Chapter 3: Metals and Non-metals (Chemistry)

(i) Mercury (ii) Sodium (or potassium, lithium) (iii) Silver (then copper) (iv) Lead (or mercury)

• Malleable: can be beaten into thin sheets without breaking. Gold and silver are the most malleable metals; aluminium foil is an everyday example.
• Ductile: can be drawn into thin wires. Gold is the most ductile metal; copper and aluminium are drawn into electric wires.

Malleable: can be hammered into sheets. Ductile: can be drawn into wires.

Sodium is so reactive that it catches fire if kept in open air, reacting vigorously with oxygen and moisture. Kerosene does not react with sodium and keeps air and water away from it, which prevents accidental fires.

Because it reacts violently with air and water; kerosene keeps it away from both.

1. $3\mathrm{Fe}(\mathrm{s})+4\mathrm{H}{}_2\mathrm{O}(\mathrm{g})\to \mathrm{Fe}{}_3\mathrm{O}{}_4(\mathrm{s})+4\mathrm{H}{}_2(\mathrm{g})$
2. $\mathrm{Ca}(\mathrm{s})+2\mathrm{H}{}_2\mathrm{O}(\mathrm{l})\to \mathrm{Ca}(\mathrm{OH}){}_2(\mathrm{aq})+\mathrm{H}{}_2(\mathrm{g})$ and $2\mathrm{K}(\mathrm{s})+2\mathrm{H}{}_2\mathrm{O}(\mathrm{l})\to 2\mathrm{KOH}(\mathrm{aq})+\mathrm{H}{}_2(\mathrm{g})$ + heat (so much heat that the hydrogen catches fire)

See the equations above.

• B displaces iron, so it is more reactive than iron (but less than zinc).
• A displaces copper but not iron, so it lies between iron and copper.
• C displaces only silver, so it lies between copper and silver.
• D displaces nothing, so it is below silver.

1. B is the most reactive.
2. B is more reactive than iron, so it is certainly more reactive than copper. It will displace copper: the blue colour of the solution fades and a reddish-brown layer of copper is deposited on B.
3. B > A > C > D

(i) B (ii) Copper is displaced: the blue colour fades and reddish-brown copper deposits. (iii) B > A > C > D

Hydrogen gas.

$\mathrm{Fe}(\mathrm{s})+\mathrm{H}{}_2\mathrm{SO}{}_4(\mathrm{aq})\to \mathrm{FeSO}{}_4(\mathrm{aq})+\mathrm{H}{}_2(\mathrm{g})$

Hydrogen; Fe + H₂SO₄ → FeSO₄ + H₂

Zinc is more reactive than iron, so it displaces iron. The pale green solution turns colourless, and a dark grey deposit of iron forms on the zinc.

$\mathrm{Zn}(\mathrm{s})+\mathrm{FeSO}{}_4(\mathrm{aq})\to \mathrm{ZnSO}{}_4(\mathrm{aq})+\mathrm{Fe}(\mathrm{s})$

The green colour fades and iron is deposited: Zn + FeSO₄ → ZnSO₄ + Fe

(i) Only the valence (outermost) electrons are shown as dots:

(ii) Each sodium atom gives its one electron to oxygen; magnesium gives both its electrons to one oxygen atom. Oxygen then has a complete octet.

$$\mathrm{Na}\cdot +\cdot \stackrel{\cdot \cdot }{\underset{\cdot \cdot }{\mathrm{O}}}\cdot +\cdot \mathrm{Na}⟶{\mathrm{Na}}^{+}{\left[:\stackrel{\cdot \cdot }{\underset{\cdot \cdot }{\mathrm{O}}}:\right]}^{2-}{\mathrm{Na}}^{+}(\mathrm{Na}{}_2\mathrm{O})$$

$$\cdot \mathrm{Mg}\cdot +\cdot \stackrel{\cdot \cdot }{\underset{\cdot \cdot }{\mathrm{O}}}\cdot ⟶{\mathrm{Mg}}^{2+}{\left[:\stackrel{\cdot \cdot }{\underset{\cdot \cdot }{\mathrm{O}}}:\right]}^{2-}(\mathrm{MgO})$$

(iii) Na₂O contains sodium ions ($\mathrm{Na}{}^{+}$) and oxide ions ($\mathrm{O}{}^{2-}$); MgO contains magnesium ions ($\mathrm{Mg}{}^{2+}$) and oxide ions ($\mathrm{O}{}^{2-}$).

(iii) Na₂O: Na⁺ and O²⁻; MgO: Mg²⁺ and O²⁻

In an ionic compound, oppositely charged ions are held together by strong electrostatic forces of attraction in a lattice. A large amount of energy is needed to overcome these forces, so ionic compounds melt and boil at high temperatures.

Because of the strong forces of attraction between their oppositely charged ions.

1. Mineral: an element or compound that occurs naturally in the earth's crust.
2. Ore: a mineral from which a metal can be extracted profitably, because it contains a high percentage of that metal.
3. Gangue: the impurities, such as soil and sand, present in the ore as mined. They are removed before the metal is extracted.

See the definitions above.

Gold and platinum (silver and copper are also sometimes found free).

Reduction. The oxide is heated with a reducing agent such as carbon (coke), e.g. $\mathrm{ZnO}+\mathrm{C}\to \mathrm{Zn}+\mathrm{CO}$, or with a more reactive metal (displacement), e.g. $\mathrm{Fe}{}_2\mathrm{O}{}_3+2\mathrm{Al}\to 2\mathrm{Fe}+\mathrm{Al}{}_2\mathrm{O}{}_3$. Highly reactive metals are obtained by electrolytic reduction.

Reduction (with carbon, a more reactive metal, or electrolysis).

