I85PREP
⌘ K
NCEA L2 Chemistry study materials
NCEA L2 Chemistry study resources

NCEA L2 Chemistry practice questions

One question at a time. Build your NCEA L2 Chemistry understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which particle arrangement best describes the structure of a solid ionic compound such as sodium chloride at room temperature?

  1. Discrete molecules each containing one sodium ion covalently bonded to one chloride ion
  2. A regular three-dimensional lattice of alternating cations and anions held by electrostatic attraction Correct answer.
  3. Randomly arranged ions that are free to move throughout the solid
  4. A sea of delocalised electrons surrounding a lattice of positive ions

Explanation

Ionic solids consist of oppositely charged ions packed into a repeating three-dimensional lattice, and the strong electrostatic attraction between these ions holds the structure together. There are no discrete molecules in an ionic lattice, and the ions are not free to move in the solid state.

Question 2Chemistry achievement standards (Level 2) - content domains not enumerated in source

A covalent bond between two atoms is best described as the result of which interaction?

  1. The sharing of protons between the nuclei of the two atoms
  2. The electrostatic attraction between a shared pair of electrons and the two nuclei Correct answer.
  3. The attraction between temporary dipoles formed in neighbouring molecules
  4. The transfer of one or more electrons from one atom to another

Explanation

A covalent bond forms when two atoms share one or more pairs of electrons, and the bond strength comes from the attraction of both nuclei to that shared electron density. Electron transfer instead produces ions and ionic bonding.

Question 3Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which statement correctly describes the trend in atomic radius across Period 3 from sodium to chlorine?

  1. The radius increases because more electron shells are added
  2. The radius stays constant because the number of shells does not change
  3. The radius increases because the atoms gain electrons and become anions
  4. The radius decreases because the nuclear charge increases while electrons are added to the same shell Correct answer.

Explanation

Across a period, protons are added to the nucleus while electrons enter the same outer shell, so the effective nuclear charge rises and pulls the electron cloud closer. This causes the atomic radius to decrease from left to right.

Question 4Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which balanced equation represents the complete combustion of ethane, C2H6?

  1. C2H6 + 2O2 → 2CO + 2H2O
  2. 2C2H6 + 7O2 → 4CO2 + 6H2O Correct answer.
  3. C2H6 + O2 → C2H4 + H2O
  4. C2H6 + 3O2 → 2CO2 + 3H2O

Explanation

Complete combustion of a hydrocarbon gives carbon dioxide and water. Balancing two C2H6 molecules requires 4 carbon atoms (4CO2) and 12 hydrogen atoms (6H2O), which needs 14 oxygen atoms, or 7O2.

Question 5Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which pair of species is isoelectronic with the neon atom?

  1. Mg2+ and K+
  2. O2− and S2−
  3. Na+ and Cl−
  4. Na+ and F− Correct answer.

Explanation

Neon has 10 electrons. Na+ has lost one electron from 11 to give 10, and F− has gained one to give 10, so both are isoelectronic with neon.

Question 6Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which type of intermolecular force is primarily responsible for the relatively high boiling point of water compared with hydrogen sulfide, H2S?

  1. London dispersion forces
  2. Hydrogen bonding Correct answer.
  3. Ionic attraction between molecules
  4. Dipole–dipole attractions

Explanation

Water molecules form hydrogen bonds because hydrogen is bonded to a highly electronegative oxygen atom, and these strong intermolecular forces require considerable energy to overcome. H2S has weaker dipole and dispersion forces because sulfur is less electronegative and larger.

Question 7Chemistry achievement standards (Level 2) - content domains not enumerated in source

In the reaction Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s), which species is oxidised?

  1. Cu2+(aq)
  2. Cu(s)
  3. Zn2+(aq)
  4. Zn(s) Correct answer.

Explanation

Oxidation is loss of electrons. Zinc starts as a neutral atom and becomes Zn2+, losing two electrons, so zinc is oxidised while copper ions gain those electrons and are reduced.

