IGCSE Chemistry Practice Test 8

Correct: (B)

In a solid the particles are packed in a regular arrangement and can only vibrate about fixed positions; in liquids and gases the particles can move around.

Correct: (D)

Evaporation occurs at the surface at any temperature; the particles with the most energy escape, which is why evaporation cools the remaining liquid.

Correct: (A)

Heating gives the particles more kinetic energy, so they hit the container walls harder and more often, increasing the pressure.

Correct: (C)

The number of electrons in a neutral atom equals the proton number: 2 + 8 + 1 = 11 (sodium).

Correct: (D)

Neutrons = nucleon number – proton number = 14 – 6 = 8.

Correct: (B)

In solid sodium chloride the ions are locked in the lattice and cannot move, so it does not conduct. On melting, the ions become free to move and carry charge.

Correct: (C)

Boiling separates the molecules; only the weak intermolecular forces are overcome. The strong covalent bonds inside each molecule stay intact.

Correct: (A)

In a metal the outer electrons are delocalised, forming a 'sea' of electrons that can move and carry charge through the lattice of positive ions.

Correct: (D)

Oxygen (2,6) gains two electrons to form O^2- with configuration 2,8. F is 2,7, Na is 2,8,1 and S^2- is 2,8,8.

Correct: (B)

In diamond every carbon atom is held by four strong covalent bonds in a rigid giant lattice, so a very large amount of energy is needed to break the structure.

Correct: (C)

Carbon dioxide exists as small separate CO2 molecules. SiO2 is giant covalent, NaCl is ionic and Mg is a metal.

Correct: (A)

Moles = mass / Mr = 4.4 / 44 = 0.1 mol.

Correct: (D)

Volume = moles × 24 = 2.0 × 24 = 48 dm^3.

Correct: (B)

Concentration = moles / volume in dm^3 = 2.0 / 0.500 = 4.0 mol/dm^3.

Correct: (C)

Mr of CaCO3 = 40 + 12 + (3 × 16) = 100. Percentage of Ca = (40 / 100) × 100 = 40%.

Correct: (A)

Moles of Mg = 2.4 / 24 = 0.10 mol, so 0.10 mol of H2 forms. Volume = 0.10 × 24 = 2.4 dm^3.

Correct: (D)

Moles of Cu = 3.2 / 64 = 0.05; moles of O = 0.8 / 16 = 0.05. The ratio Cu : O = 1 : 1, so the formula is CuO.

Correct: (B)

Percentage purity = (20.0 / 25.0) × 100 = 80%.

Correct: (C)

Chloride ions move to the positive electrode and lose electrons: 2Cl^- – 2e^- → Cl2. Potassium forms at the negative electrode.

Correct: (A)

Copper is below hydrogen in the reactivity series, so Cu^2+ ions are discharged in preference to H^+ ions and a layer of copper forms on the cathode. Oxygen forms at the anode.

Correct: (D)

Cations are attracted to the cathode (negative electrode) and anions to the anode. The current is carried through the electrolyte by moving ions, not electrons.

Correct: (B)

Cryolite lowers the working temperature of the electrolyte from over 2000°C to about 950°C, saving a large amount of energy.

Correct: (C)

The voltage of a simple cell depends on the difference in reactivity of the two metals: the further apart they are in the reactivity series, the greater the voltage.

Correct: (A)

A fall in temperature means energy has been absorbed from the surroundings, so dissolving ammonium nitrate is endothermic (the basis of some cold packs).

Correct: (D)

Energy absorbed breaking bonds = 945 + (3 × 436) = 2253 kJ. Energy released forming bonds = 6 × 391 = 2346 kJ. ΔH = 2253 – 2346 = -93 kJ/mol.

Correct: (B)

Energy = m × c × ΔT = 200 × 4.2 × 15 = 12 600 J = 12.6 kJ.

Correct: (C)

The activation energy is the minimum energy barrier that particles must overcome in a collision for bonds to break and a reaction to happen.

Correct: (A)

Plants take in energy from sunlight for photosynthesis, so it is endothermic. Respiration, neutralisation and combustion are all exothermic.

Correct: (D)

Larger pieces have a smaller surface area, so acid particles collide with the zinc less frequently and the rate falls.

Correct: (B)

With more particles crowded into the same volume, collisions happen more often, so more reactions occur per second.

Correct: (C)

At dynamic equilibrium both reactions continue at the same rate, so there is no overall change in the amounts of substances.

