Redox reaction1 ANALYTICAL CHEMISTRY Chem. 243 Redox titration Chapter 6

Redox reaction2 Quantitative Volumetric Analysis Last measurement is volume Neutralization titrations Oxidation titrations Precipitation titrations Complexometric titrations.

Redox reaction3 This lecture covers three topics: Redox Titrations. Assignment of oxidation numbers Balancing of redox equations

Redox reaction4 Redox Reactions. Oxidation Reduction Oxidation-Reduction Reactions

Redox reaction5 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. Oxidation-Reduction Reactions

Redox reaction6 6 Oxidation: Gain of oxygen Loss of electrons Reduction: Loss of oxygen Gain of electrons Increase in oxidation number Decrease in oxidation number Oxidation-Reduction Reactions

Redox reaction7 7 LEO the lion says GER! o s e l e c t r o n s x i d a t i o n a i n l e c t r o n s e d u c t i o n GER! Oxidation-Reduction Reactions Na Na + + e - Cl + e - Cl - Negative charge represents electron richness Positive charge represents electron deficiency

Redox reaction8 8 Oxidation-Reduction Reactions (electron transfer reactions) 2Mg 2Mg e - O 2 + 4e - 2O 2- Oxidation half-reaction (lose e - ) Reduction half-reaction (gain e - ) 2Mg + O 2 + 4e - 2Mg O e - 2Mg + O 2 2MgO

Redox reaction9 9 2Mg(s) + O 2 (g)  2MgO(s) Oxidised – gains oxygen Must be a redox! Mg  Mg 2+ O  O 2- Put the e - in. +2e - Oxidised – loss of e - Reduced – gain of e -

Redox reaction10Redox reaction10

Redox reaction11Redox reaction11 Cu(s) + 2AgNO 3 (aq)  Cu(NO 3 ) 2 (aq) + 2Ag(s) 2Ag +  2Ag Cu  Cu 2+ Complete the half- equations +2e - Oxidised? Reduced? Oxidised – loss of e - Reduced – gain of e - Oxidation-Reduction Reactions

Redox reaction12Redox reaction12 Zn (s) + CuSO 4 (aq) ZnSO 4 (aq) + Cu (s) Zn is oxidizedZn Zn e - Cu 2+ is reducedCu e - Cu Zn is the reducing agent Cu 2+ is the oxidizing agent 4.4 Copper wire reacts with silver nitrate to form silver metal. What is the oxidizing agent in the reaction? Cu (s) + 2AgNO 3 (aq) Cu(NO 3 ) 2 (aq) + 2Ag (s) Cu Cu e - Ag + + 1e - AgAg + is reducedAg + is the oxidizing agent Oxidation-Reduction Reactions Cu is the reducing agentCu is oxidized

Redox reaction13 Nuggets of redox processes Where there is oxidation there is always reduction Oxidizing agentReducing agent Is itself reducedIs itself oxidized Gains electronsLoses electrons Causes oxidationCauses reduction

Redox reaction14Redox reaction14 Oxidation number The charge the atom would have in a molecule (or an ionic compound) if electrons were completely transferred. 1.Free elements (uncombined state) have an oxidation number of zero. Na, Be, K, Pb, H 2, O 2, P 4 = 0 2.In monatomic ions, the oxidation number is equal to the charge on the ion. Li +, Li = +1; Fe 3+, Fe = +3; O 2-, O = -2 3.The oxidation number of oxygen is usually –2. In H 2 O 2 and O 2 2- it is –1.

Redox reaction15Redox reaction15 H 2 (g) + ½ O 2 (g)  H 2 O(g) O H Oxidised? H – increase in oxidation number Reduced? O – decrease in oxidation number Oxidation number

Redox reaction16 Oxidation number 4.Group IA metals are +1, IIA metals are +2 and fluorine is always –1.

Redox reaction17 ns 1 ns 2 ns 2 np 1 ns 2 np 2 ns 2 np 3 ns 2 np 4 ns 2 np 5 ns 2 np 6 d1d1 d5d5 d 10 4f 5f Ground State Electron Configurations of the Elements

Redox reaction Cations and Anions Of Representative Elements

Redox reaction19Redox reaction19 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. HCO 3 - O = -2H = +1 3x(-2) ? = -1 C = +4 Oxidation numbers of all the elements in HCO 3 - ? 6. Oxidation numbers do not have to be integers. Oxidation number of oxygen in the superoxide ion, O 2 -, is -½. Oxidation number

Redox reaction20Redox reaction20 NaIO 3 Na = +1 O = -2 3x(-2) ? = 0 I = +5 H = +1 2x(+1) + ? = 0 O 2 = -2 K 2 Cr 2 O 7 O = -2K = +1 7x(-2) + 2x(+1) + 2x(?) = 0 Cr = +6 Oxidation numbers of all the elements in the following ? Oxidation number H2O2H2O2

Redox reaction21Redox reaction21 H2C2O4H2C2O4 H = +1 O = -2 1(2) +? +4x(-2) = 0 2C = +6 IF 7 F = -1 7x(-1) + ? = 0 I = +7 K MnO 4 O = -2K = +1 4x(-2) + 1x(+1) + (?) = 0 Mn = +7 Oxidation numbers of all the elements in the following ? Oxidation number (-8) + (+1) + (?) = 0

