Metals, Non-metals and Carbon Compounds
The reactivity series and displacement
The reactivity series ranks metals by how readily they lose electrons. In Class 10 order, from most to least reactive: K, Na, Ca, Mg, Al, Zn, Fe, Pb, [H], Cu, Hg, Ag, Au. A metal displaces from solution any metal below it, never one above it.
| Metal added | Solution | Result |
|---|---|---|
| Fe | CuSO₄ | Fe + CuSO₄ → FeSO₄ + Cu (Fe is above Cu) |
| Zn | FeSO₄ | Zn + FeSO₄ → ZnSO₄ + Fe (Zn is above Fe) |
| Cu | AgNO₃ | Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag (Cu is above Ag) |
| Cu | ZnSO₄ | No reaction (Cu is below Zn) |
| Pb | CuCl₂ | Pb + CuCl₂ → PbCl₂ + Cu (Pb is above Cu) |
Extraction of metals
A mineral is a naturally occurring compound of a metal; an ore is a mineral from which the metal can be extracted profitably; the earthy impurity is gangue. After the ore is concentrated, the method depends on the position in the series. Examples of ores: bauxite (aluminium), haematite (iron), cinnabar HgS (mercury), copper glance Cu₂S, zinc blende ZnS and galena PbS. Copper glance is a special case: roasting it in a limited supply of air gives copper directly, 2Cu₂S + 3O₂ → 2Cu₂O + 2SO₂, then 2Cu₂O + Cu₂S → 6Cu + SO₂.
| Group | Method | Example |
|---|---|---|
| K, Na, Ca, Mg, Al (top) | Electrolytic reduction of the molten chloride or oxide; the metal collects at the cathode | NaCl → Na at the cathode and Cl₂ at the anode |
| Zn, Fe, Pb, Cu (middle) | Sulphide is roasted to oxide; carbonate is calcined to oxide; oxide is reduced with carbon | 2ZnS + 3O₂ → 2ZnO + 2SO₂; ZnO + C → Zn + CO |
| Hg, Ag, Au (bottom) | Heating alone is enough for the oxide or sulphide | 2HgS + 3O₂ → 2HgO + 2SO₂; 2HgO → 2Hg + O₂ |
Roasting heats a sulphide ore strongly in excess air; calcination heats a carbonate ore in limited air. The thermit reaction, Fe₂O₃ + 2Al → 2Fe + Al₂O₃ + heat, is a displacement in which aluminium is the reducing agent. It releases so much heat that the iron is molten, and this is used to weld railway tracks and to repair cracks in heavy machine parts. Electrolytic refining purifies metals such as copper: the impure metal is the anode, a strip of pure metal is the cathode and the electrolyte is an acidified solution of the metal's salt (copper sulphate for copper). Pure metal deposits on the cathode and the insoluble impurities settle as anode mud.
Corrosion and alloys
Rusting of iron needs both oxygen (air) and water (moisture); in boiled water with oil on top, or in dry air with a drying agent, the nail does not rust. Rust is hydrated iron(III) oxide, Fe₂O₃·xH₂O. Silver tarnishes black (silver sulphide) and copper turns green (basic copper carbonate). Prevention puts a barrier between metal and air: painting, oiling and greasing, galvanisation (a coat of zinc), chrome plating and anodising (a thick oxide layer on aluminium). Alloying also helps.
An alloy is a homogeneous mixture of a metal with other metals or non-metals. Alloys are usually harder and more corrosion resistant, with a lower melting point and lower electrical conductivity than the pure metal. Pure iron is soft; adding about 0.05 % carbon makes it hard and strong, which is why railway rails and bridges use steel.
| Alloy | Made of | Note |
|---|---|---|
| Steel | Iron and carbon | Rails, bridges, tools |
| Stainless steel | Iron, nickel, chromium, carbon | Does not rust |
| Brass | Copper and zinc | Fittings, utensils |
| Bronze | Copper and tin | Bells, statues |
| Solder | Lead and tin | Low melting point, used to join wires |
| Amalgam | Mercury with another metal | Any alloy that contains mercury |
Carbon and its compounds
Carbon (atomic number 6, configuration 2, 4) has four valence electrons. To form an ion it would have to lose or gain four electrons, which is energetically hard, so it shares electrons and forms covalent bonds. Carbon is tetravalent and shows catenation, the ability to link with itself in long chains, branches and rings. Covalent compounds have weak forces between molecules, so they have low melting and boiling points and are poor conductors of electricity.
