IGCSE Chemistry Practice Test 18

Correct: (C)

In a gas such as steam the particles are far apart and move freely, unlike in solids and liquids.

Correct: (A)

Evaporation occurs at the surface, at any temperature, when faster-moving particles escape the liquid.

Correct: (D)

Diffusion happens because particles move randomly and spread from higher to lower concentration.

Correct: (B)

Every atom of the same element has the same number of protons; a different proton number means a different element.

Correct: (D)

Sodium has 11 electrons: 2 in the first shell, 8 in the second and 1 in the third shell.

Correct: (B)

The atom gains one electron to form Cl^-, so the ion has 17 + 1 = 18 electrons.

Correct: (A)

The giant ionic lattice is held together by strong attractions in all directions, requiring a lot of thermal energy to break down.

Correct: (C)

Each carbon atom in graphite forms three bonds, leaving one electron per atom delocalised and able to carry charge.

Correct: (A)

Boiling separates the molecules; the weak forces between molecules need little energy, although the covalent bonds inside stay intact.

Correct: (D)

Methane consists of molecules held together by shared pairs of electrons; the others are ionic compounds.

Correct: (C)

Ar takes account of the masses and relative abundances of all the isotopes of the element.

Correct: (B)

500 cm^3 = 0.500 dm^3, so concentration = 0.10 / 0.500 = 0.20 mol/dm^3.

Correct: (B)

Mass = moles × Mr = 0.50 × 100 = 50 g.

Correct: (C)

Volume = 2.0 × 24 = 48 dm^3.

Correct: (A)

Moles: C = 27.3/12 = 2.28, O = 72.7/16 = 4.54; ratio 1 : 2 gives CO2.

Correct: (D)

Percentage purity = (9.0 / 10) × 100 = 90%.

Correct: (D)

Hydrogen is the limiting reactant: 2.0 mol of H2 needs only 1.0 mol of O2 and forms 2.0 mol of H2O.

Correct: (A)

Concentration = mass / volume = 8.0 / 2.0 = 4.0 g/dm^3.

Correct: (B)

In concentrated solution, chloride ions are discharged at the positive anode to form chlorine gas.

Correct: (C)

Hydrogen ions gain electrons at the cathode to form hydrogen gas.

Correct: (A)

Cations are positive ions, so they are attracted to the negative cathode.

Correct: (C)

Cryolite lowers the working temperature of the electrolyte from over 2000°C to about 950°C.

Correct: (D)

A voltaic cell uses a spontaneous chemical reaction to produce an electric current.

Correct: (B)

An endothermic reaction takes in thermal energy from the surroundings, so their temperature falls.

Correct: (C)

If bond formation releases more energy than bond breaking absorbs, the excess is given out as heat.

Correct: (D)

Bonds broken = 436 + (498/2) = 685; bonds made = 2 × 464 = 928; ΔH = 685 – 928 = -243 kJ/mol.

Correct: (B)

Only collisions with energy at least equal to the activation energy can result in a reaction.

Correct: (A)

Hydrogen burns to form only water, so it does not add carbon dioxide to the atmosphere.

Correct: (B)

At higher pressure the same number of particles occupies a smaller volume, increasing the collision frequency.

Correct: (A)

A gas syringe collects and measures the gas volume at timed intervals so the rate can be calculated.

Correct: (C)

At equilibrium both reactions still occur, but at the same rate, so concentrations stay constant.

Correct: (D)

About 450°C gives an acceptable yield of ammonia at a reasonable rate; lower temperatures would be too slow.

Correct: (D)

Cu^2+ gains the electrons lost by zinc, so Cu^2+ causes oxidation and is the oxidising agent.

Correct: (C)

A reducing agent reduces the purple manganate(VII) ions to almost colourless Mn^2+ ions.

Correct: (A)

Iron gains oxygen as it rusts, forming hydrated iron(III) oxide, so it is oxidised.

Correct: (B)

A base accepts a hydrogen ion (proton) from an acid during a reaction.

Correct: (A)

Universal indicator is red at very low pH, green at pH 7 and purple in strong alkali.

Correct: (B)

The solution is evaporated to the crystallisation point, cooled, and the crystals are filtered, washed and dried.

Correct: (D)

Excess insoluble oxide ensures all the acid reacts; the unreacted solid is filtered off before crystallisation.

Correct: (C)

Non-metal oxides such as sulfur dioxide are acidic; metal oxides are usually basic.

Correct: (C)

Carbonates react with dilute acid to give carbon dioxide, which turns limewater milky.

Correct: (A)

Hydrochloric acid gives chlorides, nitric acid gives nitrates and sulfuric acid gives sulfates.

Correct: (B)

The halogens become less reactive down the group; fluorine is the most reactive and iodine the least of the common halogens.

Correct: (D)

Period 3 contains Na, Mg, Al and the non-metals; the Group II member is magnesium.

Correct: (B)

Transition elements form ions with different charges, for example Fe^2+ and Fe^3+, and their compounds are often coloured.

Correct: (D)

Reactivity increases down Group I, so potassium reacts more vigorously with water than lithium or sodium.

Correct: (C)

Metals below carbon in the reactivity series are extracted by carbon reduction; more reactive metals need electrolysis.

Correct: (A)

Aluminium is more reactive than iron, so it removes oxygen from iron(III) oxide, producing molten iron.

Correct: (D)

Aluminium is light for its strength and its oxide layer protects it from further corrosion.

Correct: (B)

Zinc is more reactive than iron, so it acts as a barrier and also protects sacrificially if the coating is scratched.

Correct: (A)

The alkali reacts with the ammonium salt: NH4^+ + OH^- → NH3 + H2O, so the nitrogen escapes as ammonia gas instead of feeding the plants.

Correct: (C)

Methane and carbon dioxide absorb infrared radiation and contribute to the enhanced greenhouse effect.

Correct: (A)

Ammonium nitrate, NH4NO3, is a widely used nitrogenous fertiliser.

Correct: (D)

Alkenes contain one C=C double bond and have the general formula CnH2n.

Correct: (B)

The C=C bond in an alkene reacts with bromine in an addition reaction, removing the orange colour.

Correct: (C)

Alcohols contain the hydroxyl functional group, -OH, attached to a carbon chain.

Correct: (C)

In condensation polymerisation, monomers join by reacting together and eliminating a small molecule, usually water.

Correct: (B)

Cracking breaks long-chain hydrocarbons into shorter, more useful alkanes and alkenes.

Correct: (D)

Oxygen relights a glowing splint; this is the standard test for the gas.

Correct: (A)

Pure substances melt sharply at one temperature, while impure samples melt over a range at a lower temperature.