 1 and 2

Which pair of substances is most likely to dissolve in each other?

  1. Hexane and water
  2. Iodine and water
  3. Sodium chloride and hexane
  4. Ethanol and water Correct answer.

Explanation

The general rule is that like dissolves like, so polar solutes dissolve in polar solvents. Ethanol and water are both polar and can hydrogen bond with each other, so they mix readily. Non-polar substances such as hexane and iodine do not dissolve well in water.

Question 12Units 1 and 2

Which change in conditions increases the rate of a chemical reaction between two gases?

  1. Increasing the volume of the container
  2. Decreasing the pressure
  3. Decreasing the temperature
  4. Increasing the concentration of a reactant Correct answer.

Explanation

Reaction rate increases when reactant particles collide more frequently with sufficient energy. Raising the concentration of a reactant increases the number of particles per unit volume, so collision frequency rises. Lowering temperature or pressure reduces collision frequency.

Question 13Units 1 and 2

What is the effect of adding a catalyst to a reaction?

  1. It increases the energy of the products relative to the reactants.
  2. It lowers the activation energy without being consumed overall. Correct answer.
  3. It changes the enthalpy change of the reaction.
  4. It increases the activation energy and is consumed.

Explanation

A catalyst provides an alternative reaction pathway with a lower activation energy, so a larger proportion of collisions are successful. The catalyst is regenerated and not used up overall. It does not alter the enthalpy change, which depends only on reactants and products.

Question 14Units 1 and 2

Which observation best indicates that a chemical reaction has occurred?

  1. A solid is crushed into a fine powder.
  2. A solid dissolves in water to form a clear solution.
  3. A liquid changes colour slightly when warmed.
  4. A gas is produced when two solutions are mixed. Correct answer.

Explanation

Formation of a new gas from the mixing of two solutions indicates a new substance has been produced, which is evidence of a chemical change. Dissolving, thermal colour shifts and crushing are physical processes that do not necessarily create new substances.

Question 15Units 1 and 2

Which equation represents a balanced combustion reaction of methane?

  1. CH4 + 2O2 -> CO2 + 2H2O Correct answer.
  2. CH4 + O2 -> CO2 + H2O
  3. 2CH4 + O2 -> 2CO2 + H2O
  4. CH4 + O2 -> CO + H2O

Explanation

A balanced equation must have equal numbers of each type of atom on both sides. In option B there are one carbon, four hydrogen and four oxygen atoms on each side. The other equations have unequal atom counts or represent incomplete combustion.

Question 16Units 1 and 2

In the reaction 2H2 + O2 -> 2H2O, how many moles of water are produced when 0.50 mol of O2 reacts completely?

  1. 0.25 mol
  2. 0.50 mol
  3. 2.0 mol
  4. 1.0 mol Correct answer.

Explanation

The balanced equation shows a mole ratio of 1 mol O2 to 2 mol H2O. Therefore 0.50 mol of oxygen produces 0.50 x 2 = 1.0 mol of water. The hydrogen must be in excess for oxygen to react completely.

Question 17Units 1 and 2

What is the molar mass of carbon dioxide, CO2? (C = 12.0, O = 16.0)

  1. 28.0 g/mol
  2. 44.0 g/mol Correct answer.
  3. 12.0 g/mol
  4. 32.0 g/mol

Explanation

Molar mass is the sum of the atomic masses of all atoms in the formula. Carbon dioxide contains one carbon (12.0) and two oxygens (2 x 16.0 = 32.0), giving 44.0 g/mol.

Question 18Units 1 and 2

A solution contains 0.20 mol of sodium hydroxide dissolved to make 500 mL of solution. What is the concentration of the solution?

  1. 0.40 mol/L Correct answer.
  2. 2.0 mol/L
  3. 0.20 mol/L
  4. 0.10 mol/L

Explanation

Concentration equals amount in moles divided by volume in litres. Here 0.20 mol divided by 0.500 L gives 0.40 mol/L. Note that 500 mL must be converted to 0.500 L before dividing.

