Redox titration

Redox titration

• 1.
  REDOX TITRATIONS SHILPA JOY ASSISTANTPROFESSOR DEPARTMENT OF CHEMISTRY KURIAKOSE ELIAS COLLEGE MANNANAM
• 2.
  REDOX TITRATIONS Oxidation –reduction titration –based on the redox reaction between analyte solution and titrant . Eg; Permagnometric titration we can estimate the H2O2 / ferrous iron by titrating with potassium permaganate which a powerful oxidizing agent , especially in acidic solution(sulphuric acid) Species titrated Species formed H2O2 O2 Fe +2 Fe +3 H2C2O4 CO2
• 3.
   The intenselycoloured MnO4 - ion is reduced to colorless Mn2+  Adv- self indicator  at the end point , the color of MnO4 - quickly disappears and reduced to Mn2+  at the end point all the reducing agents has been used up, so the next drop of MnO4 - solution is sufficient to cause an easily detected color change, faint pink .
• 4.
  W C at the endpoint , the oxidicing agent (MnO4 - ) and reducing agent (H2O2 , Fe +2 ) have reacted in exactly in proportion to their stoichiometry in the balanced equation MnO4 - + 8H + + 5e Mn 2+ + H2O E0 = 1.51 V 2KMnO4 +3H2SO4 K2SO4+2MnSO4+3H2O+5[O] Cr2O7 2- + 14H+ + 6e 2Cr 3+ + 7H2O E0 = 1.23 V K2Cr7O7 +4H2SO4 K2SO4+ Cr 2(SO4 ) 2 +4H2O+3[O] Orange green
• 5.
  If the redoxion does not produce any color change , an indicator should be used in the titration. Eg; starch –if the titrant is iodine
• 6.
  Titration curve Titration of ferrousion with ceric ion Equivalence point-point of inflection –steep raise in emf Indicator phenanthroline
• 7.
  MnO4 - + 8H++ 5e Mn2+ +4 H2O (Mn7+ to Mn2+) Fe2+ Fe+3 + e MnO4 - + 8H+ +5 Fe2+ Mn2+ +4 H2O + Fe+3 MnO4 –effective oxidizing agent- in acidic medium, it is necessary to add excess acid to the conical flask before carrying out the titration. Sulphuric acid is used HCI – NOT …reducing agent Titrations involving MnO4-
• 8.
  Cr2O7 2- + 14H+ +6e 2Cr 3+ + 7H2O Cr(IV)-Cr(III) K2 Cr2O7 2- act as an oxidizing agent in acidic medium Cr2O7 2- + 14H + + 6Fe 2+ 2Cr 3+ + 7H2 O + 6Fe 3+ at the end point Orange color changes to green if Colourless – diphenyl amine indicator ( colourless to purple) Titrations involving Cr2O7 2-
• 9.
  Redox indicators oxidation reductionindicator an indicator that undergoes definite color change at a specific electrode potential Fast and reversible color change – oxidation reduction equilibrium for an indicator redox system to be established very fast. Few organic redox systems
• 10.
  Highly coloured substancesthat may be reversibly oxidized or reduced and changes color upon oxidation and reduction. In ox + ne- +nH+ In redx Each redox indicator changes color over a certain potential range Hence indicator must have transition potential corresponding closely to the equivalence point potential of the transition.
• 11.
  • phenanthrolineMetal organic complex •Methylene blueTrue organic redox syastem Redox indicators may be pH dependent or independent
• 12.
  indicator EO V COLOUROF OXIDIZED FORM COLOUR OF REDUCED FORM 1,10 Phenanthroline +1.06 cyan red Sodium diphenyl sulphonate +0.84 Red-violet colourless diphenylamine +0.76 violet colourless Redox indicators pH dependent
• 13.
  Redox indicators pHdependent indicator EO V pH = 0 EO V pH = 7 COLOUR OF OXIDIZED FORM COLOUR OF REDUCED FORM Methylene blue +.53 +.01 Blue colourless