Question 8Chemistry achievement standards (Level 2) - content domains not enumerated in source

What is the molar mass of hydrated copper sulfate, CuSO4·5H2O? Use Ar: Cu = 63.5, S = 32.0, O = 16.0, H = 1.0.

  1. 177.5 g mol−1
  2. 267.5 g mol−1
  3. 159.5 g mol−1
  4. 249.5 g mol−1 Correct answer.

Explanation

The formula mass is 63.5 + 32.0 + (4 × 16.0) = 159.5 for CuSO4, plus 5 × (2.0 + 16.0) = 90.0 for the water of crystallisation. Adding these gives 249.5 g mol−1.

Question 9Chemistry achievement standards (Level 2) - content domains not enumerated in source

A student dissolves 4.0 g of sodium hydroxide (Mr = 40.0) in water and makes the solution up to 500 mL. What is the concentration of the solution?

  1. 0.50 mol L−1
  2. 0.20 mol L−1 Correct answer.
  3. 2.0 mol L−1
  4. 0.10 mol L−1

Explanation

The amount of NaOH is 4.0 g ÷ 40.0 g mol−1 = 0.10 mol, and the volume is 0.500 L. Dividing 0.10 mol by 0.500 L gives 0.20 mol L−1.

Question 10Chemistry achievement standards (Level 2) - content domains not enumerated in source

25.0 mL of 0.100 mol L−1 HCl is exactly neutralised by 20.0 mL of NaOH solution. What is the concentration of the NaOH?

  1. 0.125 mol L−1 Correct answer.
  2. 0.0800 mol L−1
  3. 0.200 mol L−1
  4. 0.100 mol L−1

Explanation

HCl and NaOH react in a 1:1 ratio, so moles of HCl = 0.0250 L × 0.100 mol L−1 = 2.50 × 10−3 mol. This equals the moles of NaOH, and dividing by 0.0200 L gives 0.125 mol L−1.

Question 11Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which change would shift the equilibrium of the exothermic reaction N2(g) + 3H2(g) ⇌ 2NH3(g) towards the products?

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

Explanation

There are four gas moles on the left and two on the right, so increasing pressure favours the side with fewer gas molecules, the products. Le Chatelier's principle predicts the system shifts to reduce the pressure change.

Question 12Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which factor increases the rate of a reaction between marble chips and hydrochloric acid without changing the amount of products formed?

  1. Cooling the acid
  2. Increasing the volume of acid while keeping its concentration the same
  3. Grinding the marble into a fine powder Correct answer.
  4. Diluting the acid with water

Explanation

Grinding the solid increases its surface area, giving more frequent collisions between acid particles and the solid surface, so the rate increases. The total amount of marble is unchanged, so the final amount of product is the same.

Question 13Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which statement correctly explains why the melting point of magnesium oxide is much higher than that of sodium chloride?

  1. MgO contains mobile electrons that conduct heat and raise the melting point
  2. MgO contains covalent bonds while NaCl contains ionic bonds
  3. MgO has ions of higher charge (2+ and 2−) giving stronger electrostatic attraction than the 1+ and 1− ions in NaCl Correct answer.
  4. MgO has a smaller lattice with fewer ions per unit cell, so it melts more easily

Explanation

Both compounds are ionic, but MgO is built from Mg2+ and O2− ions while NaCl contains Na+ and Cl− ions. The higher ionic charges in MgO produce much stronger electrostatic attraction throughout the lattice, so more energy is needed to melt it.

Question 14Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which molecule has a trigonal pyramidal shape?

  1. CH4
  2. CO2
  3. BF3
  4. NH3 Correct answer.

Explanation

Ammonia has three bonding pairs and one lone pair on nitrogen, giving four electron regions but a trigonal pyramidal molecular shape. The lone pair occupies more space, so the H–N–H angles are slightly less than 109.5°.