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

Redox reaction24 Oxidation Numbers The oxidation numbers of atoms in a compound add up to zero. F O-2 H+1 Cl Oxidation state of C in CO 2 ? ? – 4 = 0 ? = +4 Put the +! 24Redox reaction

25 Oxidation Numbers The oxidation numbers of atoms in a compound add up to zero. F O-2 H+1 Cl Oxidation state of Mg in MgCl 2 ? +2 25Redox reaction

26 Oxidation Numbers The oxidation numbers of atoms in a compound add up to zero. F O-2 H+1 Cl Oxidation state of N in NH 3 ? -3 26Redox reaction

27 Oxidation Numbers The oxidation numbers of atoms in an ion add up to the charge on the ion. F O-2 H+1 Cl Oxidation state of S in S 2- ? -2 27Redox reaction

chemical reaction in aqueous solution 28 Types of Oxidation-Reduction Reactions Oxidation Reduction Reaction Combination Reaction Decomposition Reaction Displacement Reaction

chemical reaction in aqueous solution 29 Combination Reaction A + B C 2Al + 3Br 2 2AlBr Types of Oxidation-Reduction Reactions More than one reactant, single product +2 +1

chemical reaction in aqueous solution 30 Types of Oxidation-Reduction Reactions 2KClO 3 2KCl + 3O 2 C A + B Decomposition Reaction Single reactant, more than one product

chemical reaction in aqueous solution 31 Displacement Reaction A + BC AC + B Cl 2 + 2KBr 2KCl + Br 2 Halogen Displacement Halogen Displacement Types of Oxidation-Reduction Reactions One element displaces another from a compound

chemical reaction in aqueous solution 32 Displacement Reaction A + BC AC + B TiCl 4 + 2Mg Ti + 2MgCl 2 Metal Displacement Metal Displacement Types of Oxidation-Reduction Reactions

chemical reaction in aqueous solution 33 Displacement Reaction A + BC AC + B Sr + 2H 2 O Sr(OH) 2 + H 2 Hydrogen Displacement Types of Oxidation-Reduction Reactions Hydrogen Displacement

chemical reaction in aqueous solution 34 Displacement Reaction A + BC AC + B TiCl 4 + 2Mg Ti + 2MgCl 2 Metal Displacement Metal Displacement Types of Oxidation-Reduction Reactions

Redox reaction35Redox reaction35 Ca 2+ + CO 3 2- CaCO 3(s) NH 3 + H + NH 4 + Zn + 2HCl ZnCl 2 + H 2 Ca + F 2 CaF 2 Precipitation Acid-Base Redox (H 2 Displacement) Redox (Combination) Classify the following reactions.

Redox reaction36 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 reaction37 Oxidation Numbers The oxidation numbers of atoms in an ion add up to the charge on the ion. F O-2 H+1 Cl Oxidation state of N in NH 4 + ? -3 37Redox reaction

38 Problem 12-5: Redox Titration- I Volume (L) of KMnO 4 Solution Moles of KMnO 4 M (mol/L) Molar ratio in redox rxn. Chemical Formulas Moles of CaC 2 O 4 Problem: Calcium Oxalate was precipitated from 1.00 mL blood by the addition of Sodium Oxalate so the Ca 2+ 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 M KMnO 4 to reach the endpoint via the rxn. of Fig a) Calculate the moles of Ca 2+. b) Calculate the Ca 2+ conc. in blood. Plan: a) Calculate the moles of Ca 2+ in the H 2 SO 4 solution (and blood sample). b) Convert the Ca 2+ conc.into units of mg Ca 2+ / 100 mL blood. Moles of Ca +2 a) b) c)

Redox reaction39 Equation: 2 KMnO 4 (aq) + 5 CaC 2 O 4 (aq) + 8 H 2 SO 4 (aq) 2 MnSO 4 (aq) + K 2 SO 4 (aq) + 5 CaSO 4 (aq) + 10 CO 2 (g) + 8 H 2 O(l) Problem 12-5: Redox Titration - Calculation - II a) Moles of KMnO 4 b) Moles of CaC 2 O 4 c) Moles of Ca +2

Redox reaction40 Problem 12-5: Redox Titration - III Moles of Ca 2+ / 1 mL of blood Moles of Ca 2+ / 100 mL blood Mass (g) of Ca 2+ / 100 mL blood Mass (mg) of Ca 2+ / 100 mL blood multiply by 100 a) Calc of mol Ca 2+ per 100 mL M (g/mol) b) Calc of mass of Ca 2+ per 100 mL 1g = 1000mg c) convert g to mg!

Redox reaction41 Titration of Oxalic acid Vs KMnO 4 Primary standard Secondary standard 16 H + (aq) + 2 MnO 4 - (aq) + 5 C 2 O 4 -2 (aq)  2 Mn +2 (aq) + 10 CO 2 (g) + 8 H 2 O(l) 5 C 2 O 4 2- ions are oxidized by 2 MnO 4 - ions to 10 CO 2 molecules. Conversely 2 MnO 4 - is reduced by 5 C 2 O 4 2- ions to 2Mn 2+ ions.

Redox reaction42 Well done!