Metals and Non-Metals: Properties, Ores and Alloys

The correct answer is C, zinc. Calamine is zinc carbonate, and since it is a carbonate ore it is converted to the oxide by calcination, that is by heating in the absence of air, before being reduced to the metal. The other important ore of zinc is zinc blende, which is the sulphide and is roasted rather than calcined. Option A is wrong because the chief ore of tin is cassiterite, the oxide. Option B is wrong because magnesium is obtained from magnesite, dolomite and from sea water as its chloride. Option D is wrong because copper comes mainly from copper pyrites, also called chalcopyrite, and from cuprite. A pair of definitions is worth keeping ready for this topic: calcination is heating a carbonate ore without air, while roasting is heating a sulphide ore in air, and both give the oxide.

The correct answer is B, silver. Silver is an element, a pure metal with its own place in the periodic table, so it cannot be an alloy; an alloy is a homogeneous mixture of two or more metals, or of a metal with a non-metal such as carbon. Option A, solder, is an alloy of lead and tin, valued for its low melting point when joining electrical wires. Option C, bronze, is an alloy of copper and tin, the metal that gave its name to an age of human history. Option D, brass, is an alloy of copper and zinc, used for utensils, fittings and musical instruments. The trap here is German silver, which contains copper, zinc and nickel and no silver at all, so it is an alloy despite its name, while silver itself is not.

The correct answer is A, gold. Ductility is the property of being drawn into a wire, and gold is the most ductile metal known; it is also the most malleable, so a very small quantity can be beaten into an extremely thin sheet or drawn into a very long wire. Option C, silver, is the next most ductile and is the best conductor of both heat and electricity, which is why it is easy to confuse the two superlatives; remember that silver leads in conduction while gold leads in ductility and malleability. Option B, copper, is ductile enough to be drawn into the wires used in household wiring, but far less so than gold. Option D, iron, is ductile when hot but comparatively hard and is valued for strength rather than for being drawn out.

The correct answer is D, copper and zinc. Brass takes the workability of copper and the hardness of zinc, resists corrosion and is easy to cast, which is why it is used for utensils, locks, taps, fittings and wind instruments. Option A, copper and tin, is bronze, and the brass and bronze pair is the single most frequently confused item in this chapter, so fix zinc with brass and tin with bronze. Option B, copper and nickel, is cupronickel, used in coins and in condenser tubes. Option C, copper and iron, is not a standard alloy of this kind, though iron and copper occur together in the ore copper pyrites. Related alloys are worth learning with these: German silver is copper, zinc and nickel; gun metal is copper, tin and zinc; and bell metal is copper with a larger proportion of tin.

The correct answer is B, mercury. Mercury is the only metal that is liquid at ordinary room temperature, which is why it was long used in thermometers and barometers; it is also the metal that forms amalgams, alloys in which mercury is one component. Option A, sodium, is a solid, although a very soft one that can be cut with a knife and must be stored under kerosene because it reacts violently with air and water. Option C, lead, is a soft, dense solid with a low melting point, but it is far from liquid at room temperature. Option D, tungsten, has the highest melting point of the metals, which is exactly why it is used for the filament of an incandescent lamp. Among non-metals, bromine is the one that is liquid at room temperature, and gallium and caesium are metals that melt in the warmth of the hand.

The correct answer is C, 3:1. Aqua regia is three parts concentrated hydrochloric acid to one part concentrated nitric acid, and the name means royal water, given because the mixture attacks the noble metals gold and platinum, which neither acid can dissolve on its own. Option B, 1:3, is the same pair of acids in the reverse order and is the commonest wrong answer, so note that the larger share is hydrochloric acid. Options A and D do not correspond to any standard laboratory reagent of this kind. The chemistry is worth one line: nitric acid oxidises the gold and the chloride from hydrochloric acid holds the resulting ions in solution, so each acid does what the other cannot. Aqua regia is used to test the purity of gold and to recover precious metals.

The correct answer is C, silver. Silver has the highest electrical conductivity of all metals and also the highest thermal conductivity, but it is costly and tarnishes, so it is used only in specialised contacts and instruments. Option A, copper, comes next and is the metal actually used for household and industrial wiring, because it combines high conductivity with reasonable cost and good ductility; students who answer from everyday use rather than from the property pick this one. Option B, aluminium, is a lighter and cheaper conductor used for overhead transmission lines, where weight matters more than conductivity per unit area. Option D, gold, conducts well and does not corrode, so it is used to plate delicate electronic contacts, but it ranks below silver and copper. Remember the order: silver, then copper, then gold, then aluminium.

The correct answer is A, lead. Galena is lead sulphide, the principal ore from which lead is obtained; being a sulphide it is concentrated by froth flotation and then roasted in air to the oxide before reduction. Option B, mercury, is obtained from cinnabar, which is mercury sulphide, and the two sulphides are often placed together in matching questions. Option C, aluminium, comes from bauxite, a hydrated oxide, and because aluminium is highly reactive the oxide is reduced by electrolysis rather than by carbon. Option D, iron, comes from haematite and magnetite, both oxides, and magnetite is the one separated magnetically. A short list is worth memorising in ore-and-metal pairs: galena for lead, cinnabar for mercury, bauxite for aluminium, calamine and zinc blende for zinc, and copper pyrites for copper.

The correct answer is B, zinc. In galvanisation iron or steel is given a coating of zinc, usually by dipping it in the molten metal, and the coating protects the iron in two ways: it keeps out air and moisture, and because zinc is more reactive than iron it corrodes in place of the iron even where the coating has been scratched. Option A, tin, is used to coat steel in the tinplate of food cans, a process called tinning, which protects only while the coating is intact. Option C, chromium, is applied by electroplating for shine and corrosion resistance and is also alloyed into stainless steel along with nickel. Option D, nickel, is likewise an electroplating and alloying metal. Recall that rusting needs both oxygen and moisture, so a coating, paint, oil or grease that keeps either away prevents it.

The correct answer is B, aluminium oxide. An amphoteric oxide reacts with both acids and bases to form salts, and aluminium oxide does exactly that, behaving as a base towards hydrochloric acid and as an acid towards sodium hydroxide; zinc oxide is the other amphoteric oxide asked in examinations. Option A, sodium oxide, is a typical metal oxide and therefore basic, dissolving in water to give sodium hydroxide, a strong alkali. Option C, carbon dioxide, is a non-metal oxide and therefore acidic, dissolving in water to give carbonic acid, which is why it turns moist blue litmus red. Option D, sulphur dioxide, is likewise acidic and gives sulphurous acid in water. Remember the rule and its two exceptions: metal oxides are basic, non-metal oxides are acidic, and the oxides of aluminium and zinc are amphoteric.

The correct answer is B, graphite. Graphite is an allotrope of carbon in which each atom is bonded to three others, leaving one electron per atom free to move through the layers, so it conducts electricity although it is a non-metal; this is why graphite is used for electrodes and in dry cells. Option A, sulphur, is a brittle, non-conducting solid, the standard example of non-metallic behaviour. Option C, phosphorus, does not conduct and its white form is stored under water because it ignites in air. Option D, iodine, is the non-metal that is lustrous, so it is the exception to a different rule and a favourite distractor here. Note also diamond, the other allotrope of carbon: it is the hardest natural substance and conducts heat extremely well, but it does not conduct electricity.