Question 15Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which substance is a weak acid when dissolved in water?

  1. HCl
  2. HNO3
  3. CH3COOH Correct answer.
  4. H2SO4

Explanation

Ethanoic acid only partially ionises in water, so it is a weak acid and establishes an equilibrium with few ions present. Hydrochloric, nitric and sulfuric acids ionise essentially completely and are strong acids.

Question 16Chemistry achievement standards (Level 2) - content domains not enumerated in source

What is the pH of a solution with a hydrogen ion concentration of 1 × 10−3 mol L−1?

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

Explanation

pH is defined as −log10[H+]. For [H+] = 1 × 10−3 mol L−1, the logarithm is −3, so the pH is 3, which is acidic as expected.

Question 17Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which observation would indicate that a redox reaction has occurred when an iron nail is placed in copper sulfate solution?

  1. The nail dissolves completely with no change in solution colour
  2. The blue colour of the solution intensifies and the nail becomes thicker
  3. A reddish-brown deposit forms on the nail and the blue colour fades Correct answer.
  4. Bubbles of hydrogen gas are produced at the nail

Explanation

Iron is more reactive than copper, so it displaces copper ions from solution: Fe(s) + Cu2+(aq) → Fe2+(aq) + Cu(s). The copper metal appears as a reddish-brown coating and the blue Cu2+ colour fades as the ions are reduced.

Question 18Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which statement best explains why the noble gases have very high ionisation energies?

  1. They have full outer electron shells, so removing an electron means breaking a stable, low-energy configuration Correct answer.
  2. They have very large atomic radii, so the outer electrons are strongly attracted
  3. They form strong covalent bonds that must be broken before ionisation
  4. They have only one electron in their outer shell, which is easily removed

Explanation

Noble gases have complete outer shells, a particularly stable arrangement, so the outer electrons are held firmly and removing one requires a large amount of energy. This accounts for their very high ionisation energies.

Question 19Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which species has the electron configuration 1s2 2s2 2p6 3s2 3p6?

  1. Ne
  2. K+
  3. Na+
  4. Cl− Correct answer.

Explanation

The configuration shown contains 18 electrons, matching the argon arrangement. Chlorine has 17 electrons, so the chloride ion Cl− has gained one electron and has 18, giving this configuration.

Question 20Chemistry achievement standards (Level 2) - content domains not enumerated in source

A sample of an unknown hydrocarbon is burned completely and produces 8.8 g of CO2 and 3.6 g of H2O. What is the empirical formula? Use Ar: C = 12.0, H = 1.0, O = 16.0.

  1. C3H8
  2. CH2 Correct answer.
  3. C2H6
  4. CH4

Explanation

Moles of CO2 = 8.8 ÷ 44.0 = 0.20 mol, so there are 0.20 mol of carbon. Moles of H2O = 3.6 ÷ 18.0 = 0.20 mol, giving 0.40 mol of hydrogen. The ratio C:H is 0.20:0.40 = 1:2, so the empirical formula is CH2.

Question 21Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which pair of solutions would, when mixed, produce a precipitate of barium sulfate?

  1. Barium chloride and sodium chloride
  2. Barium nitrate and potassium nitrate
  3. Barium chloride and sodium sulfate Correct answer.
  4. Sodium sulfate and potassium chloride

Explanation

A precipitate forms when two soluble solutions react to produce an insoluble salt. Barium chloride provides Ba2+ and sodium sulfate provides SO42−, and barium sulfate is insoluble, so it precipitates.

Question 22Chemistry achievement standards (Level 2) - content domains not enumerated in source

Consider the equilibrium 2SO2(g) + O2(g) ⇌ 2SO3(g), which is exothermic in the forward direction. Which change would increase the equilibrium yield of SO3?

