REDOX REACTIONS Oxidation and Reduction
Objectives <ul><li>Define oxidation and reduction (redox) in terms of oxygen / hydrogen gain/loss. </li></ul><ul><li>Defin...
Redox reactions around us… <ul><li>Combustion of gasoline </li></ul><ul><li>Browning of a freshly cut apple </li></ul><ul>...
 
Introduction <ul><li>Redox reactions involve a transfer of electrons. </li></ul><ul><li>Oxidation is always accompanied by...
What is oxidation?  A substance is oxidised if one the following happens after a reaction: It  gains oxygen  or It  loses ...
Oxidation — Gain of Oxygen  2Ca(s)  +  O 2 (g)     CaO(s) By the end of the reaction, calcium has gained oxygen. Calcium ...
Oxidation — Gain of Oxygen  CH 4 (g) + 2O 2 (g)    CO 2 (g) + 2H 2 O( l ) The  carbon  atom in methane has gained oxygen ...
Oxidation — Loss of Hydrogen  A substance is oxidised if it loses hydrogen.  2NH 3 (g)  +  3CuO(s)     N 2 (g)  +  3Cu(s)...
Oxidation — Loss of Electrons When a substance loses electrons during a reaction, it is oxidised. Oxidation reactions can ...
Oxidation — Loss of Electrons Mg     Mg 2+   +  2e – Each magnesium atom  loses 2 electrons  to form a magnesium ion. <ul...
Oxidation — Loss of Electrons The copper atom has been oxidised to the copper(II) ion. In the reaction Cu(s)  +  2AgNO 3 (...
Oxidation — Increase in Oxidation State The  oxidation state   is the “ charge ” an atom of an element would have if it ex...
Various Definitions of Oxidation & Reduction Redox Oxidation Reduction Gain  in Oxygen Loss  in Hydrogen Loss  in Electron...
Mnemonics for Redox –  OIL - RIG OIL - RIG :  Oxidation is Loss  –  Reduction is Gain Redox Oxidation Reduction Gain   in ...
Test your understanding
<ul><li>For the following reactions, identify which species is   oxidized   and which species   is   reduced : </li></ul><...
<ul><li>For the following reactions, identify which species is oxidized and which species is reduced: </li></ul><ul><li>2N...
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Redox Reactions

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Oxidation and Reduction - What are they?

