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Redox presentation 11 july 2011
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Redox presentation 11 july 2011

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basic concept in chemistry

basic concept in chemistry

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  • 1. REDOX 1.A.DEFINATION Transfer of electrons Oxidation is reduction is PROCESS WHERE ELECTRON IS RELEASED PROCESS WHERE ELECTRON IS GAINED
  • 2.
    • change in oxidation number
    • Oxidation is
    • reduction is
    PROCESS WHERE OXIDATION NUMBER INCREASE PROCESS WHERE OXIDATION NUMBER DECREASE
  • 3.
    • b.Calculate the oxidation number of
    • i.Chromium in K2Cr2O7
    • ii. Chlorine in ClO4-
    • iii.Oxygen in H3O+.
    2(+1) + 2x +7(-2) =0. , Cr = +6 x +4(-2) =-1. , Cl= +7 3(+1) +x =+1. , O= -2
  • 4.
    • c.IUPAC nomenclature
    • i.K2CrO4
    • ii.MgSO4
    Potasium Chromate (VI) Magnesium sulphate(VI)
  • 5.
    • iii.HNO3
    • iv.HNO2
    nitric acid (V) Nitric acid (III)
  • 6.
    • d. Redox & non redox reaction.
    • reasons
    • Zn + CuSO4  Cu + ZnSO4
    • ii. ZnCO3  ZnO + CO2
    Redox reaction because the oxidation number of Zn Change from 0 to +2 Non Redox reaction because the oxidation number of Zn no change,( from +2 to +2)
  • 7.
    • B) Br2 + 2KI  I2 + 2KBr
    • i.name of this reaction
    • ii.change in oxidation number of bromine
    • iii. change in oxidation number of iodine
    Displacement of halogen From 0 to -1 From -1 to 0
  • 8.
      • iv.half equation for
    • Oxidation reaction .
    • Reduction reaction
    • Write the overall equation
    2I -  I 2 + 2e Br 2 + 2e  2Br - Br 2 + 2I -  2Br - + I 2
  • 9.  
  • 10. Question 2 Iron(II) chloride reacts with chlorine in a redox reaction
  • 11. Name the reaction above
    • CHANGE OF IRON(II) ION TO IRON(III) ION
    • REDOX (TYPE OF REACTION)
  • 12. Write out the rough equation first to show the products and the reactants
    • 2FeCl 2 + Cl 2  2FeCl 3
  • 13. Place arrows to show oxidation reaction and reduction reaction on your answer on your answer in b) above
    • 2FeCl 2 + Cl 2  2FeCl 3
    reduction oxidation
  • 14. What substance is oxidized and why?
    • Iron (II) ions, oxidation number of iron increase from +2 to +3
  • 15. What substance is reduced and why?
    • Chlorine, because oxidation number of chlorine decrease from
    • 0 to -1
  • 16. Write the half equation for oxidation
    • Fe 2+  Fe 3+ + e
  • 17. Write the half equation for reduction
    • Cl 2 + 2e  2Cl -
  • 18. Write the overall reaction
    • 2Fe 2+ + Cl 2  2Fe 3+ + 2Cl -
  • 19. What is the oxidizing agent? And why
    • Chlorine water,
    • because it oxidised iron(II) ions to iron(III) ions
  • 20. What is the reducing agent? And why
    • Iron(II) ions,
    • because it reduced chlorine
    • to chloride ions
  • 21. State 2 observations in this experiment
    • Green solution turns brown
  • 22. Describe how you would confirm the presence of the product, that is iron(III) ion
    • Add a few drops of NaOH solution, brown precipitate is formed
  • 23. State another substance that can replace chlorine in the above experiment
    • Any oxidising agent
    • Bromine water //
    • acidified KMnO 4 //
    • acidified K 2 Cr 2 O 7
  • 24.  
  • 25. a) Which electrode behave as negative electrode? Why? - + 3.
  • 26. a) Which electrode behave as negative electrode? Why? A because iodide ions undergoes oxidation where it lose electrons, the electrons are negatively charged causing it to be negative electrode
  • 27. b) Draw direction for electron flow in the outer circuit
  • 28. c) Write out the rough equation first to show reactants and the products d) Put arrows on your equation above to show oxidation reaction and reduction reaction on your answer in c) above OXIDATION REDUCTION
  • 29. e) What substance is oxidized? Explain your answer in terms of electron transfer Iodide ions because it lose electron
  • 30. f) What substance is reduced? Explain your answer in terms of electron transfer Dichromate ions because it accept electrons
  • 31.
    • g) Write half equations for:
    • Oxidation
    • Reduction
  • 32. h) Write overall equation 6I - + Cr 2 O 7 2- + 14H +  2Cr 3+ + 7H 2 O + 3I 2
  • 33. i) State your observations during the experiment at i)Rod A ii)Rod B Dark brown solution formed Orange solution turns to green solution
  • 34. j)How do you test the presence of iodine formed at rod A? OR Add 2 cm 3 tetrachloromethane to iodine solution, shake well then purple solution formed at lower layer Add a few drops of starch solution, a blue-black solution formed
  • 35.  
  • 36.
    • Test tube C, D. Presence of Fe 2+
    • In C and D, silver and lead are less electropositive than iron.
    • So,iron nail (Fe) is oxidised to Fe 2+ .
    • In test tube E, iron nail also
    • oxidised but takes longer time
    After 3 days, which test tubes show blue colour?, why?
  • 37. Which test tubes show pink colour? Why?
    • Test tube A and B.
    • Presence of OH -
    • Because Mg and Zn are more electropositive than Fe.
    • So, Mg atom and Zn atom will lose electrons
    • oxygen and water gain these electrons to form OH - This cause the pink colour of phenolphthalein
  • 38. What is the function of the jelly solution?
    • To trap the colour formed during corrosion process
  • 39. Which of the above metals prevent rusting of iron nails?
    • Metals above iron in ECS Magnesium and Zinc metals.
    Which of the above metals increase the rusting of iron
    • Metals below iron in ECS
    • Lead metal and silver metal
  • 40. Why does the iron surface at the centre of water droplet behave as anode (negative electrode)? Because here iron atom release electron
  • 41. Why does the iron surface at the edge of water droplet behave as cathode( positive electrode)?
    • Because oxygen and water gain the electrons here.
  • 42. What happen at the anode?
    • Iron atom loses electron to form iron (II) ions.
    • So Oxidation occur.
  • 43. Write half equation at the anode Fe Fe 2+ + 2e Where does the iron(II) ions formed from the reaction go to? Iron (II) ions dissolve in water
  • 44. Where does the electrons released by the metal iron go to?
    • Electron moves to the edge of water droplet ( cathode)
    What happens at the cathode? At cathode, electrons are received by oxygen and water molecules to form hydroxide ions
  • 45. Write half equation at the cathode
    • O 2 + 2H 2 O +4e 4OH -
  • 46. Write equations to form rust when iron(II) ion formed at the anode combine with hydroxide ions formed at the cathode ,  
    • Fe 2+ + 2OH - Fe(OH) 2
    Fe(OH) 2 Fe 2 O 3 .xH 2 O

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