Metals (Part 1) Learning Objectives ns She general physical properties of metals as solids having high metting and boiling points, cesteanie. good conductors of heat and electricity in terms of inate ae coal a ith another element, ; desoribe alloys as a mixture of a metal wit identity representations of metals and alloys from diagrams of UCU ts explain why alloys have different physical properties to their constitu Reactivity of metals a place in order of reactivity calcium, copper, (hydrogen), iron, lead, magnesium, potassit sodium and zine by reference to : (i) the reactions, if any, of the metals with water, steam, dilute hydrochloric acid (“and oxygen) i) the reduction, if any, of their oxides by carbon and/or by hydrogen 1 Gesenbe the reactivity sees as related to the tendency of a metal to form its positive ion, illustrated by its reaction with (i) the aqueous ions of the other listed metals (ii) the oxides of the other listed metals ‘+ deduce the order of reactivity from a given set of experimental results describe the action of heat on the carbonates of the listed metals and relate thermal stability to the reactivity series ‘+ explain unreactivity of aluminium * discuss the displacement reaction taking place in Thermit Reaction (aluminium and oxides of iron) and relate to exothermic reaction and its use in railway tracks Extraction of metals * describe the ease of obtaining metals from their ores by relating the elements to their positions in the reactivity series + explain how reactivity of metals determines the methods of extraction * extraction of metal from its oxides (up tll ‘ron’ with hydrogen and ‘zinc’ with carbon) Iron * describe and explain the essential reactions in the extraction of iron using haematite, limestone and coke in the blast furnace * describe steets as alloys which are a mixture of iron with carbon or other metals and how controlled use of these additives changes the properties of the iron, e.g. high carbon steels are strong but brittle whereas low carbon steels are softer and more easily shaped * state the uses of mild steel, e.g. car bodies; machinery, and stainless steel, e.g. chemical plants: cutlery; surgical instruments * describe the essential conditions for the corrosion (rusting) of iron as the presence of oxygen and water: prevention of rusting can be achieved by placing a barrier around the metal, e.g. painting; greasing; plastic coating; galvanising * describe the sacrificial protection of iron by a more reactive metal in terms of the reactivity series where the more reactive metal corrodes preferentially, e.g. underwater pipes have a piece of Magnesium attached to them Recycling of metals J Gescribe metal ores as a finite resource and hence the need to recycle metals, e.g. recycling of iron 5 je iScuUSS the social, economic and environmental issues of recycling metals Viecus metal recycling industry in Singapore (e.g. Eco-Recycling Park at Tuas) and other parts of the ‘orld; “discuss how Singapore promotes 3 R's; “propose plans and programs that can support recycling of metals Chemistry/ Metals BL4.4 * A metallic bond is the METALS Metal ions are closely packed together in a regular 3-dimensional pattern or laticg valence electrons from each atom free to move at random in the space between the m, forming a ‘sea’ of valence electrons. free-moving valence electrons. Metals are elements which lose electrons to form positive ions (except hydrogen), with th Metal ong electrostatic force of attraction between positive metal ions and ‘sea’ o¢ 1.2 DIFFERENCES IN PROPERTIES BETWEEN METALS & NON-METALS (A) PHYSICAL PROPERTIES Physical Metals Non-metals Properties Examples | Copper, sodium, gold Hydrogen, carbon, oxygen ‘Appearance | Are usually shiny (lustrous) and can be | Are usually dull and cannot be polished polished Melting and | Most are solids at room temperature with | Are usually liquids or gases at room Boiling high melting and boiling points temperature with low melting and boiling points points (exception: mercury with melting point of -39°C, Group 1 metals, etc.) (exception: diamond, silicon and graphite have high melting points due to their giant