Oxidizing and Reducing Agents in Chemical Reactions

1. Problem: Identify the oxidizing and reducing agent in each of the Rx: a) Zn(s) + 2 HCl(aq) ZnCl2 (aq) + H2 (g) b) S8 (s) + 12 O2 (g) 8 SO3 (g) c) NiO(s) + CO(g) Ni(s) + CO2 (g)

2. Answers to Problems in Lecture #12 • (b) The ox. no. of oxygen is –2; the ox. no. of N is +4 • (c) The ox. no. of H is +1, the ox. no. of each O is –2, the sulfur atom is +6 • a • (b) S8 is the reducing agent and O2 is the oxidizing agent • (c) CO is the reducing agent and NiO is the oxidizing agent • NH3 + CH4 -> HCN + 3H2 • 3CuS + 8NO3- + 8H3O+ -> 3Cu2+ + 3(SO4)2- +8NO + 12H2O • (a) 2.50 x 10 -6 mol Ca2+ in H2SO4 soln; 2.50 x 10 -4 mol Ca2+ in blood; (b) 10.0 mg Ca2+/100 mL blood HCl is the oxidizingagent, andZnis the reducing agent!

3. For each of the compounds of sulfur below, write the oxidation number of sulfur in the compound?  answered 1 year ago • S ...............  SCl2 ..........  SO2 .......... SO3 ..........  H2SO4 ...... chapter 8

4. For each of the compounds of sulfur below, write the oxidation number of sulfur in the compound?  answered 1 year ago • S ............... 0 SCl2 .......... +2 SO2 .......... +4 SO3 .......... +6 H2SO4 ...... +6 chapter 8

5. Welcome to Chem 2210 Complex metric Reaction and Titrations ANALYTICAL CHEMISTRY Chapter 8

6. ANALYTICAL CHEMISTRY: deals with methods for identifications and determiningthe chemical composition of samples. Quantitative Analysis determining how much the amount present in The sample Qualitative Analysis present in sampleidentify what material Neutralization reaction Gravimetric Last measurement is mass Volumetric Last measurement is volume Oxidation reaction Precipitation reaction Instrumental Method Complexometric reaction Electro analytical Electroanalytical based upon electron-transfer Spectrophotometeric Interaction of light and matter Lecture 1

7. Basic Concepts and Terms • Complex • Important of ComplexationTitrations • Complex-Formation Titrations • FORMING COMPLEXES • Producing Soluble Forming Insoluble Species • Chelation in Medicine • EDTA • Some applications in human life

8. Basic Concepts and Terms EDTA a. EDTA Complexes b. Metal ion indicator c.Indicators for EDTA Titrations d. EDTA Titration Techniques e. ORGANIC COMPLEXING AGENTS

9. Complex (coordinate compound) • Coordinate covalent bonds: a bond formed when both electrons of the bond are donated by one atom. • Ag+ + 2(:NH3) [H3N: Ag :NH3]+ • Electron configuration of Ag [Kr]4d105s15P0 • Ag+ [Kr]4d105s0 5P0 • Sp hybrid orbitals: accommodate 2 pairs of electrons. Linear • Complex ion: A metal ion with Lewis base attached to it through coordinate covalent bond. Complex (Coordinate compound): a compound consisting either of complex ions and other ions of opposite charge or of neutral complex species.

10. Complex metric Reactions and Titrations Complex-formation reactions are widely used in analytical chemistry. Complex metric Titrations: method allow an accurate determination of a great number of metal cation. One of the first uses of these reagents was for titrating cations (metals). In addition many complexes are colored or absorb ultraviolet radiation; the formation of these complexes is often the basis for spectrophotometric determinations. Some complexes are sparingly soluble and can be used in gravimetric analysis. . chapter 8

11. Complexation Reactions and Titrations Complexes are also widely used for 1.extracting cations from one solvent to another And 2.for dissolving insoluble precipitates chapter 8

12. Complex-Formation TitrationsGeneral Principles • Most metal ions form coordination compounds or (complexes) with electron-pair donors (ligands) • Mn+ + qLm- MLqn-mq Kf = [MLqn-mq]/[Mn+][Lm-]q • The number of covalent bonds formed is called the “coordination number” (e.g. 2,4,6) • e.g., Cu2+ has coordination number of 4 • Cu2+ + 4 NH3 Cu(NH3)42+ • Cu2+ + 4 Cl- Cu(Cl)42- chapter 8