| Form | Structure | Properties |
|---|---|---|
| Diamond | Each C bonded to four others in a rigid 3-D lattice | Hardest natural substance; does not conduct |
| Graphite | Each C bonded to three others in hexagonal layers | Soft, slippery, conducts electricity; lubricant |
| Fullerene (C-60) | Football-shaped cage of 60 carbon atoms | Named after Buckminster Fuller |
Hydrocarbons are compounds of carbon and hydrogen. Saturated ones (alkanes, general formula CₙH₂ₙ₊₂) have single bonds only; unsaturated ones have a double bond (alkenes, CₙH₂ₙ) or a triple bond (alkynes, CₙH₂ₙ₋₂). A homologous series is a family with the same functional group and similar chemistry, in which successive members differ by CH₂ (14 u). Name stems: meth 1, eth 2, prop 3, but 4, pent 5, hex 6 carbons. Natural gas and CNG are mainly methane.
| Carbons | Alkane | Alkene | Alkyne |
|---|---|---|---|
| 1 | CH₄ methane | — | — |
| 2 | C₂H₆ ethane | C₂H₄ ethene | C₂H₂ ethyne |
| 3 | C₃H₈ propane | C₃H₆ propene | C₃H₄ propyne |
| 4 | C₄H₁₀ butane | C₄H₈ butene | C₄H₆ butyne |
| 5 | C₅H₁₂ pentane | C₅H₁₀ pentene | C₅H₈ pentyne |
Counting bonds: the number of covalent bonds in an alkane CₙH₂ₙ₊₂ is 3n + 1. Methane has 4, ethane has 7 (six C–H and one C–C) and propane has 10 (eight C–H and two C–C). Functional groups: –OH alcohol, –CHO aldehyde, >C=O ketone, –COOH carboxylic acid. Saturated hydrocarbons burn with a clean blue flame; unsaturated ones burn with a yellow, sooty flame when air is limited. Addition of hydrogen to unsaturated oils with a nickel catalyst gives saturated fats (hydrogenation, as in vanaspati ghee).
Ethanol, ethanoic acid, soaps and detergents
Ethanol (C₂H₅OH) is a neutral liquid. It reacts with sodium to release hydrogen, 2Na + 2C₂H₅OH → 2C₂H₅ONa + H₂, and on heating with concentrated H₂SO₄ at 443 K it loses water to give ethene. It is oxidised to ethanoic acid by alkaline potassium permanganate or acidified potassium dichromate. It is used in medicines, tinctures and cough syrups. Industrial ethanol is made unfit to drink (denatured) by adding poisonous substances such as methanol or pyridine, and a dye. Ethanoic acid (CH₃COOH) is a weak acid: it freezes at about 290 K (so pure ‘glacial’ acid solidifies in winter) and a 5 to 8 % solution in water is vinegar. It releases CO₂ from carbonates, 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂.
Esterification: an acid and an alcohol react in the presence of concentrated H₂SO₄ to form an ester, which has a sweet, fruity smell and is used in perfumes and flavouring: CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ + H₂O. Saponification is the reverse in alkali: ester + NaOH → alcohol + sodium salt of the acid, and with fats and oils it is the way soap is made.
Soaps are sodium or potassium salts of long-chain carboxylic acids. A soap ion has an ionic head that is water-loving and a hydrocarbon tail that is oil-loving. In water, soap molecules form a spherical micelle with the tails pointing inward around the oil or grease and the heads facing outward, so the dirt is pulled into the water and rinsed away. In hard water, which contains calcium and magnesium salts, soap forms an insoluble scum. Detergents (generally sodium salts of sulphonic acids, or ammonium salts) do not form scum in hard water, but many are not biodegradable, whereas soaps are.
Key takeaways
- Metals are malleable, ductile and conduct well; exceptions: Hg is liquid, Na and K are soft, graphite conducts, diamond is hardest. Al₂O₃ and ZnO are amphoteric.
- Reactivity: K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Hg, Ag, Au. A metal displaces only those below it; those above H release hydrogen from dilute acid.
- Extraction: top five by electrolysis, middle metals by roasting or calcination then carbon reduction, bottom metals by heating. The thermit reaction welds rails.
- Rusting needs air and water. Prevent it by paint, oil, galvanising (zinc), chrome plating or alloys: steel is iron with carbon, brass copper with zinc, bronze copper with tin, solder lead with tin.
- Carbon is tetravalent and shares electrons: covalent compounds have low melting points and do not conduct. Alkanes CₙH₂ₙ₊₂, alkenes CₙH₂ₙ, alkynes CₙH₂ₙ₋₂; a homologous series differs by CH₂.
- Ethanol plus sodium gives hydrogen; ethanoic acid (vinegar 5 to 8 %) releases CO₂ from carbonates; acid plus alcohol gives a sweet-smelling ester. Soap micelles hold grease in the tail; soap forms scum in hard water, detergent does not.
Practice questions (18)
Attempt each one before opening the answer. Every explanation names the tempting wrong option as well as the right one, because that is where marks are lost.
Which metal is a liquid at room temperature?
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Answer: C — Mercury
Mercury is the only common metal that is liquid at room temperature. Bromine is also a liquid at room temperature but it is a non-metal, which is why it is the tempting distractor.Which of these metals is placed highest in the reactivity series?
