10 Reduction and Oxidation
Oxidation Numbers <ul><li>Group 1 ox no = +1 </li></ul><ul><li>Group 2 ox no = +2 </li></ul><ul><li>Group 3 ox no = +3 </l...
<ul><li>Oxidation numbers add up to 0 for neutral molecule </li></ul><ul><li>e.g. NaCl  Na = +1 CL = -1 </li></ul><ul><li>...
<ul><li>Find ox no of underlined elements </li></ul><ul><li>N 2 H 4  Cr O 4 -2   Cl O 3 4-  N H 4 +  V O 2 + </li></ul>N =...
<ul><li>Oxidation is any process where there is an increase in an oxidation state </li></ul><ul><li>Oxidation is  loss  of...
<ul><li>O  oxidation </li></ul><ul><li>I  is  </li></ul><ul><li>L  loss </li></ul><ul><li>R reduction  </li></ul><ul><li>I...
<ul><li>increase in oxidation state </li></ul>(loss of electrons) -3  -2  -1  0  +1  +2  +3  +4  +5  +6  +7  decrease in o...
<ul><li>Examples of oxidation </li></ul><ul><li>Fe 2 +  -   e     Fe 3+   </li></ul><ul><li>Cu  -  2e     Cu 2+ </li></u...
<ul><li>Deduce which of these reactions are redox reactions. Assign oxidation no’s to each atom. In the case of redox reac...
<ul><li>We can add 2 half equations together to make a full equation. Oxidation and reduction must both occur together.  <...
<ul><li>So we can add  </li></ul><ul><li>Fe 2 +  -   e     Fe 3+  and </li></ul><ul><li>MnO 4 -   +  5e     Mn 2+ </li><...
<ul><li>1)  Fe 2 +  -   e     Fe 3+  </li></ul><ul><li>2)  MnO 4 -   +  5e     Mn 2+ </li></ul><ul><li>In order to add t...
<ul><li>Form the full equation for the reaction that occurs between potassium manganate(VII) and hydrogen peroxide </li></...
<ul><li>Write balance ion equations for the following and determine whether oxidation or reduction occurs </li></ul><ul><l...
<ul><li>Construct full equations from the half equations in the data sheets for the following reactions. </li></ul><ul><li...
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10 Reduction And Oxidation

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10 Reduction And Oxidation

  1. 1. 10 Reduction and Oxidation
  2. 2. Oxidation Numbers <ul><li>Group 1 ox no = +1 </li></ul><ul><li>Group 2 ox no = +2 </li></ul><ul><li>Group 3 ox no = +3 </li></ul><ul><li>H ox no = +1 except in an alkali metal hydride e.g. NaH where it is -1 </li></ul><ul><li>O ox no = -2 except in a peroxide where it is -1 </li></ul><ul><li>Halides usually -1 (except when bonded to other halogens or oxygen) </li></ul>
  3. 3. <ul><li>Oxidation numbers add up to 0 for neutral molecule </li></ul><ul><li>e.g. NaCl Na = +1 CL = -1 </li></ul><ul><li>MgCl 2 Mg = +2 Cl = -1 </li></ul><ul><li>AlF 3 Al = +3 F = -1 </li></ul><ul><li>For a charged ion ox no’s add up to the charge </li></ul><ul><li>MnO 4 - </li></ul>Mn = +7 O = -2
  4. 4. <ul><li>Find ox no of underlined elements </li></ul><ul><li>N 2 H 4 Cr O 4 -2 Cl O 3 4- N H 4 + V O 2 + </li></ul>N = -2 Cr = +6 Cl = +2 N = -3 V = +5
  5. 5. <ul><li>Oxidation is any process where there is an increase in an oxidation state </li></ul><ul><li>Oxidation is loss of electrons </li></ul><ul><li>Reduction is any process where there is a decrease in oxidation state </li></ul><ul><li>Reduction is gain of electrons </li></ul>
  6. 6. <ul><li>O oxidation </li></ul><ul><li>I is </li></ul><ul><li>L loss </li></ul><ul><li>R reduction </li></ul><ul><li>I is </li></ul><ul><li>G gain </li></ul>
  7. 7. <ul><li>increase in oxidation state </li></ul>(loss of electrons) -3 -2 -1 0 +1 +2 +3 +4 +5 +6 +7 decrease in oxidation state (Gain of electrons)
  8. 8. <ul><li>Examples of oxidation </li></ul><ul><li>Fe 2 + - e  Fe 3+ </li></ul><ul><li>Cu - 2e  Cu 2+ </li></ul><ul><li>Example of reduction </li></ul><ul><li>Fe 3+ + e  Fe 2+ </li></ul><ul><li>MnO 4 - + 5e  Mn 2+ </li></ul><ul><li>These are called half equations </li></ul>In any reaction involving oxidation and reduction there must be a species giving electrons and another species gaining electrons. Hence the term redox reaction.
