IGCSE Chemistry Practice Test 19

Correct: (B)

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

Correct: (D)

25°C is above the melting point but below the boiling point, so the substance is a liquid.

Correct: (A)

On melting, particles gain enough energy to overcome some attractive forces and move around, while the temperature stays constant.

Correct: (C)

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

Correct: (B)

Magnesium has 12 electrons arranged as 2 in the first shell, 8 in the second and 2 in the third: 2,8,2.

Correct: (A)

Isotopes have the same proton number (so they are the same element) but different neutron numbers and therefore different mass numbers.

Correct: (D)

In diamond every carbon atom is covalently bonded to four others in one giant lattice, giving a very high melting point.

Correct: (C)

Sodium chloride is ionic; its ions are locked in place in the solid but are free to move and carry charge when molten.

Correct: (B)

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

Correct: (D)

The atom gains one electron to complete its outer shell, forming a 1- ion.

Correct: (A)

In metals the layers of positive ions can slide over each other, so metals are malleable and ductile.

Correct: (C)

Mr = 40 + 12 + (3 × 16) = 100.

Correct: (A)

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

Correct: (B)

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

Correct: (D)

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

Correct: (C)

250 cm^3 = 0.250 dm^3, so concentration = 0.10 / 0.250 = 0.40 mol/dm^3.

Correct: (B)

Percentage yield = (actual / theoretical) × 100 = (30 / 40) × 100 = 75%.

Correct: (A)

Moles of Mg = 4.8 / 24 = 0.20 mol, so 0.20 mol of H2 forms. Volume = 0.20 × 24 = 4.8 dm^3.

Correct: (D)

Lead(II) ions are positively charged, so they move to the cathode where they gain electrons and form lead metal.

Correct: (C)

At the anode, hydroxide ions from the water are discharged to form oxygen gas.

Correct: (A)

In concentrated solution, chloride ions are discharged at the anode to form chlorine gas.

Correct: (B)

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

Correct: (D)

Zinc is more reactive than copper, so zinc atoms lose electrons (are oxidised) and electrons flow through the wires to the copper electrode.

Correct: (A)

Combustion releases energy to the surroundings as heat, so it is exothermic. The others take in energy.

Correct: (C)

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

Correct: (B)

An endothermic reaction absorbs energy from the surroundings, so the temperature of the surroundings falls.

Correct: (D)

Hydrogen burns in oxygen to form only water: 2H2 + O2 → 2H2O.

Correct: (A)

In an exothermic reaction the products have less energy than the reactants, energy is released, and ΔH is negative.

Correct: (C)

A higher concentration means more particles in the same volume, so collisions are more frequent and the rate increases.

Correct: (B)

A catalyst provides a different reaction pathway with lower activation energy, so more collisions are successful. It is not used up.

Correct: (D)

There are 4 moles of gas on the left and 2 on the right, so higher pressure shifts the equilibrium towards ammonia, increasing the yield.

Correct: (A)

Oxidation is loss of electrons (OILRIG); reduction is gain of electrons.

Correct: (C)

Cu^2+ ions gain electrons from zinc and are reduced, so Cu^2+ ions are the oxidising agent. Zinc is the reducing agent.

Correct: (B)

A gas syringe collects and measures the volume of gas given off as the reaction proceeds.

Correct: (D)

At equilibrium both reactions continue at equal rates, so the concentrations of reactants and products stay constant.

Correct: (A)

pH 13 is strongly alkaline; pH 7 is neutral, and values below 7 are acidic.

Correct: (C)

Acid + carbonate → salt + water + carbon dioxide.

Correct: (B)

Sulfur dioxide is the oxide of a non-metal and is acidic; the others are metal oxides and are basic.

Correct: (D)

The insoluble oxide is added in excess to warm acid, the excess is filtered off, and the filtrate is crystallised to give pure zinc sulfate crystals.

Correct: (A)

Barium chloride (after acidifying with dilute hydrochloric acid) gives a white precipitate of barium sulfate if sulfate ions are present.

Correct: (C)

Barium sulfate is insoluble, so it is prepared by mixing solutions of soluble barium and sulfate salts and filtering off the precipitate.

Correct: (B)

Ammonium salts react with alkalis on warming to release ammonia gas, which turns damp red litmus paper blue.

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)

Reactivity of the halogens decreases down the group, so chlorine is more reactive than bromine and iodine and displaces them from their salts.

Correct: (C)

Transition elements have high melting points and densities, form coloured compounds and often act as catalysts.

Correct: (B)

The atom has 5 electrons in its outer shell, so it is in Group 15 (Group V). It is phosphorus.

Correct: (D)

Of these metals, zinc is highest in the reactivity series and reacts most vigorously with dilute acid; copper and silver do not react.

Correct: (A)

Aluminium is above carbon in the reactivity series, so it is extracted by electrolysis of molten aluminium oxide dissolved in cryolite.

Correct: (C)

Iron rusts only when both air (oxygen) and water are present; experiments with boiled water or dry air show no rusting.

Correct: (B)

Brass is a mixture of copper and zinc; bronze is copper and tin.

Correct: (D)

Chlorine is added to water supplies to kill microbes and make the water safe to drink.

Correct: (A)

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

Correct: (C)

Methane and carbon dioxide are greenhouse gases that absorb infrared radiation and contribute to global warming.

Correct: (B)

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

Correct: (D)

The C=C double bond in ethene reacts with bromine in an addition reaction, removing the orange colour.

Correct: (C)

Fermentation uses yeast enzymes at around 30°C without air: glucose → ethanol + carbon dioxide.

Correct: (C)

Many ethene monomers join together to form poly(ethene), a plastic used for bags and bottles.

Correct: (B)

Carboxylic acids such as ethanoic acid contain the -COOH functional group, which makes them weak acids.

Correct: (D)

Silver nitrate solution, acidified with dilute nitric acid, gives a white precipitate of silver chloride if chloride ions are present.

Correct: (A)

A pure solid melts sharply at one temperature; impurities lower the melting point and make it melt over a range.