IGCSE Chemistry Practice Test 14

Correct: (C)

Condensation is the change from a gas to a liquid, which happens when the vapour loses energy on the cold surface.

Correct: (D)

Only the fastest-moving particles have enough energy to escape; their loss lowers the average kinetic energy, and therefore the temperature, of the liquid left behind.

Correct: (A)

Heating gives the particles more kinetic energy, so they collide with the container walls more frequently and more forcefully, increasing the pressure.

Correct: (B)

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

Correct: (B)

2 + 8 + 1 = 11 electrons, so the proton number is 11, which is sodium.

Correct: (A)

The atom loses its two outer electrons when forming Mg^2+, leaving 2,8, the stable configuration of neon.

Correct: (D)

In covalent bonding, non-metal atoms share pairs of electrons so that each atom achieves a stable outer shell.

Correct: (C)

Diamond has a giant covalent (macromolecular) structure in which every carbon atom forms four strong covalent bonds, making it extremely hard.

Correct: (D)

Sodium chloride consists of a regular lattice of Na^+ and Cl^- ions held together by strong electrostatic forces; water and carbon dioxide are simple molecular, and diamond is giant covalent.

Correct: (C)

Silicon dioxide is a giant covalent structure; melting it requires breaking many strong Si-O covalent bonds, which takes a lot of energy.

Correct: (B)

Metallic bonding is the attraction between the lattice of positive ions and the delocalised electrons that move throughout the structure.

Correct: (A)

Moles = mass / Mr = 44 / 44 = 1.0 mol.

Correct: (A)

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

Correct: (B)

Moles of C = 2.4 / 12 = 0.20; moles of H = 0.40 / 1 = 0.40. The ratio C : H = 0.20 : 0.40 = 1 : 2, so the empirical formula is CH2.

Correct: (C)

Moles of MgO = 4.0 / 40 = 0.10 mol, so 0.10 mol of Mg is needed. Mass = 0.10 × 24 = 2.4 g.

Correct: (D)

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

Correct: (C)

Moles of HCl = 0.0200 dm^3 × 0.10 = 0.0020 mol, so 0.0020 mol of NaOH reacted. Concentration = 0.0020 / 0.0250 = 0.080 mol/dm^3.

Correct: (A)

Percentage yield = (6.0 / 8.0) × 100 = 75%.

Correct: (B)

Hydrogen ions are discharged at the cathode to give hydrogen gas; oxygen is formed at the anode.

Correct: (D)

The bromide ions lose electrons at the anode to form bromine; lead is deposited at the cathode.

Correct: (D)

Ions must be free to move and carry charge to the electrodes; in the solid lattice they are locked in place.

Correct: (B)

The object to be plated is made the cathode, so that positive silver ions are attracted to it and form a layer of silver metal on its surface.

Correct: (A)

The hydroxide ions from water are discharged at the anode to give oxygen; copper is deposited at the cathode.

Correct: (C)

A fall in temperature shows the reaction has taken energy in from the surroundings, so it is endothermic.

Correct: (A)

Energy to break bonds = 436 + 193 = 629 kJ. Energy released forming bonds = 2 × 366 = 732 kJ. ΔH = 629 – 732 = -103 kJ/mol.

Correct: (D)

The products have more energy than the reactants, so energy has been taken in: the reaction is endothermic and ΔH is positive.

Correct: (C)

Fossil fuels such as coal, oil and gas are used up far faster than they form, so they are non-renewable.

Correct: (B)

A chemical cell (such as two different metals in an electrolyte) converts chemical energy into electrical energy.

Correct: (B)

A more concentrated acid has more acid particles in the same volume, so collisions with the marble are more frequent and the reaction is faster.

Correct: (C)

At higher temperatures particles move faster, colliding more frequently, and a greater proportion of collisions are energetic enough to react.

Correct: (D)

Lowering the temperature shifts the equilibrium in the exothermic direction (to the right), so more SO3 is formed, although the reaction is slower.