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Redox Reactions

  1. 1. REDOX REACTIONS Oxidation and Reduction
  2. 2. Objectives <ul><li>Define oxidation and reduction (redox) in terms of oxygen / hydrogen gain/loss. </li></ul><ul><li>Define redox in terms of electron transfer and changes in oxidation state. </li></ul><ul><li>Describe the use of aqueous potassium iodide and acidified potassium dichromate (VI) in testing for oxidising and reducing agents from the resulting colour changes </li></ul>
  3. 3. Redox reactions around us… <ul><li>Combustion of gasoline </li></ul><ul><li>Browning of a freshly cut apple </li></ul><ul><li>Corrosion of metals </li></ul><ul><li>Photosynthesis </li></ul><ul><li>Removal of stains at home </li></ul><ul><li>Lightening of hair colour (bleaching) </li></ul>
  4. 5. Introduction <ul><li>Redox reactions involve a transfer of electrons. </li></ul><ul><li>Oxidation is always accompanied by reduction </li></ul>
  5. 6. What is oxidation? A substance is oxidised if one the following happens after a reaction: It gains oxygen or It loses hydrogen or It loses electrons or It increases its oxidation state.
  6. 7. Oxidation — Gain of Oxygen 2Ca(s) + O 2 (g)  CaO(s) By the end of the reaction, calcium has gained oxygen. Calcium has been oxidised to calcium oxide . This process is called oxidation .
  7. 8. Oxidation — Gain of Oxygen CH 4 (g) + 2O 2 (g)  CO 2 (g) + 2H 2 O( l ) The carbon atom in methane has gained oxygen and has been oxidised to carbon dioxide . The hydrogen atom in methane has also gained oxygen . Hydrogen has been oxidised to water.
  8. 9. Oxidation — Loss of Hydrogen A substance is oxidised if it loses hydrogen. 2NH 3 (g) + 3CuO(s)  N 2 (g) + 3Cu(s) + 2H 2 O(g) Ammonia has lost hydrogen. It has been oxidised to nitrogen.
  9. 10. Oxidation — Loss of Electrons When a substance loses electrons during a reaction, it is oxidised. Oxidation reactions can take place even if there is no oxygen or hydrogen present . <ul><ul><ul><li>Mg(s) + C l 2 (g)  MgC l 2 (s) </li></ul></ul></ul>Look at the equation above. In the next slide, you see how electrons are lost in this reaction.
  10. 11. Oxidation — Loss of Electrons Mg  Mg 2+ + 2e – Each magnesium atom loses 2 electrons to form a magnesium ion. <ul><ul><li>In this reaction, magnesium atoms has been oxidised to form magnesium ions. </li></ul></ul>Mg(s) + C l 2 (g)  MgC l 2 (s)
  11. 12. Oxidation — Loss of Electrons The copper atom has been oxidised to the copper(II) ion. In the reaction Cu(s) + 2AgNO 3 (aq)  Cu(NO 3 ) 2 (aq) + 2Ag(s) which substance is oxidised? The ionic equation for this reaction is Cu(s) + 2Ag + (aq)  Cu 2+ (aq) + 2Ag(s) <ul><ul><li>Each copper atom loses 2 electrons and becomes a copper(II) ion. </li></ul></ul>
  12. 13. Oxidation — Increase in Oxidation State The oxidation state is the “ charge ” an atom of an element would have if it existed as an ion in a compound (even if it is actually covalently bonded). The oxidation state is also known as oxidation number .
  13. 14. Various Definitions of Oxidation & Reduction Redox Oxidation Reduction Gain in Oxygen Loss in Hydrogen Loss in Electron (s) Loss in Oxygen Gain in Hydrogen Gain in Electron (s ) Increase in Oxidation State Decrease in Oxidation State 1 2 3 4
  14. 15. Mnemonics for Redox – OIL - RIG OIL - RIG : Oxidation is Loss – Reduction is Gain Redox Oxidation Reduction Gain in Oxygen Loss in Hydrogen Loss in Electron (s) Loss in Oxygen Gain in Hydrogen Gain in Electron (s )
  15. 16. Test your understanding
  16. 17. <ul><li>For the following reactions, identify which species is oxidized and which species is reduced : </li></ul><ul><li>PbO(s) + H 2 (g)  Pb(s) + H 2 O(g) </li></ul><ul><li>Answer: PbO [R], H 2 [O] </li></ul><ul><li>Fe 2 O 3 (s) + 3CO(g)  2Fe(s) + 3CO 2 (g) </li></ul><ul><li>Answer: Fe 2 O 3 [R], CO [O] </li></ul><ul><li>Mg(s) + Cl 2 (g)  MgCl 2 (s) </li></ul><ul><li>Answer: Mg [O], Cl 2 [R] </li></ul>
  17. 18. <ul><li>For the following reactions, identify which species is oxidized and which species is reduced: </li></ul><ul><li>2NH 3 (g)+ 3Cl 2 (g)  N 2 (g) + 6HCl (g) </li></ul><ul><li>Answer: Cl 2 [R], NH 3 [O] </li></ul><ul><li>SnO 2 (g) + 2C (s)  Sn (s) + 2CO (g) </li></ul><ul><li>Answer: SnO 2 [R], C [O] </li></ul><ul><li>WO 3 (s) + 3H 2 (g)  W (s) + 3H 2 O (g) </li></ul><ul><li>Answer: WO 3 [R], H 2 [O] </li></ul>

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