IGCSE Chemistry Practice Test 10

Correct: (C)

Sublimation is the change of state in which a solid changes directly into a gas without becoming a liquid.

Correct: (B)

During boiling, the energy supplied is used to break the forces holding the liquid particles together, so the temperature stays constant until all the liquid has changed to gas.

Correct: (A)

Compressing the gas makes the particles closer together, so they hit the walls more often, increasing the pressure. At constant temperature their speed does not change.

Correct: (C)

The proton number is 8. The mass number = protons + neutrons = 8 + 8 = 16.

Correct: (C)

The group number equals the number of electrons in the outer shell. Chlorine has 7 outer electrons, so it is in Group VII.

Correct: (A)

The sodium atom loses its single outer electron to form Na^+, leaving the configuration 2,8.

Correct: (D)

In the giant ionic lattice every ion is strongly attracted to oppositely charged ions around it, so a lot of energy is needed to melt the solid.

Correct: (B)

Melting a simple molecular solid only overcomes the weak intermolecular forces; the strong covalent bonds within each molecule are not broken.

Correct: (A)

In graphite each carbon atom bonds to three others, so one electron per atom is delocalised and free to carry charge along the layers.

Correct: (B)

Two chloride ions (total charge 2-) are needed to balance one Mg^2+ ion, giving the formula MgCl2.

Correct: (D)

A covalent bond consists of a pair of electrons shared between two atoms, usually non-metals.

Correct: (A)

Moles = mass / Mr = 4.0 / 40 = 0.1 mol.

Correct: (C)

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

Correct: (C)

Concentration = moles / volume in dm^3 = 0.50 / 0.250 = 2.0 mol/dm^3.

Correct: (D)

The equation shows 1 volume of methane reacts with 2 volumes of oxygen, so 10 cm^3 of methane needs 20 cm^3 of oxygen.

Correct: (C)

The empirical formula mass is 12 + 2 = 14. 42 / 14 = 3, so the molecular formula is 3 × CH2 = C3H6.

Correct: (C)

Percentage purity = (mass of pure substance / mass of sample) × 100 = (9.0 / 10.0) × 100 = 90%.

Correct: (A)

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

Correct: (D)

Aluminium ions, Al^3+, are positive and move to the negative cathode, where they gain electrons and form aluminium metal.

Correct: (A)

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

Correct: (A)

Opposite charges attract: negative anions move to the positive electrode, which is called the anode.

Correct: (B)

The object to be plated is connected as the cathode (negative), and the electrolyte must contain ions of the plating metal, here Cu^2+ ions.

Correct: (B)

Metals more reactive than carbon, such as aluminium, cannot be extracted by reduction with carbon, so electrolysis of the molten ore is used.

Correct: (D)

A fall in temperature means energy has been absorbed from the surroundings (the water), so the process is endothermic.

Correct: (B)

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

Correct: (C)

Combustion releases energy to the surroundings and is exothermic. Decomposition of limestone, photosynthesis and dissolving ammonium nitrate are endothermic.

Correct: (A)

In an exothermic reaction energy is released, so the products are at a lower energy level than the reactants and ΔH is negative.

Correct: (B)

A fuel cell reacts hydrogen with oxygen to form water and converts the chemical energy directly into electricity; it is not a combustion engine and is not recharged.

Correct: (D)

Powder exposes a much larger surface area than chips, so collisions occur more frequently and the rate increases.

Correct: (B)

Recording the volume of hydrogen produced at regular intervals allows the rate to be calculated; the reaction has no colour change to observe.

Correct: (A)

At equilibrium both reactions still occur but at equal rates, so the amounts of reactants and products no longer change.

Correct: (B)

The forward reaction is exothermic, so lower temperatures favour yield but slow the rate too much; 450°C is a compromise between rate and yield.

Correct: (D)

Reduction is the loss of oxygen (or gain of electrons). CuO loses oxygen to form copper, while hydrogen is oxidised.

