Chapter 19Metals and Their Reactivity LEARNING OUTCOMES Describe the physical and chemical properties of metals; Explain why metal alloys are often used in place of metals; Discuss the reactivity of metals, and deduce the order of reactivity of metals based on experimental results of data supplied Describe the reactions of metallic hydroxides, nitrates and carbonates
Chapter 19Metals and Their ReactivityPhysical Properties of metals Metals are usually hard and shiny. They are malleable (can be bent or hammered into sheets) and ductile (can be stretched or drawn into wires). Pure metals are weak because their atoms can slide over each other easily when a force is applied.
Chapter 19Metals and Their ReactivityPhysical Properties of metals Metals are good conductors of heat and electricity. Metals have high density. They have high melting points and boiling points. E.g. iron has a melting point of 1538 oC and tungsten has a melting point of 3422 oC.
Chapter 19Metals and Their ReactivityChemical Properties of metals Metals lose electrons to form positively charged ions (electropositive). Cu Cu2+ + 2e− Most metals react with acids to produce hydrogen gas. Mg(s) + H2SO4(aq) MgSO4(aq) + H2(g) Metals form basic oxides when they react with oxygen. 2Ca(s) + O2(g) 2CaO(s) Most metals react with water to produce metallic hydroxides and hydrogen gas. 2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g)
Chapter 19Metals and Their ReactivityStructure of metals The atoms of metals are packed very closely together in neat layers. Pure metals are weak because the layers of atoms can slide over one another when a force is applied.
Chapter 19Metals and Their ReactivityAlloys of metals A mixture of a metal with another metal (or non-metal) is called an alloy. Brass Brass is an alloy of copper and zinc; bronze is an alloy of copper and tin. Bronze Stainless steel is an alloy of iron and small amounts of carbon, Stainless steel chromium and nickel.
Chapter 19Metals and Their ReactivityStructure of alloys In alloys, the atoms of different metals or elements are of different sizes. This disrupts the orderly layers of atoms and makes it harder for the layers of atoms to slide over one another when a force is applied. This explains why alloys are harder and stronger than the pure metals.
Chapter 19Metals and Their Reactivity Quick Check 11. State 2 physical properties of metals which make them useful as constructing materials.2. What is meant by the terms: “ malleable” and “ ductile ” ?3. What is an “ alloy” ? Give two examples of alloys.4. Explain why alloys are harder and stronger than the pure metals.5. Explain why brass is used for making the pins of the power plug, instead of pure copper. Solution
Chapter 19Metals and Their ReactivitySolution to Quick check 11. (a) Metals are strong and malleable. (b) They can withstand high temperatures.2. Malleable means it can be hammered into sheets without breaking; Ductile means it can be stretched into wires without breaking.3. An alloy is a mixture of a metal with another element. Brass and steel are examples of alloys.4. Unlike pure metals, the atoms in an alloy are of different sizes. This makes it more difficult for the atoms to slide over each other when a force is applied.5. Brass is harder and stronger than pure copper. Return
Chapter 19Metals and Their ReactivityThe Reactivity Series The Reactivity Series Potassium (K) Most reactive shows the order of Sodium (Na) reactivity of metals in Calcium (Ca) their reactions with Magnesium (Mg) water, steam, and Aluminium (Al) dilute acids. Zinc (Zn) Iron (Fe) Lead (Pb) Copper (Cu) Silver (Ag) Least reactive
Chapter 19Metals and Their ReactivityHow to remember the Reactivity Series Potassium (K) Katty’s Most reactive Sodium (Na) Naughty Calcium (Ca) Cat Magnesium (Mg) Mingled with Aluminium (Al) Alice and Zinc (Zn) Zarina; Iron (Fe) Fearlessly Lead (Pb) Plundering her Copper (Cu) Cupboard of Silver (Ag) Silver Least reactive
Chapter 19Metals and Their ReactivityThe Reactivity SeriesMost Reactive Potassium React with cold Explode with Sodium water steam and Calcium dilute acids ……………...... Magnesium React with Aluminium React dilute acids Zinc with with Iron steam decreasing Lead vigour ……………….. Do not react Copper with water, Silver steam or dilute Least Reactive acids
Chapter 19Metals and Their ReactivityReaction of potassium with water The first three metals: potassium, sodium and calcium reactvery vigorously with cold water to produce hydrogen gas and analkali. When a small piece of potassium is placed into a trough ofwater, it immediately bursts into flames, and moves rapidly onthe water surface. The hydrogen gas given off makes it burnexplosively. An alkali, potassium hydroxide, is also formed. 2K(s) + 2H2O(l) 2KOH(aq) + H2(g)
Chapter 19Metals and Their ReactivityReaction of sodium with water Sodium reacts less vigorously than potassium with cold water. When a small piece of sodium is placed into atrough of water, it melts into a silvery ball anddarts about on the water surface. It mayoccasionally burst into flame. An alkali, sodiumhydroxide, is left in the solution. 2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g)
Chapter 19Metals and Their ReactivityReaction of calcium with water When a small piece of calcium is placed in abeaker of water, it sinks to the bottom of the water.It reacts vigorously with the water, producingbubbles of hydrogen. The water turns slightly milky due to theformation of calcium hydroxide, which is notvery soluble in water. pop Ca(s) + 2H2O(l) Ca(OH)2 (aq) + H2 (g) The hydrogen can be collected in a test tube and tested with a lighted splint.