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Answer: D — Calcium
The order is K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Hg, Ag, Au, so calcium is highest among the four. Magnesium comes next, then aluminium and zinc.In which of these combinations will a displacement reaction NOT occur?
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Answer: D — Copper metal in zinc sulphate solution
Copper lies below zinc in the series, so it cannot displace zinc from its salt. In the other three the added metal (Zn, Fe, Mg) is above the metal in solution, so each displaces it.Arrange magnesium, zinc, copper and iron in decreasing order of reactivity.
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Answer: A — Mg > Zn > Fe > Cu
From the series: Mg, Zn, Fe, then Cu. The most common error is to place iron above zinc, which reverses their positions.Which metal is extracted by electrolysis of its molten chloride or oxide?
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Answer: B — Sodium
Sodium sits at the top of the series, so carbon cannot reduce its compounds and electrolysis of molten NaCl is used. Zinc is obtained by carbon reduction, and mercury and copper by heating the sulphide.About the thermit reaction Fe₂O₃ + 2Al → 2Fe + Al₂O₃: P: it is a displacement reaction. Q: aluminium acts as the reducing agent. R: it absorbs heat from the surroundings. S: the molten iron is used to weld railway tracks. Which are correct?
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Answer: A — P, Q and S only
Aluminium, being more reactive, displaces iron and reduces Fe₂O₃, and the enormous heat released melts the iron for welding rails. R is wrong because the reaction is strongly exothermic, not endothermic.Iron nails rust fastest under which condition?
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Answer: C — Moist air, in contact with water
Rusting needs both oxygen and water. Only the moist-air condition supplies both; boiled water with oil lacks dissolved oxygen, and the other two lack water or oxygen.Why does a galvanised iron sheet remain protected even where its zinc coat is scratched?
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Answer: B — Zinc is more reactive than iron, so it is attacked first
Zinc is above iron in the reactivity series, so it corrodes in preference to iron and protects it. The statement that zinc is less reactive reverses the series.Which pair correctly gives an alloy and its constituents?
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Answer: B — Brass: copper and zinc
Brass is copper with zinc. Bronze is copper with tin, solder is lead with tin, and steel is iron with carbon, so those pairs are mismatched.Magnesium (atomic number 12) combines with chlorine (atomic number 17). How many chloride ions combine with each magnesium ion in the compound formed?
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Answer: B — 2
Mg has configuration 2, 8, 2 and loses two electrons to form Mg²⁺; each Cl (2, 8, 7) gains one electron, so two Cl⁻ are needed and the formula is MgCl₂.Which allotrope of carbon conducts electricity?
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Answer: B — Graphite
In graphite each carbon uses three of its four valence electrons in bonding, and the free electrons in the layers conduct. In diamond all four are used, so it is an insulator.How many covalent bonds are present in one molecule of propane, C₃H₈?
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Answer: C — 10
Propane has eight C–H bonds and two C–C bonds, a total of 10, which agrees with the formula 3n + 1 for n = 3. Counting only the C–H bonds gives 8.A hydrocarbon in the same homologous series as ethene contains 5 carbon atoms. What is its molecular formula?
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Answer: D — C₅H₁₀
The alkene series has the general formula CₙH₂ₙ, so five carbons give C₅H₁₀. C₅H₁₂ is pentane, the alkane, and C₅H₈ belongs to the alkyne series.Which functional group is present in ethanoic acid?
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Answer: C — –COOH
Ethanoic acid is a carboxylic acid, so it carries the –COOH group. The –OH group alone belongs to alcohols such as ethanol, and –CHO to aldehydes.For ethanol and ethanoic acid, P: ethanol reacts with sodium to release hydrogen. Q: ethanoic acid releases CO₂ from sodium carbonate. R: ethanoic acid is a strong acid like HCl. S: acid and alcohol on warming with concentrated H₂SO₄ give an ester. Which are correct?
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Answer: A — P, Q and S only
P, Q and S are standard reactions. R is false: ethanoic acid is only a weak acid that ionises partly in water, so statements that include R are wrong.In a soap micelle formed around a drop of grease, which part of the soap molecule is buried in the grease?
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Answer: A — The hydrocarbon tail, which is oil-loving
The hydrocarbon tail is hydrophobic and oil-loving, so it points into the grease; the ionic head is water-loving and faces outward. Swapping them is the standard error.Why does a detergent work well in hard water, where soap forms a curdy scum?
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Answer: B — Its calcium and magnesium salts remain soluble in water
Soap forms insoluble calcium and magnesium salts, the scum. The corresponding detergent salts stay dissolved, so no scum forms. The claim that the salts are insoluble describes soap, not detergent.An unsaturated hydrocarbon burning in a limited supply of air usually burns with which kind of flame?
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Answer: B — A yellow flame that gives soot
Unsaturated hydrocarbons burn incompletely in limited air, producing a yellow sooty flame. Saturated hydrocarbons in good air supply give the clean blue flame.