Correct: (C)

A catalyst speeds up the forward and reverse reactions by the same amount, so equilibrium is reached faster but its position is unchanged.

Correct: (B)

Increasing the pressure squashes the gas particles into a smaller volume, increasing their concentration and the frequency of collisions.

Correct: (A)

Acid + alkali → salt + water. This is the defining neutralisation reaction.

Correct: (D)

Insoluble salts are made by precipitation: mix two solutions containing the required ions, then filter, wash and dry the precipitate.

Correct: (A)

Nitrate ions are reduced by aluminium in alkaline solution to ammonia, which is an alkaline gas and turns damp red litmus blue.

Correct: (C)

Sulfur dioxide is a non-metal oxide and is acidic; it reacts with alkalis. The other three are basic metal oxides.

Correct: (D)

Universal Indicator turns purple only in strongly alkaline solutions (about pH 14); strong acids turn it red and neutral solutions turn it green.

Correct: (C)

Ammonia + sulfuric acid → ammonium sulfate. (Ammonia with nitric acid gives ammonium nitrate; with hydrochloric acid it gives ammonium chloride.)

Correct: (D)

Magnesium reacts with the acid to form magnesium chloride and hydrogen. Hydrogen is identified by the squeaky pop with a lighted splint.

Correct: (C)

Down Group VII the melting and boiling points increase: chlorine is a gas, bromine is a liquid and iodine is a solid at room temperature.

Correct: (A)

A more reactive halogen displaces a less reactive one. Bromine is more reactive than iodine, so bromine displaces iodine from potassium iodide. Iodine cannot displace chlorine or bromine, and chlorine cannot displace fluorine.

Correct: (B)

Transition elements and their compounds commonly act as catalysts; iron and vanadium(V) oxide are both from the transition block.

Correct: (D)

Chemical properties are controlled by the outer-shell electrons; elements in a group have the same number of these, so they react in similar ways.

Correct: (D)

In the reactivity series magnesium is above zinc, iron and copper, so it is the most reactive of the four.

Correct: (B)

Zinc is more reactive than copper, so it displaces copper: Zn + CuSO4 → ZnSO4 + Cu. The blue colour fades as Cu^2+ ions leave the solution.

Correct: (B)

Aluminium is light (low density) for its strength and its surface forms a protective oxide layer that prevents further corrosion, ideal for aircraft.

Correct: (A)

Stainless steel is an alloy of iron with chromium (and nickel); the chromium forms a protective layer so the steel resists rusting. Iron coated with zinc is galvanised steel.

Correct: (D)

Filtration (through sand and gravel beds) removes insoluble solids; chlorine is then added to kill microorganisms.

Correct: (C)

Clean dry air is about 78% nitrogen, 21% oxygen and about 1% other gases including argon and carbon dioxide (about 0.04%).

Correct: (C)

Photosynthesis uses carbon dioxide from the air to make glucose. Combustion, respiration and limestone decomposition all release carbon dioxide.

Correct: (B)

Alkenes are unsaturated hydrocarbons containing one C=C bond, with the general formula CnH2n.

Correct: (A)

Cracking breaks down long-chain alkanes into more useful short-chain alkanes and alkenes; it needs a high temperature and a catalyst such as aluminium oxide. Separation by boiling point is fractional distillation.

Correct: (B)

Microorganisms in the air oxidise ethanol to ethanoic acid (the acid in vinegar), which tastes sour.

Correct: (A)

Carboxylic acid + alcohol → ester + water. Ethanoic acid + ethanol → ethyl ethanoate + water.

Correct: (C)

In condensation polymerisation each new bond formed eliminates a small molecule, usually water; this is how polyesters such as Terylene are made.

Correct: (D)

Carbonates react with acids to give carbon dioxide, which turns limewater milky. This is the standard test for a carbonate.

Correct: (D)

Rf = 6.0 / 8.0 = 0.75. A pure substance produces a single spot in any given solvent, while a mixture gives two or more spots.