Question 19Units 1 and 2

Which gas would be produced at the cathode during the electrolysis of molten sodium chloride?

  1. Oxygen
  2. Sodium Correct answer.
  3. Chlorine
  4. Hydrogen

Explanation

In molten sodium chloride the ions present are Na+ and Cl-. Reduction occurs at the cathode, where Na+ ions gain electrons to form sodium metal. Chlorine forms at the anode through oxidation of chloride ions.

Question 20Units 1 and 2

Which species is oxidised in the reaction Zn + Cu2+ -> Zn2+ + Cu?

  1. Zn Correct answer.
  2. Cu
  3. Cu2+
  4. Zn2+

Explanation

Oxidation is loss of electrons, shown by an increase in oxidation number. Zinc changes from oxidation number 0 to +2, so it loses electrons and is oxidised. The copper ion gains those electrons and is reduced.

Question 21Units 1 and 2

Which statement about an exothermic reaction is correct?

  1. The reaction cannot occur without a continuous energy supply.
  2. The products have more enthalpy than the reactants and energy is absorbed.
  3. The activation energy is always zero.
  4. The products have less enthalpy than the reactants and energy is released. Correct answer.

Explanation

In an exothermic reaction the enthalpy of the products is lower than that of the reactants, so the excess energy is released to the surroundings, usually as heat. The activation energy is still required to start the reaction, but it is not zero.

Question 22Units 1 and 2

Which quantity is conserved in every chemical reaction?

  1. Volume of gas
  2. Total mass Correct answer.
  3. Number of moles of gas
  4. Number of molecules

Explanation

The law of conservation of mass states that matter is neither created nor destroyed in a chemical reaction. The total mass of reactants therefore equals the total mass of products. Numbers of molecules and gas volumes can change as atoms are rearranged.

Question 23Units 1 and 2

A student measures the pH of four solutions. Which solution is the most acidic?

  1. pH 5
  2. pH 2 Correct answer.
  3. pH 9
  4. pH 7

Explanation

pH is a logarithmic scale on which lower values indicate higher hydrogen ion concentration and greater acidity. A pH of 2 corresponds to a hydrogen ion concentration of 0.01 mol/L, the highest of the four. A pH of 7 is neutral and pH 9 is basic.

Question 24Units 1 and 2

A weak acid is titrated with a strong base. Which statement best describes the acid?

  1. It ionises only partially in water, so an equilibrium exists between ionised and un-ionised forms. Correct answer.
  2. It reacts with water to release hydroxide ions.
  3. It ionises completely in water and has a large acid dissociation constant.
  4. It produces no hydrogen ions at all in solution.

Explanation

A weak acid only partially ionises in water, establishing an equilibrium between the intact acid molecules and the ions formed. Its acid dissociation constant is small. Strong acids, by contrast, ionise essentially completely.

Question 25Units 1 and 2

Which observation would indicate that a precipitate has formed when two clear solutions are mixed?

  1. The mixture becomes warmer.
  2. A gas bubbles out of the mixture.
  3. The mixture becomes more transparent.
  4. A solid appears in the mixture. Correct answer.

Explanation

A precipitate is an insoluble solid that forms when ions in two solutions combine to produce an insoluble compound. Its appearance is therefore seen as a solid forming in the mixture. Warming or gas evolution indicates other processes.

Question 26Units 1 and 2

Which particle is transferred when a sodium atom forms a sodium ion, Na⁺?

  1. One neutron is lost
  2. One electron is lost Correct answer.
  3. One electron is gained
  4. One proton is lost

Explanation

Metal atoms such as sodium achieve a stable electron configuration by losing their single valence electron, giving a positive charge of 1+. The nucleus is unchanged in ordinary chemical reactions, so proton number stays the same.

Question 27Units 1 and 2

An element has the electron configuration 2,8,7. In which group and period of the periodic table is it found?

  1. Group 17, Period 2
  2. Group 7, Period 3 Correct answer.
  3. Group 15, Period 3
  4. Group 2, Period 7

Explanation

The number of occupied shells (three) gives the period, and the number of outer-shell electrons (seven) gives the group number in the main-group shorthand. So the element sits in Group 7 (also numbered 17) and Period 3.