molecular structures) | Heat and | Are good conductors of heat and electricity | Are poor conductors of heat and electricily Electrical (exception: graphite) | Conductivity ] Density | Have relatively high densities Have relatively low densities | Malleabilty Malleable - can be bent and beaten into | Brittle (breaks without bending and different shapes stretching) | Ductiity | Ductile ~ can be stretched and pulled into | Not ductile wireswhy are metals ductile and malleable? © Atoms in Atoms in atoms to pure metals are packed in layers in an order pure metal are of the same size. This slide over each other easily when a fore and malleable. KEK SEE N [Force Why do metals have high melting and boiling points? ly manner. lows the orderly layers of the same sized is applied. Hence, pure metals are ductile «Atoms ina metal are packed tightly in layers and are held together by strong metallic bonds. + Large amount of energy is needed to overcome the strong electrostatic forces of attraction between positive metal ions and the ‘sea’ of free-moving valence electrons. Why do metals conduct electricity? «Presence of ‘sea’ of free-moving valence electrons helps to conduct electricity. (B) CHEMICAL PROPERTIES Chemical Properties Metals Non-metals | | Formation of ions Form positive ions by losing electrons. Na > Nat + & Mg > Mg* + 2e Eg Metals are good reducing agents. Form negative ions by gaining | electrons. | Eg. Ch + 2e + 2cr | OQ, + 4e — 20% | Formation of oxides Form basi oxides or amphoteric oxides by burning / reacting with oxygen. E.g. 4Na(s) + O2(9) > 2Naz0(s) 2Zn(s) + O2(g) > 2ZnO(s) Form acidic oxides or neutral oxides by burning / reacting with oxygen. Eg. — S(s) + O29) > SOA) 2Ha(g) + O2(g) >» 2H20(! Soluble basic oxides dissolve in water to form alkalis E.g. NaO(s) +H:0() > 2NaOH(aq) Soluble acidic oxides dissolve in water to form Eg $0.(g) + H20(!) -» H2SOs(aa) | 832.1 ALLoys Pure metals are not commonly used a! reacting with oxygen and water harder and stron. + Most metals are used inthe form of alloys because hey 98 EE a ane nan ‘+ Some alloys have special properties not found 7 FOsion, J they are soft and many of them may corrode g, ly, Pte me tals? Why are alloys stronger and harder than pure me! “This ig because in alloys, atoms of added element have a sifferent size fom atoms inthe, + This i . metal / ‘+ This disrupts the orderly arrangement of 2 ‘+ Hence, itis much harder for the atoms tos soms in pure metals. lide over each other when a force is applied. Structure of an alloy atom of other element main metal atom 2.2 COMMON ALLOYS Alloy Composition Property Uses Wild steel Fon, carbon Tard and stiong ar bodies, machinery, buildings, ships ‘Stainless steel | iron(73%) ‘strong and resistant to corrosion | cutlery, hospital and cheer) ‘chemical equipment, pipes a | sarong chemical industries a copper, tn Fard and strong medals, words, statues Br = =, connenTOR) ‘does not corrode easily, decorative omaments, ine(30%) yellow colour like gold musical instruments, pins ot | power plug | Solder Tin{6O%) Tow . lead( 50%) ‘melting point Joining metals | Brann — Tara | luminium, copper, | ight felon ight, strong and durable aircraft parts manganese Cupronickel [omper niks —F | siNery a po | "Y appearance, unreactive coins eee | | Chemistry/ Metals4 REACTIVITY SERIES OF METALS Metals can be listed in order of their chemical reactivity as given below. | The Reactivity Series of Metals Potassium Most Reactive Sodium Calcium Magnesium Aluminium (Carbon) Zine Iron Tin Lead (Hydrogen) Copper Silver Gold Least Reactive A metal ‘high up’ in the reactivity series: + reacts vigorously and quickly with chemicals; * corrodes easily; + readily gives up electrons in reactions to form positive ions. A metal ‘low down’ in the reactivity series: ‘+ does not react vigorously with chemicals; ‘+ does not corrode easily; + does not readily give up electrons in reactions to form positive ions. Note: * A metal higher up in the reactivity series has a greater tendency to lose electrons to form bositive ions than a metal lower down in the reactivity series. * Hydrogen is not a metal. It is placed in the reactivity