IGCSE Chemistry Practice Test 3

Correct: (A)

Sublimation is the change from a solid directly to a gas, without passing through the liquid state.

Correct: (B)

At constant temperature the particles move at the same average speed, but compression pushes them closer together, so pressure increases.

Correct: (C)

Ammonia (Mr = 17) is lighter than hydrogen chloride (Mr = 36.5), so ammonia particles diffuse faster and travel further before the two gases meet.

Correct: (D)

Number of neutrons = nucleon number – proton number = 23 – 11 = 12.

Correct: (B)

The shells fill as 2 in the first shell, 8 in the second, leaving 12 – 10 = 2 electrons in the third shell.

Correct: (C)

Isotopes have the same number of protons (and electrons, so the same chemistry) but different numbers of neutrons.

Correct: (D)

In diamond every carbon atom is covalently bonded to four others in a giant lattice. Sodium chloride is giant ionic, and iodine and water are simple molecular.

Correct: (A)

Ionic compounds are held together by strong electrostatic attraction between positive and negative ions in a giant lattice.

Correct: (C)

The oxide ion is formed when an oxygen atom gains 2 electrons: 8 + 2 = 10 electrons.

Correct: (D)

An oxygen molecule has a double bond (O=O). H2, HCl and Cl2 each contain only a single covalent bond.

Correct: (A)

In a metal, the outer electrons are delocalised and can move through the lattice carrying the charge. The ions stay in fixed positions in the solid.

Correct: (B)

Mr = 40 + 12 + (3 × 16) = 40 + 12 + 48 = 100.

Correct: (D)

Moles = mass / Mr = 8 / 16 = 0.50 mol.

Correct: (A)

The ratio H2 : O2 is 2 : 1, so the oxygen volume = 48 / 2 = 24 dm^3.

Correct: (B)

C: 80/12 = 6.67; H: 20/1 = 20. Ratio = 6.67 : 20 = 1 : 3, so the empirical formula is CH3.

Correct: (C)

Moles = 5.85 / 58.5 = 0.10 mol. Concentration = 0.10 / 0.500 = 0.20 mol/dm^3.

Correct: (A)

Percentage yield = (actual yield / theoretical yield) × 100 = (32 / 40) × 100 = 80%.

Correct: (C)

Moles of CaCO3 = 10 / 100 = 0.10 mol, which forms 0.10 mol of CO2. Mass = 0.10 × 44 = 4.4 g.

Correct: (B)

At the cathode, hydrogen ions are discharged in preference to sodium ions because sodium is high in the reactivity series, so hydrogen gas is formed.

Correct: (D)

The positive lead(II) ions move to the negative electrode, gain electrons and form molten lead.

Correct: (B)

Copper is below hydrogen in the reactivity series, so copper(II) ions are discharged in preference to hydrogen ions, and copper metal coats the cathode.

Correct: (D)

The object to be plated is always the cathode, and the electrolyte must contain ions of the plating metal, here Ag^+ from silver nitrate.

Correct: (A)

Zinc is more reactive than copper, so zinc is the negative electrode; it loses electrons, which flow through the external wire to the copper electrode.

Correct: (C)

Combustion releases heat energy to the surroundings, so it is exothermic. The other three processes take in energy.

Correct: (D)

Energy absorbed breaking bonds = 436 + 242 = 678 kJ. Energy released forming bonds = 2 × 431 = 862 kJ. Overall change = 678 – 862 = -184 kJ/mol.

Correct: (C)

Energy = mass × specific heat capacity × temperature change = 50 × 4.2 × 10 = 2100 J = 2.1 kJ.

Correct: (A)

An endothermic reaction takes in heat from the surroundings, so the temperature of the surroundings falls.

Correct: (B)

Hydrogen burns in oxygen to form only water: 2H2 + O2 → 2H2O. The other fuels also produce carbon dioxide.

Correct: (C)

Raising the temperature gives the particles more energy, so collisions are more frequent and more energetic, increasing the rate.

Correct: (A)

A higher concentration means more particles per unit volume, so successful collisions occur more often.

