IGCSE Chemistry Practice Test 9

Correct: (A)

When a gas cools and becomes a liquid, the change is called condensation.

Correct: (B)

In a solid the particles are held in fixed positions by strong forces and can only vibrate about those positions.

Correct: (C)

The bromine particles mix with the air particles by diffusion, which happens because particles are in continuous random motion.

Correct: (D)

Mass number = protons + neutrons = 11 + 12 = 23.

Correct: (A)

Magnesium has 12 electrons, arranged in shells as 2, 8, 2.

Correct: (D)

Isotopes have the same proton number but different numbers of neutrons, so their mass numbers differ.

Correct: (C)

Magnesium oxide is ionic: magnesium atoms transfer electrons to oxygen atoms. Carbon dioxide, methane and water are covalent.

Correct: (D)

Carbon has four outer electrons and forms four single covalent bonds, one to each hydrogen atom.

Correct: (A)

Diamond is a giant covalent structure in which every carbon atom forms four strong covalent bonds, so a huge amount of energy is needed to break them.

Correct: (C)

In a metal the outer electrons are delocalised and can move through the structure, carrying the electric charge.

Correct: (C)

Oxide ions are O^2-. For the compound to be neutral: 2(x) + 3(-2) = 0, so x = +3.

Correct: (B)

Moles = mass / Mr = 8 / 16 = 0.5 mol.

Correct: (A)

Volume = moles × 24 dm^3 = 0.25 × 24 = 6 dm^3.

Correct: (B)

Moles = 2.0 / 40 = 0.05 mol. Concentration = 0.05 mol / 0.500 dm^3 = 0.10 mol/dm^3.

Correct: (D)

10 g CaCO3 = 0.10 mol. This forms 0.10 mol CaO = 0.10 × 56 = 5.6 g.

Correct: (D)

Moles: C = 75/12 = 6.25, H = 25/1 = 25. Ratio C:H = 6.25:25 = 1:4, so the empirical formula is CH4.

Correct: (C)

Percentage yield = (actual / theoretical) × 100 = (30 / 40) × 100 = 75%.

Correct: (B)

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

Correct: (A)

Lead ions, Pb^2+, are positive and move to the negative cathode, where they gain electrons and form lead metal.

Correct: (D)

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

Correct: (C)

In electrolysis the cathode is the negative electrode and attracts positive ions (cations); the anode is positive and attracts negative ions.

Correct: (C)

Water decomposes as 2H2O → 2H2 + O2, so twice the volume of hydrogen is produced compared with oxygen.

Correct: (D)

Graphite conducts electricity and is unreactive (inert), so it does not react with the products of electrolysis.

Correct: (A)

Exothermic reactions release energy to the surroundings, so the temperature of the surroundings rises.

Correct: (B)

Energy to break bonds = 436 + 242 = 678 kJ. Energy released forming bonds = 2 × 431 = 862 kJ. ΔH = 678 – 862 = -184 kJ/mol.

Correct: (C)

Thermal decomposition requires continuous heating and takes in energy from the surroundings, so it is endothermic. The others are exothermic.

Correct: (D)

Particles must collide with at least the activation energy for bonds to break and a reaction to occur.

Correct: (A)

In the fuel cell hydrogen reacts with oxygen to form water only, and the energy change is converted into electricity.

Correct: (C)

A more concentrated acid has more particles in the same volume, so collisions with the marble are more frequent and the rate increases.

Correct: (B)

At a higher temperature particles move faster, collide more frequently, and more of the collisions are successful because they exceed the activation energy.

Correct: (C)

A catalyst provides a different reaction pathway that has a lower activation energy, so more collisions are successful. The catalyst is not used up.

Correct: (B)

The right-hand side has 2 moles of gas compared with 4 moles on the left, so increasing the pressure shifts the equilibrium to the right.

