IGCSE Chemistry Practice Test 2

Correct: (C)

Condensation is the change from a gas to a liquid, which happens when the gas is cooled.

Correct: (A)

Evaporation takes place at the surface of a liquid at any temperature; boiling takes place throughout the liquid at the boiling point.

Correct: (D)

The diffusion of bromine shows that gas particles are in constant random motion and spread out to fill all the space available.

Correct: (B)

Nucleon number = number of protons + number of neutrons = 9 + 10 = 19.

Correct: (B)

Neutrons have no charge; protons have a relative charge of +1 and electrons have a relative charge of -1.

Correct: (D)

The atom has 6 electrons in its outer shell, so the element is in Group VI (it is sulfur).

Correct: (A)

A calcium atom (2,8,8,2) loses its two outer electrons, leaving the Ca^2+ ion with the configuration 2,8,8.

Correct: (C)

Methane consists of small molecules with weak forces between them, so very little energy is needed to separate the molecules and its melting point is low.

Correct: (A)

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

Correct: (B)

A double bond consists of two shared pairs of electrons, which is 4 electrons in total.

Correct: (C)

In graphite the carbon atoms form layers; the forces between the layers are weak, so the layers can slide over each other easily.

Correct: (D)

Mr = 24 + 32 + (4 × 16) = 24 + 32 + 64 = 120.

Correct: (D)

Mass = moles × Mr = 0.25 × 100 = 25 g.

Correct: (C)

Moles = volume / molar volume = 480 cm^3 / 24000 cm^3 = 0.020 mol.

Correct: (B)

Moles = concentration × volume in dm^3 = 0.100 × 0.0250 = 0.00250 mol.

Correct: (A)

The mass of the empirical formula is (2 × 12) + (5 × 1) = 29. 58 / 29 = 2, so the molecular formula is 2 × C2H5 = C4H10.

Correct: (B)

Mr of CO2 = 12 + (2 × 16) = 44. Percentage of oxygen = (32 / 44) × 100 = 72.7%.

Correct: (A)

Moles of Mg = 2.4 / 24 = 0.10 mol. Mg + 2HCl → MgCl2 + H2, so 0.10 mol of H2 is formed; volume = 0.10 × 24 = 2.4 dm^3.

Correct: (C)

In a concentrated solution, chloride ions are discharged at the anode in preference to hydroxide ions, forming chlorine gas.

Correct: (D)

At the cathode, cations (positive ions) gain electrons and are reduced to form atoms.

Correct: (D)

Aluminium is too reactive to be extracted by reduction with carbon, so it is extracted by electrolysis of molten aluminium oxide.

Correct: (B)

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

Correct: (A)

Negative ions (anions) such as SO4^2- are attracted to the positive anode; the other ions listed are cations and move to the cathode.

Correct: (C)

Thermal decomposition takes in energy from the surroundings (it needs continuous heating), so it is endothermic.

Correct: (A)

Bonds broken = 4(410) + 2(500) = 2640 kJ. Bonds formed = 2(805) + 4(460) = 3450 kJ. ΔH = 2640 – 3450 = -810 kJ/mol.

Correct: (C)

In an endothermic reaction energy is absorbed from the surroundings, so the products store more energy than the reactants.

Correct: (D)

Energy = 200 × 4.2 × 15 = 12600 J = 12.6 kJ.

Correct: (B)

Hydrogen burns in oxygen to form only water: 2H2 + O2 → 2H2O, so burning hydrogen produces no carbon dioxide.

Correct: (C)

Cooling gives the particles less energy, so there are fewer successful collisions and the rate decreases.

Correct: (D)

A catalyst increases the rate of a reaction but is not used up; it can be recovered unchanged at the end.

Correct: (B)

With more particles in the same volume, collisions between reactant particles happen more often, so the rate increases.

Correct: (A)

Because the forward reaction is exothermic, a lower temperature shifts the equilibrium to the right, increasing the yield (although the rate becomes slower).

Correct: (B)

Copper(II) oxide loses oxygen and the copper ions gain electrons, so CuO is reduced; hydrogen is oxidised.

Correct: (A)

Reduction is the gain of electrons. Fe^3+ gains an electron to form Fe^2+; the other processes all involve loss of electrons (oxidation).

Correct: (D)

Average rate = volume / time = 30 / 15 = 2.0 cm^3/s.

Correct: (C)

Aluminium oxide is amphoteric: it reacts with both acids and alkalis. Sodium oxide is basic, and the non-metal oxides are acidic.

Correct: (D)

Strong alkalis have a pH well above 7; 0.1 mol/dm^3 sodium hydroxide has a pH of about 13.

Correct: (C)

Excess insoluble carbonate ensures that all the acid reacts; the unreacted solid carbonate is then removed by filtration.

Correct: (A)

Silver nitrate solution gives a white precipitate of silver chloride when chloride ions are present.

Correct: (B)

Ammonia is neutralised by sulfuric acid to form ammonium sulfate: 2NH3 + H2SO4 → (NH4)2SO4.

Correct: (A)

Most sulfates are soluble in water, but barium sulfate (and lead(II) sulfate) are insoluble.

Correct: (D)

Universal indicator turns purple (violet) in a strongly alkaline solution, green in a neutral solution and red in a strongly acidic solution.

Correct: (C)

Group II atoms have two electrons in their outer shell and lose both of them to form ions with a charge of +2.

Correct: (B)

Iron is found in the central block of the Periodic Table and is a transition element; sodium, aluminium and calcium are not.

Correct: (C)

Chlorine is more reactive than bromine (it is higher in Group VII), so chlorine displaces bromine from potassium bromide solution.

Correct: (B)

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

Correct: (D)

Calcium reacts vigorously with cold water to form calcium hydroxide (an alkali) and hydrogen; magnesium reacts only very slowly with cold water, and iron and copper do not react.

Correct: (A)

Zinc is above iron in the reactivity series, so it displaces iron from its salts; copper, silver and gold are all below iron.

Correct: (B)

The limestone decomposes to form calcium oxide, which reacts with impurities such as silicon dioxide (sand) to form molten slag, which is removed.

Correct: (C)

Brass is an alloy of copper and zinc; bronze is copper and tin, and steel is iron with carbon.

Correct: (A)

Air is about 78% nitrogen, 21% oxygen and 1% other gases, mainly argon and carbon dioxide.

Correct: (D)

Methane is a greenhouse gas; it traps heat in the atmosphere and contributes to climate change, as does carbon dioxide.

Correct: (D)

Water supplies are filtered to remove insoluble solids and then treated with chlorine to kill harmful microorganisms.

Correct: (A)

Butane is an alkane with four carbon atoms, so using CnH2n+2 with n = 4 gives C4H10.

Correct: (C)

Cracking breaks long-chain alkanes into shorter, more useful alkanes and alkenes, using a catalyst and high temperature.

Correct: (B)

Ethene is hydrated with steam using a phosphoric acid catalyst at about 300 °C and 60-70 atmospheres pressure.

Correct: (A)

A weak acid is only partially ionised when dissolved in water. Ethanoic acid does react with carbonates, producing carbon dioxide.

Correct: (D)

Nylon is a condensation polymer, formed when monomers join with the loss of a small molecule such as water; poly(ethene), poly(chloroethene) and poly(propene) are addition polymers.

Correct: (B)

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

Correct: (C)

Anhydrous copper(II) sulfate is white and turns blue when water is present; this is the chemical test for water.