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Core & Extension Metals I Reactivity Series & Redox.pptx

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Core & Extension Metals I Reactivity Series & Redox.pptx

  1. 1. © 2004-09 Dorje Gurung Core & Extension Metals I: Reactivity Series & Redox
  2. 2. Core & Ext. Metals: Reactivity Series & Redox Slide 2 of 53 Learning Objectives Concepts: – Reactivity, displacement, reduction, metal, order of reactivity – redox reaction, reduction, oxidation, oxidizing agent (oxidant), reducing agent (reductant), half-equation, ionic equation Skills Core: – Place the following metals in order of reactivity: calcium, copper, (hydrogen), iron, magnesium, potassium, sodium and zinc by reference to the reactions, if any, of the metals with water or steam, dilute hydrochloric acid and the reaction of their oxides with carbon – Deduce an order of reactivity from a given set of experimental results – Place carbon and hydrogen in the reactivity series.
  3. 3. Core & Ext. Metals: Reactivity Series & Redox Slide 3 of 53 Learning Objectives Skills – Define oxidation and reduction in terms of oxygen loss/gain – Identify reduction, oxidation, reducing agent, oxidizing agent – Describe methods of rust prevention: paint and other coatings to exclude oxygen Extension: – Account for the apparent unreactivity of aluminum in terms of the oxide layer which adheres to the metal
  4. 4. Core & Ext. Metals: Reactivity Series & Redox Slide 4 of 53 Metals 80% of all elements are metals. Fig 1. Metals & non-metals in the periodic table Other common metals include iron, calcium and magnesium. Fig 2. The amount of different metals in the earths surface The most abundant metal in the earths surface is aluminum.
  5. 5. Core & Ext. Metals: Reactivity Series & Redox Slide 5 of 53 The periodic Table
  6. 6. Core & Ext. Metals: Reactivity Series & Redox Slide 6 of 53 Some General Properties Physical Properties They are usually shiny. However they may look dull if they they are covered in a layer of metal oxide. All metals will conduct electricity. All metals are good conductors of heat Most metals are malleable: they can be beaten into different shapes Many metals like copper are ductile: they can be stretched into thin wires Most metals have high melting points and boiling points Chemical Properties They lose electrons to from positively charged ions They combine with non-metals to form ionic compounds Most metals react with acids to produce a salt and hydrogen They react with oxygen to produce basic oxides
  7. 7. Core & Ext. Metals: Reactivity Series & Redox Slide 7 of 53 Reactivity Series Remember, when metals react, they lose electrons to become positively charged ions. Some metals lose electrons easily, this makes them very reactive. – For example, potassium reacts explosively with cold water and acids. Other metals react more slowly. – A piece of iron takes several days to rust when it is placed in water. A few metals, such as gold and silver are very unreactive, they do not combine with other elements, they never rust or oxidize. The Group One metals are most reactive, followed by the Group Two metals and then the transition metals. – The Metals at the bottom of each group are more reactive than the metals on the top of each group. (Do you remember why?)
  8. 8. Core & Ext. Metals: Reactivity Series & Redox Slide 8 of 53 Reactive 1. What does the word reactive actually mean? It means how easily a chemical combines with another to form a compound. In the case of a metal, it’s how easily it will lose electrons to form a cation (or the difficulty with which its ion will part with the anion to which it is bonded). 2. Why is potassium very reactive? It is very reactive because the outer electron is very easily removed.
  9. 9. Core & Ext. Metals: Reactivity Series & Redox Slide 9 of 53 Reactivity Series of metals From your Form 3 Chemistry studies of patterns of reactivity, you should know that the reactivity series is as follows: Most reactive  Least reactive Aluminium appears in the middle of the reactivity series, between magnesium and zinc. This suggests that it should corrode faster than iron, and react more quickly with acids than zinc. But aluminium does not corrode and does not react with acids as you have already noted from past experiments!
  10. 10. Core & Ext. Metals: Reactivity Series & Redox Slide 10 of 53 Reactivity of metals: Aluminum Why does aluminum appear to be very unreactive? The surface of a piece of aluminum oxidizes very quickly and becomes covered with a thin layer of aluminum oxide. The layer of aluminum oxide has the same effect as a coat of paint , protecting the aluminum beneath it. Other metals such as iron also oxide, but iron oxide is soft easily removed from the surface so it cannot protect the metal .