series as a reference — metals below hydrogen in the series do not react with acids to produce hydrogen gas.3.2 REACTION OF METALS WITH COLD WATE ROR STEAM REACTION OF METALS WITH COLD WATER OR STEAM Ch | Metal] Reaction with cold water or s Reaction with cold wi aie _ twit att aan - Potassium + Reacts very violently in cold water 2K(s) + 2H.010-> 2x0, lg) (Group 1) | 6 Highly exothermic - 4 Koa) + Potassium hydroxide_solution 2” Botany hydrogen gas produced : «Potassium darts rapidly on the surface 0 4 water and melts. | * Eizzing occurs «The hydrogen ignites instantly. The metal sa soon ig also set on fire, with sparks and a lilac) oye) flame ; Sodium |* Reacts violently in cold water 2Na(s)*2H,0()-+2Na0He@e gt (Group 1) | 6 Sodium hydroxide solution and hydrogen Kaa}+ Hla) gas produced sodium «| Sodium darts rapidly on the surface of water and melts into silvery ball © Fizzing occurs © Sodium may catch fire and burn with yellow flame alkali soliton Note: If indicator is added: NaOH(eq) * green universal indicator turns violet | © red litmus turns blue Calcium [+ Reacts readily with cold water goon} |.” Fpld efarvancanca wean, exlouriows and | “Ait? * SHOUL-+CmioHhdactetha odourless gas evolved + Calcium hydroxide solution and hydrogen gas hydrogen gas produced * Colourless solution soon turns cloudy as calcium hydroxide is only slightly soluble calcium inwater Magnesium [~ Re 4, acts very slowly wit = (Group 2) afew — with cold water with | Mg(s) + Hz0(g) > MgO(s) + HAs) © Hot \ydrogen gas produced | glass magnesium reacts violently with | Wool steam soaked jrotal nyrogens * Magnesium oxide in, water produced and hydrogen gas | * Silvery/grey may | nesi and bright ee cone Solid turns white fl | the reaction © Produced during dt | Chemistry/ Metals 86_— qatar] Reston (Group 13) Fxtamintum _———chemicalEquation —| = Aluminium metal does n°! with water or steam “This is because aluminium is covered with nin layer of non-porous_aluminium ‘oxide which adheres strongly to tne metal ‘and protects it from reacting Chemical Equat with state S$: ymbols) “Formation of non-porous protective layer of AlzOs: AAl(s) + 302g) > 2A203(5) Protective non- porous coat of aluminium oxide Zine «Grey zinc solid slowly becomes coated ~ Does not react with cold water + Hot zinc reacts readily with steam + Zinc oxide and hydrogen gas produced with a yellow solid which becomes white when cold Zns) + H20(g) -» Zn0(s) + Ha9) Tron ~ Does not react with cold water + Red hot iron reacts slowly with steam © Iron({IL.IM) oxide (FesO.) and hydrogen «Grey iron solid tums red hot on heating gas formed and black when cooled 3Fe(s) + 4H20(g) > Fes0.(s) + 4H2(g) Lead Copper Silver Gold No reaction with cold water or steam Phamictnil haatale3-3. REACTION OF METALS WITH DILUTE / . series do not react with acids to Metals below hydrogen in the reactivity serios done! icacl i 8 0 Produce gag, * Metals above hydrogen in the reactivity series can displace rom diate agen Reactive metal + Acid —* Salt + Hydrogen al] Reaction with dilute hydrochloric acid Chemical Equay [ Metat Reaction with dil id Chemin = Potassium [> Reacts explosively | PRC) # BHCHaR) > akCHaas (Group 1) (Should NOT be carried out in schoo! ae ) Sodium laboratory) * PHCKad)-> 2Nacagy+ ig (Group 1) ) Calcium | Reacts violently Cals) + 2HClaq) > CaCifaq + ual | | (Group2) |+ Very rapid effervescence seen, \ colourless and odourless gas evolved | * Colourless calcium chloride solution and hydrogen are formed Magnesium |+ Reacts rapidly Mg{(s) + 2HCi(aq) > MgCix(aq) + Hig) (Group 2) | Rapid effervescence seen, colourless and odouriess gas evolved * Colourless magnesium chloride solution and hydrogen are formed ‘Aluminium | Aluminium does not seem to react at | A/2O3(s) + 6HC/(aq) > 2A/Ch(aq)+ (Group 13) first as itis covered by a layer of non- | protective 3H,0(I) porous aluminium oxide which | oxide layer adheres strongly to the metal Y Spatium | 2AM(S)* BHC/(aq)-> 2A/Cis(aq)+ 3H) Jy) LA, (Al underneath exposed once AlOs layer is reacted away) + However, hydrochloric acid will react with aluminium oxide to form soluble aluminium chloride and water * Once the oxide layer