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ANALYTICAL CHEMISTRY

ANALYTICAL CHEMISTRY. Chem. 243. Chapter 6. Redox titration. Quantitative Volumetric Analysis Last measurement is volume. Complexometric titrations. Neutralization titrations. Precipitation titrations. Oxidation titrations. This lecture covers three topics:. Redox Titrations .

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ANALYTICAL CHEMISTRY

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  1. ANALYTICAL CHEMISTRY Chem. 243 Chapter 6 Redox titration Redox reaction

  2. Quantitative Volumetric Analysis Last measurement is volume Complexometric titrations. Neutralization titrations Precipitation titrations Oxidation titrations Redox reaction

  3. This lecture covers three topics: • Redox Titrations. • Assignment of oxidation numbers • Balancing of redox equations Redox reaction

  4. Oxidation-Reduction Reactions Redox Reactions. Reduction Oxidation Redox reaction

  5. Oxidation-Reduction Reactions Oxidation and reduction go hand in hand. In a reaction, if there is an atom undergoing oxidation, there is probably another atom undergoing reduction. When there is an atom that donates electrons, there is always an atom that accepts electrons. Electron transfer happens from one atom to another. Redox reaction

  6. Oxidation-Reduction Reactions • Oxidation: • Gain of oxygen • Loss of electrons • Reduction: • Loss of oxygen • Gain of electrons Increase in oxidation number Decrease in oxidation number 6 Redox reaction Redox reaction

  7. Oxidation-Reduction Reactions LEO the lion says GER! xidation eduction lectrons lectrons ain ose GER! Na Na+ + e- Cl + e- Cl - Positive charge represents electron deficiency Negative charge represents electron richness 7 Redox reaction Redox reaction

  8. 2Mg 2Mg2+ + 4e- O2 + 4e- 2O2- 2Mg + O2 + 4e- 2Mg2+ + 2O2- + 4e- 2Mg + O2 2MgO Oxidation-Reduction Reactions (electron transfer reactions) Oxidation half-reaction (lose e-) Reduction half-reaction (gain e-) 8 Redox reaction Redox reaction

  9. Oxidised – gains oxygen 2Mg(s) + O2(g)  2MgO(s) Must be a redox! Mg  Mg2+ Oxidised – loss of e- +2e- Put the e- in. O  O2- Reduced – gain of e- +2e- 9 Redox reaction Redox reaction

  10. 10 Redox reaction Redox reaction

  11. Oxidation-Reduction Reactions Cu(s) + 2AgNO3(aq)  Cu(NO3 )2(aq) + 2Ag(s) Complete the half-equations Oxidised? Reduced? Cu Cu2+ Oxidised – loss of e- +2e- 2Ag+ 2Ag Reduced – gain of e- +2e- 11 Redox reaction Redox reaction

  12. Oxidation-Reduction Reactions Cu (s) + 2AgNO3 (aq) Cu(NO3)2 (aq) + 2Ag (s) Zn (s) + CuSO4 (aq) ZnSO4 (aq) + Cu (s) Cu2+ + 2e- Cu Copper wire reacts with silver nitrate to form silver metal. What is the oxidizing agent in the reaction? Cu Cu2+ + 2e- Zn Zn2+ + 2e- Ag+ + 1e- Ag Zn is the reducing agent Zn is oxidized Cu2+is reduced Cu2+ is the oxidizing agent Cu is oxidized Cu is the reducing agent Ag+is reduced Ag+ is the oxidizing agent 12 Redox reaction Redox reaction 4.4

  13. Nuggets of redox processes Where there is oxidation there is always reduction Redox reaction

  14. Oxidation number The charge the atom would have in a molecule (or an ionic compound) if electrons were completely transferred. • Free elements (uncombined state) have an oxidation number of zero. Na, Be, K, Pb, H2, O2, P4 = 0 • In monatomic ions, the oxidation number is equal to the charge on the ion. Li+, Li = +1; Fe3+, Fe = +3; O2-, O = -2 • The oxidation number of oxygen isusually–2. In H2O2 and O22- it is –1. 14 Redox reaction Redox reaction