Chapter 19Metals and Their ReactivityReactions with steam Magnesium, zinc and iron do not react with cold water but react with steam when heated to produce hydrogen and a metal oxide: Equations: Mg(s) + H2O(g) MgO(s) + H2(g) Zn(s) + H2O(g) ZnO(s) + H2(g) 3Fe(s) + 4H2O(g) Fe3O4(s) + 4H2(g)
Chapter 19Metals and Their ReactivityReaction of magnesium with steam An experiment is set up as shown in the diagram. When the test tube is heated, steam is produced which reacts with the hot magnesium ribbon. The magnesium reacts with the steam, producing hydrogen gas which burns at the jet of the glass tube. Mg + H2O MgO + H2
Chapter 19Metals and Their ReactivityReactions with dilute acids Potassium (K) Sodium (Na) All metals from lead and above Calcium (Ca) react with dilute acids to form a …………………… salt and hydrogen. Magnesium (Mg) React with The higher the metal is in the dilute acids Aluminium (Al) reactivity series, the more Zinc ( Zn) vigorous the reaction. Iron (Fe) Potassium, sodium and Lead (Pb) …………………… calcium will explode with No reaction Copper (Cu) acids, while lead will only react with dilute Silver (Ag) very slowly when heated. acids
Chapter 19Metals and Their ReactivityReactions of metals with dilute hydrochloric acid The picture shows that magnesium reacts very vigorously withdilute hydrochloric acid, followed by zinc.Lead has almost no reaction with dilute hydrochloric acid. Copper does not react with dilute hydrochloric acid.
Chapter 19Metals and Their ReactivityNon-reactivity of Aluminium Potassium (K) Aluminium which is Sodium (Na) relatively high in the Calcium (Ca) Reactivity Series seems to …………………… have no reaction with water, Magnesium (Mg) steam and dilute acids. Aluminium (Al) Zinc ( Zn)This is because aluminium is Iron (Fe)coated with a thin layer of aluminium …………………oxide that is invisible to the naked Lead (Pb)eye. This layer protects the metal Copper (Cu)from contact with the reagents. Silver (Ag)
Chapter 19Metals and Their ReactivityQuick Check 21. Which metal is (a) the most reactive, (b) the least reactive, in the reactivity series? (Exclude silver)2. Arrange the following metals from the most reactive to the least reactive: calcium, zinc, magnesium, sodium, copper and aluminium.3. What gas is given out when metals react with water and dilute acids ?4. Write a balanced chemical equation for the following reactions: (i) sodium and water, (ii) magnesium with steam, (iii) zinc with dilute hydrochloric acid.5. When a piece of aluminium was placed in a test tube containing dilute hydrochloric acid, there was no reaction. When the aluminium was rubbed with some sodium hydroxide solution and then re-immersed in the hydrochloric acid, the aluminium reacted vigorously with the acid. Explain why this happens. Solution
Chapter 19Metals and Their ReactivitySolution to Quick check 21. (a) Potassium, (b) copper2. Sodium, calcium, magnesium, aluminium, zinc, copper3. Hydrogen gas4. (i) 2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g) (ii) Mg(s) + H2O(l) MgO(s) + H2(g) (iii) Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)5. The piece of aluminium was coated with a layer of aluminium oxide which protects it from the hydrochloric acid. Rubbing it with sodium hydroxide removed the layer of aluminium oxide, and hence the aluminium was able to react with the hydrochloric acid. Return
Chapter 19Metals and Their ReactivityThe Reactivity series and ease of forming ions The reactivity series is related to the ease of the metals in forming positive ions by losing electrons. The more easily a metal loses its outermost electron(s), the more reactive it will be. A more reactive metal will form a more stable compound with a non-metal. Hence It is more difficult for oxides and carbonates of the more reactive metals to be reduced or decomposed by heat.