A metal displaces another metal from its oxide only if it is more reactive. The order is Mg > Zn > Cu.

Magnesium with zinc oxide, zinc with copper oxide and magnesium with copper oxide.

Metals low in the reactivity series, such as gold, platinum and silver (silver tarnishes slowly but does not corrode away), do not corrode easily. Aluminium resists corrosion too, because of its protective oxide layer.

Gold, platinum (and other less reactive metals).

An alloy is a homogeneous mixture of two or more metals, or of a metal and a non-metal, made by melting them together. Examples: steel (iron and carbon), brass (copper and zinc), bronze (copper and tin), solder (lead and tin).

Homogeneous mixtures of a metal with other metals or a non-metal, e.g. brass, bronze, steel.

Only copper is more reactive than the metal in the salt (silver): $\mathrm{Cu}+2\mathrm{AgNO}{}_3\to \mathrm{Cu}(\mathrm{NO}{}_3){}_2+2\mathrm{Ag}$.

(d) AgNO₃ solution and copper metal

A frying pan is heated and touches food, so grease and paint (which would burn off or get into the food) are not suitable. A zinc coating (galvanisation) protects it.

(c) Applying a coating of zinc

Calcium oxide is an ionic compound (high melting point) and dissolves in water to form calcium hydroxide. Carbon gives a gas, silica is insoluble, and iron oxide is insoluble.

(a) calcium

Zinc is more reactive and could react with acids in the food to form harmful compounds; tin is less reactive.

(c) zinc is more reactive than tin.

1. Malleability test: beat each sample with the hammer. Metals flatten into sheets; non-metals such as sulphur or coal break into powder. Conductivity test: connect each sample in a circuit with the battery, bulb and switch. If the bulb glows, the sample is a metal; if not, it is a non-metal.
2. The tests are useful but not foolproof. Graphite (a non-metal) conducts electricity, and some metals are soft or brittle. Using both tests together gives a reliable answer for most samples.

Metals flatten when hammered and conduct electricity; non-metals break and do not conduct. Exceptions such as graphite mean both tests should be used.

Metal oxides that react with both acids and bases to form salt and water are called amphoteric oxides. Examples: aluminium oxide (Al₂O₃) and zinc oxide (ZnO).

• $\mathrm{Al}{}_2\mathrm{O}{}_3+6\mathrm{HCl}\to 2\mathrm{AlCl}{}_3+3\mathrm{H}{}_2\mathrm{O}$ (acting as a base)
• $\mathrm{Al}{}_2\mathrm{O}{}_3+2\mathrm{NaOH}\to 2\mathrm{NaAlO}{}_2+\mathrm{H}{}_2\mathrm{O}$ (acting as an acid)

Oxides that react with both acids and bases, e.g. Al₂O₃ and ZnO.

Metals above hydrogen in the reactivity series displace hydrogen; those below it do not.

Will: zinc and magnesium (also iron, aluminium). Will not: copper and silver (also gold).

• Anode: a thick block of the impure metal M
• Cathode: a thin strip of the pure metal M
• Electrolyte: a solution of a soluble salt of M (e.g. acidified copper sulphate for copper)

When current passes, pure metal from the anode dissolves and deposits on the cathode, while impurities settle below the anode as anode mud.

Anode: impure M; cathode: pure M; electrolyte: a solution of a salt of M.

1. (i) No change: without water the gas cannot form an acid. (ii) Moist blue litmus turns red, because sulphur dioxide dissolves in the water to form sulphurous acid.
2. $\mathrm{S}(\mathrm{s})+\mathrm{O}{}_2(\mathrm{g})\to \mathrm{SO}{}_2(\mathrm{g})$, and with water $\mathrm{SO}{}_2+\mathrm{H}{}_2\mathrm{O}\to \mathrm{H}{}_2\mathrm{SO}{}_3$

(a) (i) No effect (ii) Blue litmus turns red. (b) S + O₂ → SO₂

• Painting, oiling or greasing it, which keeps air and moisture away
• Galvanising: coating it with a thin layer of zinc

(Making alloys such as stainless steel, and chrome plating, are other methods.)

Painting or greasing, and galvanising with zinc.

Non-metals form acidic oxides (e.g. SO₂ and CO₂, which turn blue litmus red in solution) or neutral oxides (e.g. CO and H₂O).

Acidic or neutral oxides.

1. They are lustrous, malleable and ductile, and being very unreactive they do not corrode or tarnish easily.
2. They are so reactive that they react vigorously with oxygen and moisture in air and can catch fire. Oil keeps air and water away.
3. Aluminium is light, a good conductor of heat, and resistant to corrosion because a thin protective layer of aluminium oxide forms on its surface and stops further reaction.
4. It is easier to obtain a metal from its oxide than from its carbonate or sulphide. So carbonate ores are calcined (heated without air) and sulphide ores are roasted (heated in air) to form oxides, which are then reduced.

See the reasons above.

A copper vessel tarnishes when it gets a green coating of basic copper carbonate (CuCO₃·Cu(OH)₂). This coating is basic. Lemon and tamarind contain acids, which neutralise and dissolve the coating, leaving the shiny copper surface again.

The acids in them dissolve the basic copper carbonate layer on the copper.

See the table above.

He used aqua regia, a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio 3 : 1. It is one of the few reagents that can dissolve gold. It dissolved the outer layer of the bangles, exposing shiny gold underneath, and he kept the dissolved gold.

Aqua regia (3 parts conc. HCl to 1 part conc. HNO₃), which dissolves gold.

Copper is a better conductor of heat and does not react with hot water or steam, so it does not corrode. Steel contains iron, which reacts with hot water and steam and rusts, so the tank would corrode.

Copper conducts heat well and does not react with water, while iron in steel corrodes in hot water.