Correct: (A)

The Haber process uses about 450°C, about 200 atm pressure and an iron catalyst, a compromise between rate and equilibrium yield.

Correct: (D)

Let the oxidation number of S be x. x + 4(-2) = -2, so x = +6.

Correct: (B)

Oxidation is loss of electrons (and reduction is gain of electrons). It can happen with or without oxygen being involved.

Correct: (C)

Raising the temperature favours the endothermic direction, which is the reverse reaction here, so the equilibrium shifts to the left and less ammonia is present.

Correct: (A)

Acids react with carbonates to give a salt, water and carbon dioxide, which causes the effervescence.

Correct: (D)

A pH above 7 shows an alkali; a weak alkali such as aqueous ammonia has a pH of about 9-10, lower than a strong alkali of the same concentration.

Correct: (B)

Calcium oxide is a metal oxide that reacts with acids, so it is basic. The others are non-metal oxides and are acidic.

Correct: (C)

Precipitation is used for insoluble salts: barium sulfate is insoluble, so solutions of a barium salt and a sulfate are mixed and the solid barium sulfate is filtered off. The other salts are soluble.

Correct: (A)

Ag^+ ions form white insoluble silver chloride with Cl^- ions. The nitric acid is added first to remove carbonate ions that would also precipitate.

Correct: (D)

A metal oxide reacts with an acid to give a salt and water; with sulfuric acid the salt is a sulfate: ZnO + H2SO4 → ZnSO4 + H2O.

Correct: (B)

Calcium hydroxide (slaked lime) is an alkali that neutralises the excess acid in the soil. The other substances are neutral or acidic fertiliser salts.

Correct: (C)

The number of electrons in the outer shell (2) gives the group number, so the element (magnesium) is in Group II. It is in Period 3 because it has three shells.

Correct: (A)

Bromine is above iodine in the group and is more reactive, so it displaces iodine from potassium iodide. Iodine cannot displace bromine or chlorine, and bromine cannot displace chlorine.

Correct: (D)

Group I metals are soft, have low densities and low melting points, and become more reactive down the group because their outer electron is lost more easily.

Correct: (B)

Noble gas atoms already have a full outer electron shell (or a complete duplet for helium), so they do not need to gain, lose or share electrons.

Correct: (C)

Copper is below hydrogen in the reactivity series, so it cannot displace hydrogen from dilute acids. Zinc, iron and magnesium all react, magnesium most vigorously.

Correct: (A)

Aluminium is a reactive metal high in the reactivity series, so it is extracted by electrolysis of molten aluminium oxide. Iron is extracted by reduction in a blast furnace; copper and lead by reduction/roasting of their ores.

Correct: (D)

The nail in dry air has oxygen but no water, and the nail in boiled water has water but almost no dissolved air; neither rusts. Rusting requires oxygen and water together.

Correct: (B)

Bronze is copper alloyed with tin. (Brass is copper and zinc; steel is iron and carbon.)

Correct: (C)

Water is filtered to remove solids and then treated with chlorine, which kills bacteria and other microorganisms. Sedimentation just allows solids to settle.

Correct: (A)

When fuels burn in a limited supply of air (e.g. in car engines), carbon monoxide, a poisonous gas, is formed instead of carbon dioxide.

Correct: (D)

Green plants take in carbon dioxide for photosynthesis, removing it from the air. Combustion, respiration and decay all release carbon dioxide back into the atmosphere.

Correct: (B)

With a plentiful supply of oxygen, methane burns completely: CH4 + 2O2 → CO2 + 2H2O.

Correct: (C)

Alkenes are unsaturated (general formula CnH2n) with a carbon-carbon double bond that undergoes addition reactions, e.g. decolourising bromine water.

Correct: (A)

Ethene + steam → ethanol at about 300°C and 60 atm pressure with a concentrated phosphoric acid catalyst. (Hydrogen and nickel convert ethene to ethane; yeast is used in fermentation, not with ethene.)

Correct: (D)

Addition polymers have very unreactive long chains, so they do not break down in the environment and create long-lasting waste.

Correct: (B)

A weak acid is only partly ionised (dissociated) in water, unlike a strong acid such as hydrochloric acid, which is fully ionised. Ethanoic acid still reacts normally with bases, alkalis and carbonates.

Correct: (C)

A pure substance gives a single spot on a chromatogram, while a mixture separates into two or more spots.

Correct: (A)

Oxygen relights a glowing splint. (Limewater detects carbon dioxide, the pop test detects hydrogen, and bleaching of litmus indicates chlorine.)