is reacted away, |, the reaction between the aluminium ' and acid is rapid reactive pid as the metal is | Zinc "> Reacts moderately aw ———— + Rescis moderately fast [21+ Brera) > enc Mi * Steady effeveste tie a cies nae 7 | nd odourless gas evolved | 1 chlori hydrogen are formed ide solution and eee | | | Chemistry/ Metals 88Metal iron | * — ‘Lead |e (Group 14) eacts slowly ‘Slow effervescence seen, and odourless gas evolved Pale green iron(Il chloride solution ‘and hydrogen are formed colourless: ‘drochioric acid | Chemical Equation ____(with state symbols) Fe(s) + 2HCaq) > FeCis(aa) + Ha(9) ction stops Reacts very slowly and rea before completion Insoluble lead(!!) chloride salt formed ‘will coat onto surface of the lead metal and prevent further reaction between the acid and lead metal Pb(s) + 2HCi(aq) > PbCla(s) + HA(g) No reaction with dilute hydrochloric acid 1. Most metals do react with dilute nitric acid but the products formed depend on the concentration of the acid and the nature of hydrogen gas. Eg. the metals, Oxides of nitrogen (NO, NOz) may be formed instead of Zn(s) + 4HNOs(aq) > Zn(NOs)2(aq) + 2NO2(g) + 2Hz20() 2. Dilute nitric acid can oxidise unreactive metals such as copper. Eg. 3Cu(s) + 8HNOs(aq) > 3Cu(NOs)2(aq) + 2NO(g) + 4H20(/)Summary 1. Reaction of Metal with Water/Steam Reactive metal + cold water -> metal hydroxide solution (alkali) + hydrogen (K, Na, Ca) Note: Magnesium does react with cold water but very Slowly. _ TT Heated moderately reactive metal + steam > metal oxide (Mg, Zn, Fe) Unreactive metals (Pb, Cu, Ag, Au) will NOT react with cold water or steam 7 2. Reaction of Metal with Dilute Hydrochloric Acid Metal + Dilute hydrochloric acid > metal chloride + hydrogen gas | (above hydrogen in the reactivity series) | Quick Check: The table shows the results of adding metals, P, Q and R to dilute hydrochloric acid and to water. Metal Dilute hydrochloric acid Water P Hydrogen produced Hydrogen produced Q Hydrogen produced No Reaction. R No reaction No reaction Rank the above metals from the most reactive to the least reactive. The following shows a list of metals in order of their reactivity series. Most Reactive ———__+ Least Reactive Calcium Magnesium Zinc Iron Lead Copper (2) Which of the metals will react most quickly with cold water? Equation: ee (b) Na i ? Name the metal which will react with steam but only react slowly with cold water (©) Name the gas py identity this gas Gasis Test eee eet | | 0 , ‘iveed during the reaction in (a) and (b). Describe how you would test and aAPLACEMENT OF METALS FROM METAL SALT SOLUTIONS 44 ‘A more reactive metal will displace the less reactive metal from its salt solution. ‘A more reactive metal loses electrons more. readily to form positive ions. long of the less reactive metal accept the electrons from the more reactive metal to form the metal atoms. «Hence, a more reactive metal will displace «The further apart the two metals in the reactivity series, reaction. «Such displacement reaction is often accompanied by = change in appearance(colour) of metal, change in colour of salt solution, ~ heat change (heat evolved). the less reactive metal from its salt solution. the easier/faster the displacement Example: Experiment: An iron nail is placed in copper(II) sulfate solution. —test (— test tube tube ion > |__ reddish brown copper | |ron Solid on iron nal {blue LL pate oreen copper(ll) iron() sulfate sulfate solution solution Equation: Fe(s) + CuSO.(aq) > Cu(s) + FeSO,(aq) Observations: (1) The iron nail is coated with a reddish brown solid. (2) The blue copper(II) sulfate solution turns pale green after some time. Explanation: * Iron, being more reactive than copper, loses electrons more readily than copper. + Iron displaces copper from blue copper(II) sulfate solution. Reddish brown copper solid and pale een iron(II) sulfate solution are formed. lonic Equation: Fe(s) + Cu’*(aq) -> Fe**(aq) + Culs) Half Equations: Fe — Fe + 2e oxidised Cut + 2e" > Cu reduced Qn: Explain why this is a redox reaction in terms of electrons transfer. Fe is oxidised as Fe loses electrons to form Fe**. CuSO, is reduced as Cu** gains electrons to form Cu.