  11. 11. Core & Ext. Metals: Reactivity Series & Redox Slide 11 of 53 Reactivity Series The order was arrived at by observing the manner and extent of reaction of the metal – with water (or steam), – with dilute acid, – oxide with carbon, – oxide with other metals, – and with salt solution of other metals This year, we will also look at the stability of hydroxides and nitrates of the metals to heat and the metal’s reaction with oxides of other metals. Most reactive  Least reactive
  12. 12. Core & Ext. Metals: Reactivity Series & Redox Slide 12 of 53 Reaction of Metals with Water Most metals react with water; just that some react vigorously with even cold water, while others require steam. But the reaction always produces hydrogen gas. Very reactive metals like potassium will react quickly with cold water, producing a solution of potassium hydroxide and hydrogen gas. K (s) + H2O (l)  KOH (aq) + H2 (g) – The heat of the reaction is great enough to ignite the hydrogen explosively. – Sodium may also ignite as shown to the right. • The reaction is more and more violent down the group as you have already noted from your studies of the periodic table. • So the three placed in order of decreasing reactivity would be K > Na > Li.
  13. 13. Core & Ext. Metals: Reactivity Series & Redox Slide 13 of 53 Reaction of Metals with Water Less reactive metals like magnesium and calcium react very slowly with cold water (fig.1), but quickly with steam (fig.2). Solid white magnesium oxide powder and hydrogen gas and are produced. Fig. 2 Fig. 1 hydrogen
  14. 14. Core & Ext. Metals: Reactivity Series & Redox Slide 14 of 53 Reaction of Metals with Water When calcium react with water, the products are the same as when group 1 metals react wit it. Ca (s) + H2O (l)  Ca(OH)2 (aq) + H2 (g) – The resulting solution of course is limewater, which when reacted with carbon dioxide produces the white precipitate of calcium carbonate. Magnesium however does not react readily with water. It reacts instead with steam to produce magnesium oxide and hydrogen gas. Magnesium + steam  Magnesium oxide + hydrogen Mg (s) + H2O (g)  MgO (s) + H2 (g) Unreactive metals such as gold do not react with water at all. That is why gold coins recovered from old ship wrecks appear shiny and new.
  15. 15. Core & Ext. Metals: Reactivity Series & Redox Slide 15 of 53 Reaction of Metals with Water Since calcium reacts with water while magnesium requires steam, order of reactivity is therefore Ca > Mg. In other words, reactivity increases going down group 2 as well just as with group 1 metals. Placing K, Na, Ca and Mg in order we get: K > Na > Ca > Mg.
  16. 16. Core & Ext. Metals: Reactivity Series & Redox Slide 16 of 53 Reactions of metals with acid Many metals react with dilute acids to produce their respective salt and hydrogen gas. The vigor of the reaction varies with the reactivity of the metal. The more reactive the metal the more vigorous the reactivity—bubbling and heat is produced when a reaction does take place. In general: Metal + acid  salt solution + hydrogen gas Mg (s) + HCl (aq)  MgCl2 (aq) + H2 (g) Ionic equation: Metal + 2H+ (aq)  Metal ion (aq) + H2 (g) Mg(s) + 2H+ (aq)  Mg2+ (aq) + H2 (g)
  17. 17. Core & Ext. Metals: Reactivity Series & Redox Slide 17 of 53 Reactions of metals with acid The most reactive metals such as potassium, sodium and lithium react very rapidly, producing enough heat to ignite the hydrogen gas and cause an explosion. – Group 1 metals therefore are not tested with acids in a secondary lab. Less reactive metals such as iron react quite slowly with acids, but the reaction can be made faster by warming the acid gently with a bunsen burner. Copper reacts with only concentrated acids and, besides, the reaction is a little different from those of the reactive metals. Gold reacts only with a special mixture of concentrated nitric acid and sulfuric acid.