Question 28Units 1 and 2

Which description correctly matches the trend in first ionisation energy across Period 3 from sodium to argon?

  1. It generally increases because the number of shells increases
  2. It generally decreases because atomic radius increases
  3. It stays constant because the outer shell stays the same
  4. It generally increases because nuclear charge rises while shielding stays similar Correct answer.

Explanation

Across a period, protons are added while electrons enter the same shell, so effective nuclear charge increases and the outer electron is held more tightly. This raises ionisation energy overall, though small dips occur at aluminium and sulfur.

Question 29Units 1 and 2

Which formula is correct for the ionic compound formed between aluminium ions and oxide ions?

  1. Al₂O₃ Correct answer.
  2. AlO
  3. AlO₂
  4. Al₃O₂

Explanation

Aluminium forms Al³⁺ and oxygen forms O²⁻; charges must balance overall, so two Al³⁺ (total +6) pair with three O²⁻ (total −6). The empirical formula is therefore Al₂O₃.

Question 30Units 1 and 2

Which statement best explains why graphite is softer and more slippery than diamond, even though both are carbon networks?

  1. Graphite has fewer covalent bonds per carbon atom than diamond
  2. Graphite has a lower melting point because it contains ions
  3. Graphite contains weaker covalent bonds within its layers
  4. Graphite layers are held by weak dispersion forces that allow them to slide Correct answer.

Explanation

In graphite each carbon is covalently bonded to three others in a layer, and the layers are stacked and held only by weak dispersion forces. These forces allow layers to slide past one another, giving the soft, lubricating feel.

Question 31Units 1 and 2

A sample of gas occupies 250 mL at 100 kPa. Assuming constant temperature, what volume does it occupy at 200 kPa?

  1. 500 mL
  2. 250 mL
  3. 1000 mL
  4. 125 mL Correct answer.

Explanation

Boyle's law states that pressure and volume are inversely proportional at constant temperature, so P₁V₁ = P₂V₂. Doubling the pressure halves the volume: 250 mL × (100/200) = 125 mL.

Question 32Units 1 and 2

A sealed rigid container holds 0.50 mol of gas at 300 K. If the temperature is raised to 600 K, what happens to the pressure?

  1. It quadruples
  2. It halves
  3. It doubles Correct answer.
  4. It stays the same

Explanation

At fixed volume and amount of gas, pressure is directly proportional to absolute temperature (Gay-Lussac's law). Doubling the kelvin temperature from 300 K to 600 K therefore doubles the pressure.

Question 33Units 1 and 2

Which statement correctly describes what happens to the particles of a solid as it melts?

  1. Chemical bonds within each molecule are broken to form new substances
  2. Particles lose energy and become fixed in a rigid lattice
  3. Particles gain energy and the regular lattice breaks down while particles stay close together Correct answer.
  4. Particles gain enough energy to move far apart and fill the container

Explanation

Melting supplies energy that overcomes the forces holding particles in their lattice positions, so particles can move past one another. They remain close together in the liquid, so the arrangement changes but the substance does not.

Question 34Units 1 and 2

A compound contains 40.0% carbon, 6.7% hydrogen and 53.3% oxygen by mass. What is its empirical formula? (C = 12.0, H = 1.0, O = 16.0)

  1. C₂H₆O
  2. C₂H₄O₂
  3. CHO
  4. CH₂O Correct answer.

Explanation

Dividing each percentage by its molar mass gives mole ratios of 3.33 C, 6.7 H and 3.33 O. Dividing by the smallest value gives 1:2:1, so the empirical formula is CH₂O.

Question 35Units 1 and 2

What is the percentage by mass of nitrogen in ammonium sulfate, (NH₄)₂SO₄? (N = 14.0, H = 1.0, S = 32.0, O = 16.0)

  1. 21.2% Correct answer.
  2. 28.0%
  3. 14.0%
  4. 10.6%

Explanation

The molar mass is 2(14.0) + 8(1.0) + 32.0 + 4(16.0) = 132 g/mol, and the nitrogen contributes 28.0 g/mol. Dividing 28.0 by 132 and multiplying by 100 gives about 21.2%.

