IGCSE Chemistry Practice Test 5

Correct: (B)

Evaporation is the change from liquid to gas that takes place at the surface of a liquid at any temperature below its boiling point.

Correct: (A)

The gas with the smallest Mr diffuses fastest. Ammonia has the lowest Mr (17), so its particles move and spread the fastest.

Correct: (C)

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

Correct: (D)

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

Correct: (B)

Isotopes have the same proton number (so they are the same element) but different numbers of neutrons.

Correct: (C)

The group number equals the number of electrons in the outer shell. There are 6 outer electrons, so the element is in Group VI.

Correct: (D)

In ionic bonding the metal atom loses electrons and the non-metal atom gains them, forming oppositely charged ions that attract each other.

Correct: (B)

In diamond each carbon atom forms four strong covalent bonds to four other carbon atoms, giving a giant structure that is very hard with a very high melting point.

Correct: (A)

Methane is made of non-metal atoms only, joined by shared pairs of electrons. MgO and NaCl are ionic, and calcium has metallic bonding.

Correct: (C)

In solid sodium chloride the ions are locked in fixed positions. When molten, the ions are free to move to the electrodes and carry the charge.

Correct: (D)

The chlorine atom gains one electron to complete its outer shell, forming a Cl^- ion with the stable configuration 2,8,8.

Correct: (A)

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

Correct: (B)

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

Correct: (C)

Concentration = moles / volume in dm^3 = 0.20 / 0.500 = 0.40 mol/dm^3.

Correct: (D)

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

Correct: (A)

Moles of Mg = 2.4 / 24 = 0.10 mol. This forms 0.10 mol of MgO. Mr of MgO = 24 + 16 = 40, so mass = 0.10 × 40 = 4.0 g.

Correct: (B)

Percentage yield = (actual / theoretical) × 100 = (40 / 50) × 100 = 80%.

Correct: (C)

Moles = 36 / 18 = 2 mol.

Correct: (D)

Hydrogen ions are discharged at the cathode in preference to sodium ions because sodium is higher in the reactivity series, so hydrogen gas is produced.

Correct: (A)

Copper is below hydrogen in the reactivity series, so copper ions are discharged and a pink-brown layer of copper metal forms on the cathode.

Correct: (B)

Bromide ions are negative (anions), so they are attracted to the positive electrode, the anode, where they form bromine.

Correct: (C)

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

Correct: (D)

Cryolite dissolves the aluminium oxide and lowers the working temperature of the electrolyte, saving energy. The aluminium oxide itself melts at over 2000°C.

Correct: (A)

An exothermic reaction gives out energy to the surroundings, so the temperature of the surroundings rises.

Correct: (B)

Energy taken in breaking bonds = 436 + 242 = 678 kJ. Energy given out forming bonds = 2 × 431 = 862 kJ. Energy change = 678 – 862 = -184 kJ/mol.

Correct: (C)

Thermal decomposition requires continuous heating because it takes in energy. Burning and neutralisation are exothermic, and freezing gives out energy.

Correct: (D)

In the fuel cell hydrogen reacts with oxygen to form water, exactly as when hydrogen burns in oxygen, but the energy is released as electricity.

Correct: (A)

The activation energy is the minimum energy particles need to react, shown as the gap between the reactant level and the peak of the barrier.

Correct: (B)

At a higher temperature the particles move faster, collide more often, and a much larger fraction of the collisions have enough energy to react.

Correct: (C)

A catalyst speeds up a reaction by providing a different route with a lower activation energy, and it is chemically unchanged at the end.

Correct: (D)

The reaction produces carbon dioxide gas, so collecting and measuring the gas volume at regular time intervals gives the rate directly.

Correct: (A)

Copper(II) sulfate dehydration is a classic reversible reaction: heating drives off the water and adding water reverses the change. The others go to completion.

Correct: (B)

The Haber process uses about 450°C as a compromise temperature, about 200 atm pressure, and an iron catalyst.

Correct: (C)

Zinc atoms lose electrons to form Zn^2+ ions, so zinc is oxidised. The copper(II) ions gain electrons and are reduced.

Correct: (D)

Oxygen gains electrons from magnesium, causing magnesium to be oxidised, so oxygen is the oxidising agent (and is itself reduced).

Correct: (A)

Strong acids fully ionise in solution and have very low pH values, around pH 1 for a concentrated laboratory acid.

Correct: (B)

Acid + carbonate → salt + water + carbon dioxide. Here the salt formed is magnesium sulfate.

Correct: (C)

An alkali is a base that dissolves in water, releasing OH^- ions into the solution, giving a pH above 7.

Correct: (D)

Barium sulfate is insoluble, so it is made by precipitation: mixing two solutions containing Ba^2+ and SO4^2- ions forms the solid salt immediately.

Correct: (A)

An oxide that reacts with both acids and alkalis is amphoteric. Aluminium oxide and zinc oxide are the standard examples.

Correct: (B)

Ba^2+ ions react with sulfate ions to give a white precipitate of barium sulfate, which stays insoluble when dilute hydrochloric acid is added.

Correct: (C)

Sodium hydroxide is a strong alkali (pH about 13-14), so universal indicator turns blue to purple.

Correct: (D)

Group I metals become more reactive down the group because the outer electron is further from the nucleus and is lost more easily.

Correct: (A)

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

Correct: (C)

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

Correct: (B)

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

Correct: (D)

Potassium is the most reactive of the four metals listed, so it displaces copper, iron and zinc from their compounds.

Correct: (A)

Coke burns to form carbon monoxide, which reduces the iron(III) oxide: Fe2O3 + 3CO → 2Fe + 3CO2.

Correct: (B)

Rusting needs both air (oxygen) and water together. Painting, oiling or coating the iron works by keeping these away from the surface.

Correct: (C)

In an alloy the different-sized atoms disrupt the regular layers, so the layers cannot slide over each other as easily, making the alloy harder and stronger.

Correct: (A)

Chlorination sterilises the water by killing bacteria and other microorganisms that could cause disease.

Correct: (C)

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

Correct: (B)

Fertilisers supply nitrogen, phosphorus and potassium (NPK). Ammonium nitrate, NH4NO3, is valued for its high nitrogen content.

Correct: (C)

Alkanes are saturated hydrocarbons with general formula CnH2n+2, e.g. methane CH4 and ethane C2H6.

Correct: (D)

Ethene is unsaturated and undergoes addition with bromine, decolourising the orange bromine water. Ethane, being saturated, does not react.

Correct: (A)

Fermentation works best at about 37°C (warm, so the yeast enzymes are not denatured), with yeast, and anaerobic conditions so ethanol is not oxidised further.

Correct: (B)

Addition polymerisation joins many alkene monomer molecules together with no other product formed; the C=C bonds open up to link the units.

Correct: (C)

Carboxylic acids react with alcohols to form esters: ethanoic acid + ethanol ⇌ ethyl ethanoate + water. This is esterification.

Correct: (D)

Rf = distance moved by the spot / distance moved by the solvent = 4.0 / 8.0 = 0.5.

Correct: (C)

Silver nitrate in the presence of dilute nitric acid gives a white precipitate of silver chloride if chloride ions are present.