  18. 18. Core & Ext. Metals: Reactivity Series & Redox Slide 18 of 53 Reactivity series Therefore, group 1 metals are more reactive than Magnesium, Zinc, Iron and Copper. Of the metals tested, Magnesium was the most vigorous, zinc next, and then iron while copper did not even react. So therefore, of the four metals the most reactive is Magnesium, followed by Zinc, and then Iron, and lastly Copper. The reactivity series from the most to the least reactive looks like this: Potassium, Sodium, Lithium, Calcium, Magnesium, Zinc, Iron, Copper.
  19. 19. Core & Ext. Metals: Reactivity Series & Redox Slide 19 of 53 Placement of carbon in the order The experiments on the reactions of charcoal with metal oxides you performed allowed you to determine the approximate location of carbon (charcoal) in the order of reactivity.
  20. 20. Core & Ext. Metals: Reactivity Series & Redox Slide 20 of 53 Placement of carbon in the order Carbon was able to displace lead, zinc and copper from their oxides but not aluminum oxide in the experiments you performed in the laboratory. zinc oxide + Carbon  Carbon dioxide + zinc ZnO(s) + C(s)  CO2(g) + Pb(s) Copper oxide + Carbon  Carbon dioxide + copper CuO(s) + C(s)  CO2(g) + Cu(s) Aluminum oxide + Carbon  No reaction
  21. 21. Core & Ext. Metals: Reactivity Series & Redox Slide 21 of 53 Placement of carbon in the order Based on these results, it was concluded that carbon could be placed between aluminum and zinc. Displacement reactions where oxygen exchange takes place between the reactants is classified under a whole set of reaction type called redox reaction. And that is what we are going to look at next. Potassium Sodium Calcium Magnesium Aluminum Zinc Iron Copper Here
  22. 22. Core & Ext. Metals: Reactivity Series & Redox Slide 22 of 53 Redox reactions and oxygen A redox reaction is a type of chemical reaction in which oxidation and reduction occur. When iron rusts, it reacts with oxygen in air to form iron oxide, commonly called rust. Fe (s) + O2 (g)  Fe2O3 (s) Rusting of iron is an example of a redox reaction. When material made from iron (for example car body, nails, axes, railings etc) is exposed to the elements, iron rusts.
  23. 23. Core & Ext. Metals: Reactivity Series & Redox Slide 23 of 53 Redox in terms of oxygen When other metals notably group 1 elements are exposed to air they react with oxygen in air and undergoes a redox reaction. Their shiny recently-exposed surface goes grey over time (which you oberved in the lab). Li (s) + O2 (g)  Li2O (s) Na (s) + O2 (g)  Na2O (s) K (s) + O2 (g)  K2O (s) Aluminum also reacts with air forming an thin layer of oxide which prevents the rest of the aluminum from corroding. Al (s) + O2 (g)  Al2O3 (s)
  24. 24. Core & Ext. Metals: Reactivity Series & Redox Slide 24 of 53 Redox in terms of oxygen Similarly, when coal is burnt to provide fuel, then it reacts with oxygen in air and undergoes a redox reaction. C (s) + O2 (g)  CO2 (g) Carbon has undergone oxidation; it has gained oxygen. The oxygen added to an element can be obtained from another compound.