Correct: (A)

Oxidation is the loss of electrons (OIL: Oxidation Is Loss); reduction is the gain of electrons.

Correct: (D)

Hydrogen gains oxygen to form water, so hydrogen is oxidised; copper(II) oxide loses oxygen, so it is reduced.

Correct: (A)

2 minutes = 120 s. Rate = 120 cm^3 / 120 s = 1.0 cm^3/s.

Correct: (B)

A catalyst lowers the activation energy of both the forward and reverse reactions by the same amount, so equilibrium is reached faster but its position and the yield are unchanged.

Correct: (C)

The alkali neutralises the acid, using up hydrogen ions, so the pH rises from a low value towards 7.

Correct: (A)

Magnesium oxide is a metal oxide and reacts with acids to form a salt and water, so it is basic; the others are non-metal oxides and are acidic.

Correct: (C)

Mixing solutions containing Pb^2+ and SO4^2- ions gives an immediate white precipitate of insoluble lead(II) sulfate.

Correct: (D)

Ammonium compounds release ammonia gas when warmed with an alkali; ammonia is alkaline and turns damp red litmus paper blue.

Correct: (B)

Acid + carbonate → salt + water + carbon dioxide; effervescence is seen as the gas is released.

Correct: (C)

Evaporating to the crystallisation point and cooling produces crystals; filtering and drying them between filter papers gives a pure sample. Boiling to dryness would drive the water of crystallisation from the hydrated salt.

Correct: (B)

Universal indicator is green at pH 7; it is red in strong acids and blue/purple in alkalis.

Correct: (A)

Halogens become less reactive down the group because the outer shell is further from the nucleus, so the atom attracts an extra electron less strongly.

Correct: (D)

Down Group 7 the halogens become darker, change from gases to solids (F2 and Cl2 gases, Br2 liquid, I2 solid), and become less reactive, so astatine is predicted to be a dark solid and the least reactive.

Correct: (B)

Finely divided iron is the catalyst used in the Haber process.

Correct: (D)

Chemical behaviour depends on the outer-shell electrons, and elements in a group all have the same number of these.

Correct: (C)

In the blast furnace, coke burns to form carbon dioxide and then carbon monoxide, which reduces iron(III) oxide to iron.

Correct: (A)

X is more reactive than zinc (it displaces it) but less reactive than magnesium (it cannot displace it), so X lies between them in the series.

Correct: (A)

Rusting requires both oxygen and water; iron kept in dry air or in oxygen-free water does not rust.

Correct: (B)

Stainless steel contains chromium (and often nickel), which forms a protective oxide layer that prevents rusting.

Correct: (D)

Water passes through filter beds that trap suspended insoluble solids; chlorine is added afterwards to sterilise the water.

Correct: (C)

Air is about 78% nitrogen, 21% oxygen, about 1% argon and 0.04% carbon dioxide.

Correct: (D)

Methane absorbs infrared radiation and contributes to the greenhouse effect, along with carbon dioxide and water vapour; nitrogen, oxygen and argon do not.

Correct: (C)

Alkenes have the general formula CnH2n. For n = 3 this gives C3H6 (propene). The others are alkanes.

Correct: (A)

The hydrogen adds across the C=C double bond, so this is an addition reaction, producing a single product.

Correct: (B)

The industrial hydration of ethene uses steam with a phosphoric acid catalyst at around 300°C and 60-70 atm pressure.

Correct: (B)

The reaction between a carboxylic acid and an alcohol produces an ester (plus water); esters are used in perfumes and flavourings.

Correct: (A)

In condensation polymerisation, two different monomers join with the loss of a small molecule such as water at each linkage.

Correct: (C)

A more soluble substance spends more time dissolved in the moving solvent, so it is carried further up the paper and has a higher Rf value.

Correct: (D)

Chloride ions give a white precipitate of silver chloride with acidified silver nitrate solution. (A cream precipitate would indicate bromide ions and a yellow one iodide ions.)