Question 36Units 1 and 2

In the reaction N₂(g) + 3H₂(g) → 2NH₃(g), what volume of hydrogen at the same temperature and pressure reacts completely with 2.0 L of nitrogen?

  1. 6.0 L Correct answer.
  2. 4.0 L
  3. 1.0 L
  4. 2.0 L

Explanation

Avogadro's law means gas volumes react in the same ratio as the coefficients in the balanced equation. The equation requires three volumes of hydrogen for each volume of nitrogen, so 2.0 L of nitrogen needs 6.0 L of hydrogen.

Question 37Units 1 and 2

Which change would shift the equilibrium N₂O₄(g) ⇌ 2NO₂(g) (endothermic in the forward direction) towards more NO₂?

  1. Increasing the total pressure
  2. Raising the temperature Correct answer.
  3. Lowering the temperature
  4. Adding a catalyst

Explanation

Le Chatelier's principle predicts that heating favours the endothermic direction, which here is the forward reaction producing NO₂. The system absorbs the added thermal energy by shifting to the right.

Question 38Units 1 and 2

A reversible reaction reaches equilibrium in a closed container. Which statement about the system at equilibrium is correct?

  1. The total amount of products is at its maximum possible value
  2. The forward reaction has stopped while the reverse reaction continues
  3. The forward and reverse reaction rates are equal and concentrations stay constant Correct answer.
  4. The concentrations of reactants and products are equal

Explanation

At dynamic equilibrium both directions continue at equal rates, so the amounts of each substance remain constant even though reactions are still occurring. Concentrations are constant but not necessarily equal.

Question 39Units 1 and 2

Which factor increases the rate of reaction between marble chips and dilute hydrochloric acid?

  1. Diluting the acid with water
  2. Cooling the reaction mixture
  3. Using larger chips of the same total mass
  4. Using powdered marble instead of chips of the same mass Correct answer.

Explanation

Powdered marble has a much greater surface area exposed to the acid, so more collisions occur per unit time and the reaction is faster. The amount of marble is unchanged, so the same total gas is eventually produced.

Question 40Units 1 and 2

A reaction is found to release 450 J of energy to the surroundings. Which statement about its enthalpy change is correct?

  1. ΔH = −450 J, and the products have more enthalpy than the reactants
  2. ΔH = +450 J, and the surroundings lose energy
  3. ΔH = −450 J, and the products have less enthalpy than the reactants Correct answer.
  4. ΔH = +450 J, and the products have more enthalpy than the reactants

Explanation

By convention, energy released to the surroundings gives a negative enthalpy change for the system. The products therefore contain less chemical enthalpy than the reactants, the difference being lost as heat.

Question 41Units 1 and 2

Which equation represents the correct ionic equation for the reaction between hydrochloric acid and sodium hydroxide solution?

  1. HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)
  2. Na⁺(aq) + Cl⁻(aq) → NaCl(aq)
  3. H⁺(aq) + Cl⁻(aq) → HCl(aq)
  4. H⁺(aq) + OH⁻(aq) → H₂O(l) Correct answer.

Explanation

Both the acid and the base are strong electrolytes, so the only species that actually change are hydrogen and hydroxide ions. Their combination to form water is the net ionic equation, with sodium and chloride as spectator ions.

Question 42Units 1 and 2

A solution has a hydrogen ion concentration of 1 × 10⁻³ mol/L. What is its pH?

  1. 11
  2. 1 × 10⁻³
  3. 3 Correct answer.
  4. −3

Explanation

pH is defined as the negative base-10 logarithm of the hydrogen ion concentration. For [H⁺] = 1 × 10⁻³ mol/L, pH = −log(10⁻³) = 3.

Question 43Units 1 and 2

Which property of water is best explained by hydrogen bonding between its molecules?