  1. Raising the temperature and adding a catalyst
  2. Lowering the temperature and decreasing the pressure
  3. Lowering the temperature and increasing the pressure Correct answer.
  4. Raising the temperature and increasing the volume

Explanation

Lowering the temperature favours the exothermic forward reaction, increasing SO3. Increasing pressure favours the side with fewer gas molecules (two on the right versus three on the left), which also increases SO3.

Question 23Chemistry achievement standards (Level 2) - content domains not enumerated in source

A 0.10 mol L−1 solution of a weak monoprotic acid has a pH of 3.0. Which statement best describes the acid?

  1. It is weak because the solution contains no hydrogen ions
  2. It is a strong acid because the pH is below 7
  3. It is strong because the concentration and pH values differ by a factor of 10
  4. It is weak because only about 1% of the acid molecules have ionised Correct answer.

Explanation

For a 0.10 mol L−1 strong acid, [H+] would be 0.10 mol L−1 and the pH would be 1. A pH of 3 means [H+] = 1 × 10−3 mol L−1, so only about 1% of the acid has ionised, which is characteristic of a weak acid.

Question 24Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which statement correctly compares the strength of the intermolecular forces in the Group 17 elements F2, Cl2, Br2 and I2 as the group is descended?

  1. Dipole–dipole forces increase because the molecules become more polar
  2. Hydrogen bonding becomes stronger as the atoms get larger
  3. Covalent bond strength decreases, causing the molecules to break apart more easily
  4. London dispersion forces increase because the molecules have more electrons and are more polarisable Correct answer.

Explanation

The halogens are non-polar diatomic molecules, so their intermolecular forces are London dispersion forces. As the group is descended, the molecules have more electrons and are more polarisable, so dispersion forces strengthen and boiling points rise.

Question 25Chemistry achievement standards (Level 2) - content domains not enumerated in source

A student wants to prepare a pure dry sample of copper(II) sulfate crystals from copper(II) oxide and dilute sulfuric acid. Which procedure is most appropriate?

  1. Add excess acid to copper(II) oxide and evaporate the mixture to dryness
  2. Add a few drops of copper(II) oxide to the acid and evaporate the mixture to dryness
  3. Add excess copper(II) oxide to warm dilute sulfuric acid, filter off the excess solid, then crystallise the filtrate Correct answer.
  4. Add excess copper(II) oxide to the acid, then distil the mixture to collect the crystals

Explanation

Adding excess copper(II) oxide ensures all the acid reacts, and the unreacted solid is removed by filtration. The filtrate contains only copper(II) sulfate, which can then be crystallised to give pure crystals.

Question 26Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which electron configuration represents a neutral atom of an element in Group 2 of the periodic table?

  1. 1s2 2s2 2p6 3s2 3p6
  2. 1s2 2s2 2p6 3s2 Correct answer.
  3. 1s2 2s2 2p6 3s1
  4. 1s2 2s2 2p6 3s2 3p1

Explanation

Group 2 elements have two electrons in their outermost occupied shell. The configuration 1s2 2s2 2p6 3s2 ends in 3s2, giving two valence electrons and placing the element in Group 2.

Question 27Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which type of bonding holds the particles together in a crystal of solid potassium chloride?

  1. Ionic bonding between potassium cations and chloride anions Correct answer.
  2. Metallic bonding between positive ions in a sea of electrons
  3. Covalent bonding between potassium and chlorine atoms
  4. Hydrogen bonding between potassium and chlorine molecules

Explanation

Potassium chloride is formed from a metal and a non-metal, so electrons are transferred to give K+ and Cl− ions. The strong electrostatic attraction between these oppositely charged ions is ionic bonding.

Question 28Chemistry achievement standards (Level 2) - content domains not enumerated in source

A sample of gas occupies 150 mL at 300 K. Assuming constant pressure, what volume will it occupy at 400 K?