  25. 25. Core & Ext. Metals: Reactivity Series & Redox Slide 25 of 53 The Reactivity Series This happens when a metal that is higher up in the reactivity series reacts with the oxide of a less reactive element in the series, such as another metal or carbon or hydrogen (water). metals becoming more reactive Potassium Sodium Calcium Magnesium Aluminium (Carbon) Zinc Iron (Hydrogen) Copper Silver Gold
  26. 26. Core & Ext. Metals: Reactivity Series & Redox Slide 26 of 53 Oxygen from an oxide From your studies of metal reactivity, you know that a more reactive metal (or substance) will displace a less reactive metal from its oxide. Metal 1 (or substance 1) + Metal 2 oxide  Metal 1 oxide + Metal2 Al has undergone oxidation, or has been oxidized (to aluminum oxide). Oxidation is gain of oxygen. Iron(III) oxide is said to have undergone reduction, or it’s been reduced (to iron). Reduction is the loss of oxygen. For example, the thermite reaction Al(s) + Fe2O3(s)  Fe(s) + Al2O3(s) (s) 2 3(s) (s) 2 3(s) Al + Fe O Fe + Al O  Oxidation Reduction
  27. 27. Core & Ext. Metals: Reactivity Series & Redox Slide 27 of 53 Oxygen from an oxide Again, since Fe2O3 is the provider of oxygen (causing Al to get oxidized), it is referred to as the Oxidizing agent. Similarly, since Al removes oxygen from Fe2O3 (causing it to be reduced to Fe), Al is referred to as a the Reducing agent. Similarly, (s) 2 3(s) (s) 2 3(s) Al + Fe O Fe + Al O  (s) (s) (s) (s) Mg + CuO MgO + Cu  Oxidation Reduction Reducing agent Oxidizing agent
  28. 28. Core & Ext. Metals: Reactivity Series & Redox Slide 28 of 53 Oxygen from an oxide Similarly, 2CuO(s) + C(s)  2Cu(s) + CO2(g) 2Fe2O3(s) + 3C(s)  4Fe(s) + 3CO2(g) 2PbO(s) + C(s)  2Pb(s) + CO2(g) H2(g) + CuO (s)  Cu(s) + H2O (s) Here CuO has undergone reduction, and H2 oxidation. CuO loses oxygen, while H2 gains oxygen. Identify the oxidizing and reducing agents in the reactions that appear on this slide. In the last reaction, PbO has undergone reduction, and C oxidation. PbO loses oxygen, while C gains oxygen.
  29. 29. Core & Ext. Metals: Reactivity Series & Redox Slide 29 of 53 Oxygen from Water If we take water for example, any it can provide oxygen to any metal higher up in the reactivity series than hydrogen. Mg has undergone oxidation, and water is said to have undergone reduction. Reduction is the loss of oxygen. When steam is passed over magnesium, magnesium oxide and hydrogen gas is produced for example. Mg (s) + H2O (g)  MgO (s) + H2 (g) Aluminum would react in a similar manner. What is oxidizing agent and what the reducing agent in the above reaction? Calcium and the group 1 metals, as you already know, react with water in a completely different manner.
  30. 30. Core & Ext. Metals: Reactivity Series & Redox Slide 30 of 53 Redox reaction definition In terms of oxygen: – Gain of oxygen is oxidation. • That which gains (or accepts) oxygen is the reducing agent. – Loss of oxygen is reduction. • That which loses (or provides) oxygen is the oxidizing agent.
  31. 31. Core & Ext. Metals: Reactivity Series & Redox Slide 31 of 53 Redox reaction Photography, respiration, reactions in batteries, wine going off, bleaching, rusting etc. are all examples of what in chemistry we call redox reactions. Photography involves conversion of silver bromide to silver metal. Respiration involves the breakdown of glucose in the presence of oxygen to get energy. Reactions in batteries involves using the different reactivities of metals to make electrons flow through a circuit which again provides energy. Wine going off, bleaching, rusting also involve reaction with oxygen which are classified as redox reaction.
  32. 32. Core & Ext. Metals: Reactivity Series & Redox Slide 32 of 53 Another example of Redox Reaction: Rusting After: A new material (Fe2O3) is made which is brown and flaky. Before: The iron metal (Fe) is shiny and hard. We say that iron and has undergone oxidation. The definition of oxidation according to this example given here is the addition of oxygen.
  33. 33. Core & Ext. Metals: Reactivity Series & Redox Slide 33 of 53 Prevention of Rusting Rusting of iron and steel can be prevented by any method that stops iron from coming in contact with oxygen. One of the ways to do so is to paint it. Paint essentially forms a barrier between oxygen in the air and the iron. Other methods which also work under the same principle involves coati it with oil and grease which work particular well with moving parts, and plastic (PVC) coating, used on items such as refrigerators and lawn chairs. Still others involve electroplating (with layer of chromium or tin) and galvanizing (usually with zinc) (see Electricity & Chemistry: Electroplating).