Correct: (D)

Zinc atoms lose electrons to form Zn^2+ ions. Loss of electrons is oxidation, so zinc is oxidised; Cu^2+ ions gain electrons and are reduced.

Correct: (A)

Oxidation is the loss of electrons (OILRIG). A metal atom losing electrons to form a positive ion is oxidation.

Correct: (A)

As the gas escapes, the mass of the reaction mixture decreases, so recording the mass at intervals can be used to follow the rate.

Correct: (A)

Strong acids have very low pH values, around pH 1 when concentrated. pH 7 is neutral and pH 13 is a strong alkali.

Correct: (C)

Acid + carbonate → salt + water + carbon dioxide. The carbon dioxide effervesces during the reaction.

Correct: (B)

For an insoluble base, add it in excess to the warm acid, filter off the leftover solid, then crystallise the zinc sulfate from the filtrate.

Correct: (D)

Sulfate ions react with barium ions to form white barium sulfate, which is insoluble even in dilute hydrochloric acid.

Correct: (C)

Aluminium oxide reacts with both acids and alkalis, so it is amphoteric. Magnesium oxide is basic; carbon dioxide and sulfur dioxide are acidic.

Correct: (C)

Methyl orange is yellow in alkali and turns orange/red in acid, so at the end-point it changes from yellow to orange/red.

Correct: (B)

Calcium oxide is a basic oxide: it reacts with acids but not with alkalis. Zinc oxide and aluminium oxide are amphoteric; silicon dioxide is acidic and unreactive with most acids.

Correct: (B)

Group I metals become more reactive down the group (lithium < sodium < potassium) because the outer electron is further from the nucleus and is lost more easily.

Correct: (D)

Chlorine is more reactive than bromine, so it displaces bromine from potassium bromide: Cl2 + 2KBr → 2KCl + Br2. The bromine colours the solution orange.

Correct: (C)

Transition elements form coloured compounds, often have variable oxidation states, and many act as catalysts, e.g. iron in the Haber process.

Correct: (A)

Noble gas atoms already have a full outer electron shell, so they do not need to gain, lose or share electrons.

Correct: (D)

Sodium is a very reactive Group I metal and reacts vigorously with cold water, forming sodium hydroxide (alkaline) and hydrogen. Copper does not react, and iron and zinc react only with steam.

Correct: (B)

Carbon monoxide reduces iron(III) oxide: Fe2O3 + 3CO → 2Fe + 3CO2. Limestone removes impurities as slag.

Correct: (A)

Brass is an alloy of copper and zinc. Copper and tin make bronze; iron and carbon make steel.

Correct: (D)

Galvanising coats iron with zinc, which acts as a barrier; if the coating is scratched, the more reactive zinc corrodes instead of the iron (sacrificial protection).

Correct: (B)

Chlorine is added to drinking water as a sterilising agent to kill harmful microorganisms.

Correct: (A)

NPK fertilisers contain the three essential elements nitrogen (N), phosphorus (P) and potassium (K).

Correct: (D)

When the algae die, bacteria decompose them and use up dissolved oxygen during respiration, so the fish suffocate (eutrophication).

Correct: (B)

Alkanes are saturated hydrocarbons with the general formula CnH2n+2.

Correct: (B)

Ethene is unsaturated and undergoes an addition reaction with bromine across the C=C bond, so the orange colour disappears.

Correct: (A)

Fermentation uses yeast enzymes at about 30°C under anaerobic conditions (no air), producing ethanol and carbon dioxide.

Correct: (C)

Carboxylic acids contain the -COOH functional group; -OH is in alcohols and C=C is in alkenes.

Correct: (D)

In addition polymerisation, the C=C bonds of many ethene monomers open up and join together to form the polymer, with no by-product.

Correct: (B)

Chloride ions form a white precipitate of silver chloride with silver nitrate solution (after acidifying with dilute nitric acid).

Correct: (A)

Rf = distance moved by the substance / distance moved by the solvent front = 4.0 / 10.0 = 0.4.