  1. 225 mL
  2. 200 mL Correct answer.
  3. 113 mL
  4. 150 mL

Explanation

At constant pressure, Charles's law gives V1/T1 = V2/T2, so V2 = 150 × 400/300 = 200 mL. Heating the gas increases its volume in direct proportion to the absolute temperature.

Question 29Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which species is the conjugate base of the hydrogencarbonate ion, HCO3−?

  1. CO2
  2. OH−
  3. CO32− Correct answer.
  4. H2CO3

Explanation

A conjugate base is formed when an acid loses one proton. Removing H+ from HCO3− leaves CO32−, so carbonate is the conjugate base.

Question 30Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which observation shows that a chemical change, rather than a physical change, has taken place?

  1. Ice melts to form liquid water at 0 °C
  2. Salt dissolves in water to give a clear solution
  3. A new gas is produced with a different smell from the reactants Correct answer.
  4. Ethanol evaporates from an open dish

Explanation

A chemical change produces new substances with different properties from the reactants, such as a gas with a new smell. The other changes involve only changes of state or dissolving, which are physical.

Question 31Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which ion is isoelectronic with the argon atom?

  1. Na+
  2. Mg2+
  3. Cl− Correct answer.
  4. K+

Explanation

The chloride ion has gained one electron, giving 18 electrons, the same number as argon. Argon has 18 electrons, so Cl− is isoelectronic with it.

Question 32Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which compound contains a carbon-carbon double bond?

  1. Ethanoic acid, CH3COOH
  2. Ethanol, C2H5OH
  3. Ethane, C2H6
  4. Ethene, C2H4 Correct answer.

Explanation

Ethene has the formula C2H4, so the two carbon atoms must share a double bond to satisfy the valency of four. The other compounds contain only single carbon-carbon bonds.

Question 33Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which change would increase the rate of a reaction between a solid and a solution?

  1. Using larger pieces of the solid
  2. Increasing the concentration of the solution Correct answer.
  3. Adding more solvent to dilute the solution
  4. Cooling the reaction mixture

Explanation

A higher concentration means more reactant particles per unit volume, so collisions occur more frequently and the rate increases. Cooling, using larger pieces or diluting all decrease the collision frequency.

Question 34Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which statement correctly describes the arrangement of particles in a solid ionic lattice?

  1. Electrons are shared between neighbouring ions
  2. Ions are free to move throughout the lattice
  3. Positive and negative ions are fixed in a regular repeating pattern Correct answer.
  4. Molecules are held by weak intermolecular forces

Explanation

In an ionic solid the ions are held in fixed positions by strong electrostatic attractions, arranged in a regular repeating lattice. The ions cannot move, which is why solid ionic compounds do not conduct electricity.

Question 35Chemistry achievement standards (Level 2) - content domains not enumerated in source

A student mixes 50.0 mL of 0.200 mol L−1 sodium chloride solution with 50.0 mL of 0.200 mol L−1 silver nitrate solution. The precipitate is AgCl. What amount of AgCl precipitate could form?

  1. 0.0100 mol Correct answer.
  2. 0.200 mol
  3. 0.00500 mol
  4. 0.0200 mol

Explanation

Each reactant has n = 0.0500 × 0.200 = 0.0100 mol, and the reaction uses them in a 1:1 ratio. Therefore 0.0100 mol of AgCl can form.

Question 36Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which functional group is present in propan-2-ol, CH3CH(OH)CH3?

  1. Carboxyl group
  2. Ester group
  3. Hydroxyl group Correct answer.
  4. Carbonyl group

Explanation

Propan-2-ol contains an –OH group attached to a saturated carbon, which is a hydroxyl group and makes the compound an alcohol. The other groups contain a C=O or a –COOH unit, which are absent here.

Question 37Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which equation shows the correct half-reaction for the reduction of permanganate to Mn2+ in acidic solution?