  34. 34. Core & Ext. Metals: Reactivity Series & Redox Slide 34 of 53 Summary The reactivity series lists metals (and two nonmetals) in the order of their relative reactivity. Displacement reactions provide evidence for position of a metal and those of hydrogen and carbon. The displacement reaction may be – Between a metal and salt solution of another – Between a metal and the oxide of another metal or that of hydrogen or carbon, – Reaction with acid.
  35. 35. Core & Ext. Metals: Reactivity Series & Redox Slide 35 of 53 Summary The more reactive the metal that higher up in the reactivity series it will appear. The more reactive metal/non-metal will displace a less reactive metal/nonmetal from its salt solution or its oxide. When oxygen exchange takes place between substances, the reaction can be classified as a redox reaction. The one that accepts the oxygen is said to have undergone oxidation and therefore referred to as the reducing agent. The one that loses (provides) the oxygen is said to have undergone reduction and therefore referred to as the oxidizing agent. Aluminum appears to be unreactive due to the protective layer of oxide that coats its surface, which also prevents it from rusting further.
  36. 36. Core & Ext. Metals: Reactivity Series & Redox Slide 36 of 53 Paper 2 Practice Questions 1. J05/2/6d. The information below shows the reactivity of chromium, copper and iron with warm hydrochloric acid. chromium – few bubbles of gas produced every second copper – no bubbles of gas produced iron – many bubbles of gas produced every second Put these three metals in order of their reactivity with hydrochloric acid. Most reactive  …………………………. …………………………. Least Reactive  …………………………. [1]
  37. 37. Core & Ext. Metals: Reactivity Series & Redox Slide 37 of 53 Paper 2 Practice Questions 2. N04/2/1e. State three properties shown by all metals. [3] 3. J03/2/6 (c) Uranium is between magnesium and zinc in the reactivity series. Equal sized strips of magnesium, uranium and zinc were placed in hydrochloric acid. The hydrochloric acid was the same concentration. The results are shown in the table.
  38. 38. Core & Ext. Metals: Reactivity Series & Redox Slide 38 of 53 Paper 2 Practice Questions (i) Complete the result for uranium and hydrochloric acid. [1] metal observations on adding to hydrochloric acid magnesium many bubbles of gas produced very rapidly and magnesium dissolves quickly uranium zinc a few bubbles produced at a steady rate and zinc dissolves slowly
  39. 39. Core & Ext. Metals: Reactivity Series & Redox Slide 39 of 53 Paper 2 Practice Questions 4. N01/2/6. In the ‘thermit’ reaction, aluminium powder reacts violently with iron(III) oxide. A magnesium ribbon is lit to start the reaction. The reaction gives out a great deal of heat. The equation for the reaction is: 2Al(s) + Fe2O3(s)  Al2O3(s) + 2Fe(s)
  40. 40. Core & Ext. Metals: Reactivity Series & Redox Slide 40 of 53 Paper 2 Practice Questions (a) Complete the following sentence about the ‘thermit’ reaction using words from the list. added electrolysed neutralised oxidised reduced In the ‘thermit’ reaction, the aluminium is ................................... to aluminium oxide and the iron(III) oxide is ................................... to iron. [2] (b) Aluminium oxide which has been heated to a high temperature is called fused aluminium oxide. Fused aluminium oxide does not react with hydrochloric acid. Iron reacts with hydrochloric acid.