  1. Its low molar mass
  2. Its ability to dissolve non-polar oils
  3. Its lack of reactivity with sodium
  4. Its unusually high boiling point compared with similar-sized molecules Correct answer.

Explanation

Hydrogen bonds between water molecules are much stronger than the dispersion forces between molecules of similar molar mass. Extra energy is therefore needed to separate molecules, giving water an unusually high boiling point.

Question 44Units 1 and 2

Which species acts as the reducing agent in the reaction Fe + CuSO₄ → FeSO₄ + Cu?

  1. Cu²⁺
  2. SO₄²⁻
  3. Cu
  4. Fe Correct answer.

Explanation

Iron loses electrons and is oxidised to Fe²⁺, so it is the species that brings about the reduction of Cu²⁺. The reducing agent is therefore the species being oxidised.

Question 45Units 1 and 2

Which half-equation correctly represents the oxidation process?

  1. Fe²⁺ → Fe³⁺ + e⁻ Correct answer.
  2. Cu²⁺ + 2e⁻ → Cu
  3. Cl₂ + 2e⁻ → 2Cl⁻
  4. Fe³⁺ + e⁻ → Fe²⁺

Explanation

Oxidation is loss of electrons, shown as electrons appearing on the product side. Converting Fe²⁺ to Fe³⁺ releases one electron, so this half-equation represents oxidation.

Question 46Units 1 and 2

During the electrolysis of copper(II) sulfate solution using inert electrodes, which change occurs at the anode?

  1. Water is oxidised to oxygen gas and hydrogen ions Correct answer.
  2. Hydroxide ions are reduced to hydrogen gas
  3. Copper ions gain electrons to form a deposit
  4. Copper ions are reduced to copper metal

Explanation

At the anode, oxidation occurs; with inert electrodes the sulfate ion is not readily oxidised, so water molecules lose electrons to form oxygen and hydrogen ions. Copper is deposited at the cathode by reduction instead.

Question 47Units 1 and 2

Which statement correctly describes how a galvanic cell produces electrical energy?

  1. Positive ions move through the external wire to complete the circuit
  2. Electrons travel through the electrolyte from cathode to anode
  3. A spontaneous redox reaction drives electrons through the external circuit from anode to cathode Correct answer.
  4. An external power supply forces a non-spontaneous reaction to occur

Explanation

In a galvanic cell, oxidation at the anode releases electrons that travel through the external circuit to the cathode, where reduction occurs. The cell converts chemical energy into electrical energy spontaneously.

Question 48Units 1 and 2

Which substance is a strong electrolyte when dissolved in water?

  1. Glucose
  2. Potassium nitrate Correct answer.
  3. Acetic acid
  4. Ethanol

Explanation

Potassium nitrate is an ionic compound that dissociates completely into ions in water, so the solution conducts electricity well. Strong electrolytes ionise or dissociate fully, unlike weak acids or molecular solutes.

Question 49Units 1 and 2

A student adds excess magnesium ribbon to 100 mL of 0.50 mol/L hydrochloric acid. What volume of hydrogen gas, measured at standard conditions where one mole of gas occupies 24.5 L, is produced?

  1. 1.23 L
  2. 0.31 L
  3. 2.45 L
  4. 0.61 L Correct answer.

Explanation

Moles of HCl = 0.100 L × 0.50 mol/L = 0.050 mol. From Mg + 2HCl → MgCl₂ + H₂, hydrogen moles are half of this, 0.025 mol, and 0.025 × 24.5 L/mol ≈ 0.61 L.

Question 50Units 1 and 2

Which statement correctly distinguishes a saturated solution from a concentrated solution?

  1. A saturated solution cannot be made from a gas dissolved in water
  2. A concentrated solution always contains undissolved solute
  3. A saturated solution always contains a large mass of dissolved solute
  4. A saturated solution contains the maximum solute that can dissolve at that temperature, which may still be dilute Correct answer.

Explanation

Saturation depends on how much solute the solvent can hold at a given temperature, not on the absolute amount dissolved. A saturated solution of a sparingly soluble salt can therefore be quite dilute.