  15. Oxidation number H2(g) + ½ O2(g)H2O(g) H +1 0 O 0 -2 Oxidised? Reduced? O – decrease in oxidation number H – increase in oxidation number 15 Redox reaction Redox reaction

  16. Oxidation number 4 .Group IA metals are +1, IIA metals are +2 and fluorine is always –1. Redox reaction

  17. ns2np6 ns1 ns2np1 ns2np2 ns2np3 ns2np4 ns2np5 ns2 d10 d1 d5 4f 5f Ground State Electron Configurations of the Elements Redox reaction

  18. -1 -2 -3 +1 +2 +3 Cations and Anions Of Representative Elements Redox reaction

  19. Oxidation number Oxidation numbers of all the elements in HCO3- ? 5. The sum of the oxidation numbers of all the atoms in a molecule or ion is equal to the charge on the molecule or ion. 6. Oxidation numbers do not have to be integers. Oxidation number of oxygen in the superoxide ion, O2-, is -½. HCO3- O = -2 H = +1 3x(-2) + 1 + ? = -1 C = +4 19 Redox reaction Redox reaction

  20. Oxidation number Oxidation numbers of all the elements in the following ? H2O2 H = +1 2x(+1) + ? = 0 O2 = -2 K2Cr2O7 NaIO3 O = -2 K = +1 O = -2 Na = +1 3x(-2) + 1 + ? = 0 7x(-2) + 2x(+1) + 2x(?) = 0 I = +5 Cr = +6 20 Redox reaction Redox reaction

  21. Oxidation number Oxidation numbers of all the elements in the following ? IF7 F = -1 7x(-1) + ? = 0 I = +7 KMnO4 H2C2O4 O = -2 K = +1 O = -2 H = +1 1(2) +? +4x(-2) = 0 4x(-2) + 1x(+1) + (?) = 0 2C = +6 (-8) + (+1) + (?) = 0 Mn = +7 21 Redox reaction Redox reaction

  22. Chromium gives great example of different oxidation numbers • Different oxidation states of chromium have different colors • Chromium (II) chloride = blue • Chromium (III) chloride = green • Potassium chromate = yellow • Potassium dichromate = orange

  23. Oxidation Numbers • The oxidation numbers of atoms in a compound add up to zero. Oxidation state of C in CO2? ? – 4 = 0 ? = +4 Put the +! 24 Redox reaction Redox reaction

  24. Oxidation Numbers • The oxidation numbers of atoms in a compound add up to zero. Oxidation state of Mg in MgCl2? +2 25 Redox reaction Redox reaction

  25. Oxidation Numbers • The oxidation numbers of atoms in a compound add up to zero. Oxidation state of N in NH3? -3 26 Redox reaction Redox reaction

  26. Oxidation Numbers • The oxidation numbers of atoms in an ion add up to the charge on the ion. Oxidation state of S in S2-? -2 27 Redox reaction Redox reaction

  27. Types of Oxidation-Reduction Reactions chemical reaction in aqueous solution

  28. A + B C 2Al + 3Br2 2AlBr3 Types of Oxidation-Reduction Reactions Combination Reaction More than one reactant, single product +3 -1 0 0 +2 +1 chemical reaction in aqueous solution

  29. C A + B 2KClO3 2KCl + 3O2 Types of Oxidation-Reduction Reactions Decomposition Reaction Single reactant, more than one product +1 +5 -2 0 +1 -1 chemical reaction in aqueous solution

  30. A + BC AC + B Cl2 + 2KBr 2KCl + Br2 Types of Oxidation-Reduction Reactions Displacement Reaction One element displaces another from a compound +1 0 -1 0 Halogen Displacement 0 -1 -1 0 Halogen Displacement chemical reaction in aqueous solution