  41. 41. Core & Ext. Metals: Reactivity Series & Redox Slide 41 of 53 Paper 2 Practice Questions (i) What would you observe when hydrochloric acid is added to a mixture of fused aluminium oxide and iron? [1] (ii) After reaction with hydrochloric acid, the mixture contains fused aluminium oxide solid and a solution of iron(II) chloride. Describe with the help of a labelled diagram, how you would separate the aluminium oxide from the iron(II) chloride solution. [4]
  42. 42. Core & Ext. Metals: Reactivity Series & Redox Slide 42 of 53 Paper 2 Practice Questions (c) The magnesium ribbon used to start the ‘thermit’ reaction burns in oxygen and gives out heat. What term describes a reaction that gives out heat? [1] (d) In an oxyacetylene torch, oxygen is used with acetylene to produce a flame with a temperature of about 3000°C. State one use of this flame. [1]
  43. 43. Core & Ext. Metals: Reactivity Series & Redox Slide 43 of 53 Paper 3 Practice Questions 1. J05/3/6. The position of aluminium in the reactivity series of metals is shown below. Magnesium Aluminium Zinc Copper (b) Aluminium reacts very slowly with aqueous copper(II) sulphate. 2Al(s) + 3CuSO4(aq)  Al2(SO4)3(aq) + 3Cu(s) (i) Which of the two metals has the greater tendency to form ions? [1] (ii) Describe what you would see when this reaction occurs. [1]
  44. 44. Core & Ext. Metals: Reactivity Series & Redox Slide 44 of 53 Paper 3 Practice Questions (iii) Explain why aluminium reacts so slowly. [1] (c) Complete the following table by writing “reaction” or “no reaction” in the spaces provided. [2]
  45. 45. Core & Ext. Metals: Reactivity Series & Redox Slide 45 of 53 Paper 3 Practice Questions 2. N02/3/5d. Steel may be coated with another metal, eg zinc or chromium, or with a polymer, eg poly(chloroethene), to prevent rusting. (i) Suggest a property of poly(chloroethene) that makes it suitable for this purpose. [1] (ii) Explain why the steel will rust when the protective coating of chromium or polymer is broken. [1] (iii) When the protective layer of zinc is broken, the steel still does not rust. Suggest an explanation. [2]
  46. 46. Core & Ext. Metals: Reactivity Series & Redox Slide 46 of 53 Paper 3 Practice Questions 3. N01/3/4. (d) A use of zinc is galvanising. When the zinc layer is broken, the steel is exposed. Explain why the exposed steel does not rust. [3]
  47. 47. Core & Ext. Metals: Reactivity Series & Redox Slide 47 of 53 Paper 6 questions 1. J04/6/2. The four tubes show an investigation of rusting. Each one of these four tubes contains a nail and the reagents indicated.
  48. 48. Core & Ext. Metals: Reactivity Series & Redox Slide 48 of 53 Paper 6 questions (a) Predict the order in which rust would appear. First Second [1] (b) Explain your prediction. [2]
  49. 49. Core & Ext. Metals: Reactivity Series & Redox Slide 49 of 53 Paper 6 questions 2. N02/6/4. An investigation was carried out on the reactions of four different metals. Equal masses of copper, magnesium, iron and zinc were used. Experiment 1 A 15 cm3 sample of dilute sulphuric acid was added to each of four boiling tubes. The initial temperature of the acid was measured. Zinc was added to the first tube, iron to the second tube, magnesium to the third tube and copper to the fourth tube. The maximum temperature reached in each tube was measured and any observations were recorded in the table. (a) Use the thermometer diagrams to complete the results table.
  50. 50. Core & Ext. Metals: Reactivity Series & Redox Slide 50 of 53
  51. 51. Core & Ext. Metals: Reactivity Series & Redox Slide 51 of 53 Paper 6 questions Use your results and observations to answer the following questions. (i) Which metal is most reactive with sulphuric acid? [1] (ii) Give two reasons why you chose this metal. 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [2] (iii) Name the gas given off. [1] The reaction between magnesium and aqueous copper(II) sulphate was then investigated.
  52. 52. Core & Ext. Metals: Reactivity Series & Redox Slide 52 of 53 Paper 6 questions Experiment 2 A 5 cm3 sample of aqueous copper(II) sulphate was measured into a test- tube. The initial temperature of the solution was measured. Magnesium powder was added to the test-tube and the maximum temperature reached was measured. Use the thermometer diagrams to complete the results table.
  53. 53. Core & Ext. Metals: Reactivity Series & Redox Slide 53 of 53 Paper 6 questions (b) How do your observations show that the reaction of magnesium with aqueous copper(II) sulphate is exothermic? [1] (c) What type of exothermic reaction occurs when magnesium is added to aqueous copper(II) sulphate? [1] (d) Use your results from Experiments 1 and 2 to put the four metals in order of reactivity. least reactive ................................ ................................. ................................. most reactive ................................. [1]

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