  9. 9. <ul><li>Deduce which of these reactions are redox reactions. Assign oxidation no’s to each atom. In the case of redox reactions identify the oxidising and reducing agents. </li></ul><ul><li>1) Ca (s) + Cl 2(g)  CaCl 2(s) </li></ul><ul><li>2) Cl 2(g) + H 2 S (g)  2HCl (g) + S (s) </li></ul><ul><li>3) Ba(NO 3 ) 2(aq) + Na 2 SO 4(aq)  BaSO 4(s) + 2NaNO 3(aq) </li></ul><ul><li>4) Ni (s) + CuSO 4(s)  NiSO 4(aq) + Cu (s) </li></ul><ul><li>5) Cl 2 O 7(g) + H 2 O (l)  2HClO 4(aq) </li></ul><ul><li>6) 2CuCl (aq)  CuCl 2(aq) + Cu (s) </li></ul>
  10. 10. <ul><li>We can add 2 half equations together to make a full equation. Oxidation and reduction must both occur together. </li></ul><ul><li>The species donating electrons is called the reducing agent </li></ul><ul><li>The species receiving electrons is called the oxidising agent </li></ul>
  11. 11. <ul><li>So we can add </li></ul><ul><li>Fe 2 + - e  Fe 3+ and </li></ul><ul><li>MnO 4 - + 5e  Mn 2+ </li></ul><ul><li>to make a full equation </li></ul><ul><li>In this example Mn 7+ is being reduced and is the oxidising agent. It is receiving electrons from the Fe 2+ </li></ul><ul><li>Fe 2+ is being oxidised and is the reducing agent. It is giving electrons to the Mn 7+ . </li></ul>
  12. 12. <ul><li>1) Fe 2 + - e  Fe 3+ </li></ul><ul><li>2) MnO 4 - + 5e  Mn 2+ </li></ul><ul><li>In order to add the 2 half equations we first have to balance the electrons by multiplying 1) by 5 </li></ul><ul><li>5Fe 2 + - 5e  5 Fe 3+ </li></ul><ul><li>MnO 4 - + 5e  Mn 2+ </li></ul>5Fe 2+ + MnO 4 -  5Fe 3+ + Mn 2+
  13. 13. <ul><li>Form the full equation for the reaction that occurs between potassium manganate(VII) and hydrogen peroxide </li></ul><ul><li>The half equations are; </li></ul><ul><li>MNO 4 - (aq) + 8H + (aq) + 5e  Mn 2+ (aq) + 4H 2 O (l) </li></ul><ul><li>H 2 O 2(aq)  O 2(g) + 2H + (aq) + 2e </li></ul>2MnO 4 - (aq) + 6H + (aq) + 5H 2 O 2(l)  2Mn 2+ (aq) + 8H 2 O (l) + 5O 2(g)
  14. 14. <ul><li>Write balance ion equations for the following and determine whether oxidation or reduction occurs </li></ul><ul><li>chlorine to chloride ions </li></ul><ul><li>oxygen to oxide ions </li></ul><ul><li>aluminium to aluminium ions </li></ul><ul><li>magnesium to magnesium ions </li></ul><ul><li>tin(IV) ions to tin (II)ions </li></ul><ul><li>chromium(II) to chromium(III) ions </li></ul>O 2 + 4e  2O 2- ox no 0 to -2 reduction Al -3e  Al 3+ ox no 0 to +3 oxidation Mg -2e  Mg 2+ ox no 0 to +2 oxidation Sn 4+ +2e  Sn 2+ ox no +4 to +2 reduction Cl 2 + 2e  2Cl - ox no 0 to -1 reduction
  15. 15. <ul><li>Construct full equations from the half equations in the data sheets for the following reactions. </li></ul><ul><li>H 2 O 2 reacting with either Fe 2+ or Fe 3+ </li></ul><ul><li>S 2 O 3 2- reacting with either I 2 or I - </li></ul><ul><li>MnO 4 - with either Sn 2+ or Sn 4+ </li></ul>
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