  31. A + BC AC + B TiCl4 + 2Mg Ti + 2MgCl2 Types of Oxidation-Reduction Reactions Displacement Reaction +2 0 +2 0 Metal Displacement +4 0 0 +2 Metal Displacement chemical reaction in aqueous solution 4.4

  32. A + BC AC + B Sr + 2H2O Sr(OH)2 + H2 Types of Oxidation-Reduction Reactions Displacement Reaction +1 +2 0 0 Hydrogen Displacement 0 +1 0 +3 Hydrogen Displacement chemical reaction in aqueous solution

  33. A + BC AC + B TiCl4 + 2Mg Ti + 2MgCl2 Types of Oxidation-Reduction Reactions Displacement Reaction +2 0 +2 0 Metal Displacement +4 0 0 +2 Metal Displacement chemical reaction in aqueous solution 4.4

  34. Ca2+ + CO32- CaCO3(s) NH3 + H+ NH4+ Classify the following reactions. Zn + 2HCl ZnCl2 + H2 Ca + F2 CaF2 Precipitation Acid-Base Redox (H2 Displacement) Redox (Combination) 35 Redox reaction Redox reaction

  35. What is redox titration? A TITRATION WHICH DEALS WITH A REACTION INVOLVING OXIDATION AND REDUCTION OF CERTAIN CHEMICAL SPECIES. What is a titration? The act of adding standard solution in small quantities to the test solution till the reaction is complete is termed titration. Redox reaction

  36. Oxidation Numbers • The oxidation numbers of atoms in an ion add up to the charge on the ion. Oxidation state of N in NH4+? -3 37 Redox reaction Redox reaction

  37. Problem 12-5: Redox Titration- I Problem: Calcium Oxalate was precipitated from 1.00 mL blood by the addition of Sodium Oxalate so the Ca2+ conc. in the blood could be determined. This precipitate was dissolved in a sulfuric acid solution, which then required 2.05 mL of 4.88 x 10-4 M KMnO4 to reach the endpoint via the rxn. of Fig. 4.14. a) Calculate the moles of Ca2+. b) Calculate the Ca2+ conc. in blood. Plan: a) Calculate the moles of Ca2+ in the H2SO4 solution (and blood sample). b) Convert the Ca2+ conc.into units of mg Ca2+/ 100 mL blood. Volume (L) of KMnO4 Solution a) M (mol/L) Moles of KMnO4 Molar ratio in redox rxn. b) Moles of CaC2O4 c) Chemical Formulas Moles of Ca+2 Redox reaction

  38. Problem 12-5: Redox Titration - Calculation - II Equation: 2 KMnO4 (aq) + 5 CaC2O4 (aq) + 8 H2SO4 (aq) 2 MnSO4 (aq) + K2SO4 (aq) + 5 CaSO4 (aq) + 10 CO2 (g) + 8 H2O(l) a) Moles of KMnO4 b) Moles of CaC2O4 c) Moles of Ca+2 Redox reaction

  39. Problem 12-5: Redox Titration - III Moles of Ca2+/ 1 mL of blood multiply by 100 a) Calc of mol Ca2+ per 100 mL Moles of Ca2+/ 100 mL blood M (g/mol) b) Calc of mass of Ca2+ per 100 mL Mass (g) of Ca2+/ 100 mL blood 1g = 1000mg c) convert g to mg! Mass (mg) of Ca2+ / 100 mL blood Redox reaction

  40. Titration of Oxalic acid Vs KMnO4 Primary standard Secondary standard 16 H+(aq) + 2 MnO4-(aq) + 5 C2O4-2(aq)2 Mn+2(aq) + 10 CO2(g) + 8 H2O(l) 5 C2O42- ions are oxidized by 2 MnO4- ions to 10 CO2 molecules. Conversely 2 MnO4- is reduced by 5 C2O42- ions to 2Mn2+ ions. Redox reaction

  41. Well done! Redox reaction

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