  1. MnO4− + 8H+ + 5e− → Mn2+ + 4H2O Correct answer.
  2. MnO4− → Mn2+ + 4H2O + 5e−
  3. MnO4− + e− → MnO42−
  4. MnO4− + 4H+ + 3e− → MnO2 + 2H2O

Explanation

Reduction involves gaining electrons, so the electrons must appear on the reactant side. The balanced half-reaction also conserves mass and charge: 8H+ and 5e− on the left balance Mn2+ and 4H2O on the right.

Question 38Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which statement explains why the boiling point of ethanol (Mr = 46) is higher than that of propane (Mr = 44), despite their similar molar masses?

  1. Ethanol has a larger molar mass, which always raises the boiling point
  2. Ethanol molecules are held by hydrogen bonds, whereas propane molecules are held only by dispersion forces Correct answer.
  3. Propane molecules are polar, whereas ethanol molecules are non-polar
  4. Propane forms hydrogen bonds between its carbon atoms

Explanation

The –OH group in ethanol allows hydrogen bonding between molecules, which is much stronger than the dispersion forces between non-polar propane molecules. More energy is therefore needed to separate ethanol molecules.

Question 39Chemistry achievement standards (Level 2) - content domains not enumerated in source

In an electrochemical cell, which change occurs at the anode?

  1. No reaction occurs at the anode in a galvanic cell
  2. Reduction, with electrons gained by the electrode
  3. Oxidation, with electrons released by the electrode Correct answer.
  4. The anode always has a positive charge in a galvanic cell

Explanation

Oxidation always occurs at the anode, releasing electrons that travel through the external circuit. In a galvanic cell the anode is the negative electrode, where the metal is oxidised.

Question 40Chemistry achievement standards (Level 2) - content domains not enumerated in source

A reaction has an equilibrium constant Kc of 1 × 10−4 at a given temperature. Which statement best describes the equilibrium mixture?

  1. The reaction rate is very slow compared with other reactions
  2. The equilibrium lies towards the reactants, with only a small amount of product present Correct answer.
  3. The reaction has not yet reached equilibrium
  4. The equilibrium lies towards the products, which are strongly favoured

Explanation

A small Kc means the ratio of products to reactants at equilibrium is much less than one, so the mixture is mostly reactants. The value of Kc gives the position of equilibrium, not the rate.

Question 41Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which pair of solutions would react to produce a gas when mixed?

  1. Sodium chloride solution and potassium nitrate solution
  2. Sodium carbonate solution and hydrochloric acid Correct answer.
  3. Copper(II) sulfate solution and sodium hydroxide solution
  4. Barium chloride solution and sodium sulfate solution

Explanation

Carbonate ions react with acid to form carbon dioxide gas, water and a salt, so mixing sodium carbonate with hydrochloric acid releases CO2. The other pairs produce no gas.

Question 42Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which statement correctly describes the effect of a catalyst on a reaction?

  1. It increases the enthalpy change of the reaction
  2. It changes the position of equilibrium to favour the products
  3. It increases the activation energy so that fewer collisions are effective
  4. It lowers the activation energy by providing an alternative reaction pathway Correct answer.

Explanation

A catalyst provides an alternative pathway with a lower activation energy, so a greater fraction of collisions are successful. It does not alter the enthalpy change or the equilibrium position.

Question 43Chemistry achievement standards (Level 2) - content domains not enumerated in source

What is the oxidation state of sulfur in the sulfate ion, SO42−?

  1. −2
  2. +4
  3. +6 Correct answer.
  4. +2

Explanation

Each oxygen is assigned −2, giving a total of −8 from the four oxygen atoms. For the overall charge to be −2, sulfur must be +6: (+6) + (−8) = −2.

Question 44Chemistry achievement standards (Level 2) - content domains not enumerated in source

A 0.500 g sample of an organic compound is burned completely to give 1.10 g of CO2. What is the mass of carbon in the sample?

