Redox Reaction

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2 Definitions of redox reaction

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Redox Reaction

  1. 1. By Mr Jeremy Lee<br />Redox Reaction<br />
  2. 2. REDOX stands for REDuction & OXidation<br />Both reduction and oxidation occur simultaneously.<br />What is redox reaction?<br />Substance that reduces another substance is called reducing agent<br />A Substance that oxidizes another substance is called oxidizing agent<br />
  3. 3. Which substance is being oxidized and reduced?2Na + Br2 2NaBr<br />Sodium<br />Bromine<br />Bromine gas become bromide ions<br />Chemical equation<br />Br2 + 2e- 2Br -<br />The 2 electrons that sodium metal loses has been taken by bromine gas to become bromide ions<br />Sodium metal become sodium ions<br />Chemical equation<br />2Na (s) 2Na + + 2e-<br />OR<br />Na (s) Na + + e- (Simplified)<br />Sodium metal has loses 2 electrons to become sodium ions<br />
  4. 4. More example : Metal and acid reactionZn + 2H+ Zn2+ + H2<br />Zinc metal<br />Hydrogen Ion (from acid)<br />Hydrogen ions becomes Hydrogen gas<br />2H+ + 2e- H2<br />Hydrogen ions will receive the 2 electrons to become hydrogen gas.<br />Zinc metal has become Zinc ions <br />ZnZn2+ + 2e-<br />It becomes a Zinc ions after it happens<br />
  5. 5. From the 2 examples, what are the conditions to consider a substance to become oxidized or reduced?<br />
  6. 6. Oxidation number<br />What are oxidation numbers?<br />- Oxidation state or oxidation number is a + or - value given to an element to represent the charge of an atom or ion after Redox reaction.<br />- Even for atoms inside a covalent compound, they contains oxidation number.<br />
  7. 7. Overall charge of this compound is zero<br />KMnO4<br />Examples<br />Now you see it, now you don’t<br />Potassium permanganate<br />Potassium has a charge of +1 and permanganate ion has a charge of -1<br />Potassium permanganate (purple) can be reduced to manganese ion<br /> Mn2+(Colourless!)<br />Decrease in oxidation state from +7 to become +2<br />REDUCTION!<br />Oxygen carries a -2 charge each<br />-2 X 4 = -8 <br />+1<br />?<br />
  8. 8. Potassium dichromate<br />Overall charge is Zero<br />K2Cr2O7<br />Chromate ion has a charge of -2<br />Cr2O72-<br />Each chromium has a charge of +6<br />Potassium dichromate (orange) can be reduced to chromate ion (green), Cr3+<br />Cr2O72−(aq) + 14H+ + 6e− -> 2Cr3+(aq) + 7H2O<br />Decrease in oxidation state <br />Reduction!!!!<br />Now you see it, Now you don’t<br />Potassium Dichromate<br />-2 X 7 = -14<br />+1 X 2 = +2<br />?<br />
  9. 9. Iodide Ions<br />Sodium Iodide<br />Aqueous Sodium iodide (colourless), NaI, can be turned into brown solution.<br /> How?<br />Solution contains iodide ions ( I- )<br /> Iodide ion can be turned into Iodine ( I2 )<br /> 2I-(aq) I2 (aq) + 2e-<br />Iodine is brown and has a oxidation state of zero<br />Increase in oxidation state from -1 to O. oxidation has taken place<br />

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