Reduction of metal oxides Potassium Sodium Calcium Not reduced by carbon Magnesium Not reduced Aluminium by hydrogen (Carbon) Zinc Iron Lead Reduced by (Hydrogen) carbon Reduced by Copper hydrogen Silver
Chapter 19Metals and Their ReactivityReduction of metal oxides by carbon Oxides of metals which are below carbon in the reactivity series are reduced to the metal when heated with carbon. This process is used in the industry to obtain the metals from their ores. Examples: ZnO(s) + C(s) Zn(s) + CO(g) CuO(s) + C(s) Cu(s) + CO(g)
Chapter 19Metals and Their ReactivityReduction of metal oxides by hydrogen Oxides of metals which are below hydrogen in the reactivity series are reduced to the metal when heated with hydrogen. Examples: CuO(s) + H2(g) Cu(s) + H2O (g) AgO(s) + H2(g) Ag(s) + H2O(g)
Chapter 19Metals and Their ReactivityDisplacement Reactions Zinc metal When a piece of zinc is placed in copper(II) sulphate solution, a brown layer of copper is formed on the surface of the zinc.Zn + CuSO4 ZnSO4 + Cu CopperThe zinc has displaced the copper from the coatingcopper(II) sulphate solution because zinc ismore reactive than copper. Copper(II) In general, a more reactive metal will displace a less sulphatereactive metal from their salts in solution. solution
Chapter 19Metals and Their ReactivityDisplacement Reactions Zinc metal If a piece of zinc is placed in magnesium sulphate solution, no reaction will take place. This is because zinc is less reactive than magnesium No reaction (lower in the reactivity series than magnesium) and hence cannot displace magnesium ions from its magnesium sulphate solution. solution
Chapter 19Metals and Their ReactivityDisplacement of metal from their oxides A more reactive metal can displace a less reactive metal Potassium (K) Most reactive from its oxide when they are heated together. Sodium (Na) Calcium (Ca) E.g. 2Al + Fe2O3 Al2O3 + 2Fe Magnesium (Mg) This reaction is used in Aluminium (Al) the production of Zinc ( Zn) “thermite”, which uses Iron (Fe) the molten iron formed Lead (Pb) to repair cracks on Copper (Cu) railway lines. Silver (Ag) Least reactive
Chapter 19Metals and Their ReactivityAction of heat on metal carbonates Carbonates decompose when heated to produce Potassium (K) Carbonates not decomposed by the metal oxides and heat carbon dioxide. Sodium (Na) E.g. CaCO3 CaO + CO2 More difficult Calcium (Ca) However, the more Magnesium (Mg) Carbonates reactive the metals Aluminium (Al) decomposed by heat are, the more Zinc ( Zn) difficult it is for their Iron (Fe) carbonates to Lead (Pb)decompose. Copper (Cu) Easier Silver (Ag)
Chapter 19Metals and Their ReactivityThermal stability of metallic compounds
Chapter 19Metals and Their ReactivityReactions of metallic compoundswith acids and alkalis
Chapter 19Metals and Their ReactivityQuick Check 31. Arrange the following metals in order of their ease of forming positive ions, starting from the most difficult: lead, magnesium, sodium, iron, calcium, copper, potassium, zinc.2. State what will happen when a piece of iron is placed in a beaker of copper(II) sulphate solution. Write a chemical equation for the reaction.3. Complete the following reactions. (a) Mg(s) + ZnSO4(aq) (b) Zn(s) + Pb(NO3)2(aq) (c) Al(s)+ Zn(NO3)2(aq (d) Cu(s) + ZnSO4(aq) heat (e) ZnCO3(s) Solution (f) Mg(s) + Al2O3(s)
Chapter 19Metals and Their ReactivitySolution to Quick check 31. Copper, lead, iron, zinc, magnesium, calcium, sodium and potassium.2. The iron will turn reddish-brown as it has displaced copper from the copper(II) sulphate solution. The blue copper(II) sulphate will become pale green in colour. Fe(s) + CuSO4(aq) FeSO4(aq) + Cu(s)3. (a) Mg(s) + ZnSO4(aq) MgSO4(aq) + Zn(s) (b) Zn(s) + Pb(NO3)2(aq) Zn(NO3)2(aq) + Pb(s) (c) 2Al(s)+ 3Zn(NO3)2(aq) 2Al(NO3)3(aq) + 3Zn(s) (d) Cu(s) + ZnSO4(aq) No reaction heat (e) ZnCO3(s) ZnO(s) + CO2(g) (f) 3Mg(s) + Al2O3(s) 3MgO(s) + 2Al(s) Return
Chapter 19Metals and Their Reactivity To Learn more about Metals, click on the links below! 1. http://www.chemicalelements.com/groups/alkali.html 2. http://www.ndt- ed.org/EducationResources/CommunityCollege/Materials/Introduction /metals.htm