Correct: (D)

A catalyst speeds up the reaction by lowering the activation energy; it is not used up and does not change the yield.

Correct: (B)

For an exothermic forward reaction, raising the temperature shifts the equilibrium in the endothermic (backward) direction, so the yield of ammonia decreases.

Correct: (B)

Zinc atoms lose electrons to form Zn^2+ ions. Loss of electrons is oxidation, so zinc is oxidised (copper(II) ions are reduced).

Correct: (D)

In (D) magnesium is oxidised (0 to +2) and hydrogen is reduced (+1 to 0). The others involve no change in oxidation state.

Correct: (C)

At equilibrium the forward and reverse reactions continue at equal rates, so the concentrations stay constant (they do not have to be equal).

Correct: (A)

Strong alkalis have a high pH, typically 13-14 on the pH scale.

Correct: (B)

Sulfur dioxide is a non-metal oxide and is acidic; it reacts with alkalis and forms sulfurous/sulfuric acid in water. The others are basic metal oxides.

Correct: (D)

Copper(II) sulfate is made from an insoluble base/carbonate and acid; filtration removes the excess solid, and crystallisation gives pure crystals. Copper metal does not react with dilute sulfuric acid.

Correct: (C)

Barium sulfate is insoluble, so it is made by mixing solutions of a soluble barium salt and a soluble sulfate, then filtering, washing and drying the precipitate.

Correct: (A)

Ba^2+ ions form a white precipitate of barium sulfate with sulfate ions; the acid is added first to remove carbonate ions, which would also give a white precipitate.

Correct: (C)

Acid + carbonate → salt + water + carbon dioxide, e.g. 2HCl + CaCO3 → CaCl2 + H2O + CO2.

Correct: (A)

Orange corresponds to about pH 4-5, which is a weak acid. A strong acid would turn the indicator red, and alkalis give blue/purple.

Correct: (B)

Three shells of electrons means Period 3, and 6 electrons in the outer shell means Group VI (it is sulfur).

Correct: (D)

Reactivity increases down Group I (lithium reacts gently with water, potassium reacts violently), because the outer electron is further from the nucleus and is lost more easily.

Correct: (D)

Transition elements form coloured compounds (e.g. blue copper(II) sulfate), have high melting points and variable oxidation states.

Correct: (B)

The colours get darker down Group VII, while reactivity decreases.

Correct: (C)

Magnesium is the highest of these metals in the reactivity series, so it reacts most vigorously, producing hydrogen rapidly.

Correct: (A)

Carbon monoxide, formed from coke, reduces the iron(III) oxide: Fe2O3 + 3CO → 2Fe + 3CO2.

Correct: (A)

Aluminium is light (low density) and its protective oxide layer makes it corrosion-resistant, which is ideal for aircraft.

Correct: (D)

Rusting needs both oxygen and water; a paint layer forms a barrier that excludes both from the iron surface.

Correct: (B)

Carbon dioxide from burning fossil fuels contributes to the enhanced greenhouse effect and global warming.

Correct: (C)

Fertilisers supply nitrogen, phosphorus and potassium (NPK). Ammonium nitrate supplies nitrogen, which plants need for growth.

Correct: (B)

Filtration (through sand beds) removes insoluble solid particles; chlorine is added separately to kill microorganisms.

Correct: (A)

Ethane is an alkane with two carbon atoms: CnH2n+2 gives C2H6.

Correct: (C)

Alkenes have the general formula CnH2n, so C3H6 is an alkene (propene). The others are alkanes.

Correct: (D)

Alkenes have a C=C double bond and decolourise bromine water by addition. Alkanes do not react with bromine water in the dark.

Correct: (C)

Fermentation uses enzymes in yeast, works best at about 30 °C, and air must be kept out so the ethanol is not oxidised.

Correct: (D)

The monomer has the same name as the polymer without "poly": propene molecules join together to form poly(propene).

Correct: (A)

Ag^+ ions form a white precipitate of silver chloride with chloride ions.

Correct: (B)

Rf = distance moved by dye / distance moved by solvent, so distance moved by dye = 0.80 × 10.0 = 8.0 cm.