  1. 0.300 g Correct answer.
  2. 0.600 g
  3. 0.500 g
  4. 1.10 g

Explanation

Carbon dioxide contains 12.0/44.0 of its mass as carbon, so the carbon mass is 1.10 × 12.0/44.0 = 0.300 g. This is less than the sample mass, as expected.

Question 45Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which statement explains why the atomic radius of sodium is larger than that of chlorine?

  1. Sodium has a full outer shell, which expands the atom
  2. Chlorine has more electron shells than sodium
  3. Sodium has a lower nuclear charge and fewer protons attracting the same number of shells Correct answer.
  4. Chlorine has a larger number of neutrons in its nucleus

Explanation

Sodium and chlorine are in the same period, so their outer electrons are in the same shell. Chlorine has more protons, so its greater nuclear charge pulls the outer electrons closer, giving a smaller radius.

Question 46Chemistry achievement standards (Level 2) - content domains not enumerated in source

Which isomer of C4H10 has a lower boiling point than the straight-chain isomer?

  1. 2-methylpropane Correct answer.
  2. Butane
  3. Neither isomer boils because both are gases
  4. Both isomers have identical boiling points

Explanation

2-methylpropane is more branched, making its molecules more compact and reducing the surface area available for dispersion forces. Weaker dispersion forces lead to a lower boiling point than butane.

Question 47Chemistry achievement standards (Level 2) - content domains not enumerated in source

A buffer solution contains ethanoic acid and sodium ethanoate. Which statement explains how it resists a decrease in pH when a small amount of acid is added?

  1. The sodium ions neutralise the added acid
  2. The ethanoate ions react with the added H+ to form more ethanoic acid Correct answer.
  3. The buffer removes all H+ ions so that the pH cannot change
  4. The ethanoic acid molecules react with the added H+ to form ethanoate ions

Explanation

Added acid increases the H+ concentration, and ethanoate ions from the salt combine with these protons to form weakly ionised ethanoic acid. This removes most of the added H+ and keeps the pH nearly constant.

Question 48Chemistry achievement standards (Level 2) - content domains not enumerated in source

A galvanic cell is set up using Zn2+/Zn (E° = −0.76 V) and Cu2+/Cu (E° = +0.34 V) half-cells. What is the standard cell potential?

  1. +1.10 V Correct answer.
  2. −1.10 V
  3. −0.42 V
  4. +0.42 V

Explanation

The cell potential is the reduction potential of the cathode minus that of the anode: E°cell = 0.34 − (−0.76) = +1.10 V. The positive value shows the reaction is spontaneous as written.

Question 49Chemistry achievement standards (Level 2) - content domains not enumerated in source

For the equilibrium PCl5(g) ⇌ PCl3(g) + Cl2(g), the forward reaction is endothermic. A mixture at equilibrium is heated and the volume is kept constant. Which change is observed?

  1. The mixture becomes darker as more PCl5 forms
  2. The equilibrium constant remains unchanged because only temperature affects pressure
  3. The amount of Cl2 increases because the equilibrium shifts to absorb heat Correct answer.
  4. The amount of Cl2 decreases because the forward reaction is slowed

Explanation

Le Chatelier's principle states that heating an endothermic equilibrium shifts it in the endothermic direction, which here is forward. More PCl3 and Cl2 therefore form as heat is absorbed.

Question 50Chemistry achievement standards (Level 2) - content domains not enumerated in source

A 25.0 mL sample of ethanoic acid solution is titrated with 0.100 mol L−1 NaOH and reaches the equivalence point at 20.0 mL. What is the concentration of the ethanoic acid?

  1. 0.0500 mol L−1
  2. 0.100 mol L−1
  3. 0.0800 mol L−1 Correct answer.
  4. 0.125 mol L−1

Explanation

The acid and base react in a 1:1 ratio, so n(acid) = n(base) = 0.0200 × 0.100 = 0.00200 mol. Dividing by the acid volume of 0.0250 L gives 0.0800 mol L−1.