13. FORMING COMPLEXES The donor species, or ligand is an ion as CN- , Cl- or a neutral molecule as NH3,H2O which contain unshared electron pair and can form complex with metal ion. The number of covalent bonds that a cation tends to form with electron donors is its coordination number. Typical values for coordination numbers are two, four, and six. The species formed as a result of coordination can be electrically positive, neutral, or negative. chapter 8

14. FORMING COMPLEXES • The central atom, • (usually) a metal cation, accepts the pair of electrons from the "donor molecule or ion" to form a coordinate covalent bond. • Co 3+ + 6 NH3 <==> Co(NH3)6+3 • Central atom= Co 3+ • Ligand= :NH3 • Coordination number = 6 Example chapter 8

15. FORMING COMPLEXES Types of Ligand • Unidentate Ligand A ligand that has a single donor group, (unshared electron pair) and donate it to metal ion such as ammonia, CN- , Cl- ,NO3 – • CN- is a common monodentate ligand, binding to a metal ion through one atom (C) • polydentate Ligand A ligand that has tow or more donor group (unshared electron pair) and donate it to metal ion such as glycine, which has two groups available for covalent bonding, is called bidenate. Tridentate, tetradentate, pentadentate and hexadentate chelating agents are also known • A ligand that can attach to a metal by more than one atom is multidentate or a chelating ligand chapter 8

16. Example 2 • 􀂾Unidentate Ligand, :NH3, :I • [Co(NH3)6]2+ , [CuI2]- • 􀂾Bidentate Ligand, glycine chapter 8

17. 􀂾Hexadentate Ligand: EDTA=Y [CoY]- chapter 8

18. Structure of a Metal/EDTA Chelate Octahedron Hexadentate chapter 8

19. Producing Soluble Compelxes Complexation reactions involve a metal ion M reacting with a ligand L to form a complex ML. M + L ML Complexation reactions occur in a stepwise fashion, and the reaction above is often followed by additional reactions: ML + L ML2 ML2 + L ML3 MLn-1 + L MLn Unidentate ligands invariably add in a series of steps. With multidentate ligands, the maximum coordination number of the cation may be satisfied with only one or a few added ligands. chapter 8

20. Producing Soluble Compelxes The equilibrium constants for complex formation reactions are generally written as formation constants. M + 2L ML2 M + 3L ML3 M + nL MLn The overall formation constants are products of the stepwise formation constants for the individual steps leading to the product. 2 3 n chapter 8

21. chapter 8

22. chapter 8

23. Forming Insoluble Species The addition of ligands to a metal ion may result in insoluble species, such as the familiar nickel-dimethylglyoxime precipitate. In many cases,the intermediate uncharged complexes in the stepwise formation scheme may be sparingly soluble, whereas the addition of more ligand molecules may result in soluble species. AgCl is insoluble, but addition of large excess of Cl- produces soluble AgCl2-, AgCl32-, and AgCl43-. chapter 8

24. Forming Insoluble Species The formation of soluble complexes can be used to control the concentration of free metal ions in solution and thus control their reactivity. chapter 8

25. Chelation in Medicine • Chelation therapy was first introduced in Germany in the 1930’s to combat heavy metal poisoning. • First used for good in the U.S.A. in the late forties. • Utilized in medical treatments to help remove lead from the systems of patients. • EDTA is the chelation agent of choice. chapter 8

26. EDTA Complexes • Equilibrium constant for the reaction of a metal with a ligand is called the formation constant. • M+n     +     Y-4   MYn-4 • Kf = (MYn-4)/(M+n)(Y-4) • Pb+2  +  CaY-2  PbY- +  Ca+2 •     K ~ 108  • The Pb+2 ion replaces the Ca+2 ion because K f for the lead complex is greater than the calcium complex chapter 8

27. EDTA • Ethylediaminetetraacetic acid • Most widely used chelating agent • Forms 1:1 complexes • Through titration or indirect reactions, EDTA can quanitatively measure nearly all elements. chapter 8

28. Ethylenediaminetetraacetic Acid (EDTA) Ethylenediaminetetraacetic acid which is commonly shortened to EDTA, is the most widely used complexometric titrant. Fully protonated EDTA has the structure The EDTA molecule has six potential sites for bonding a metal ion: the four carboxyl groups and the two amino groups, each of the latter with an unshared pair of electrons. Thus, EDTA is a hexadentate ligand.? chapter 8

29. EDTA Complexes • Equilibrium constant for the reaction of a metal with a ligand is called the formation constant. • M+n     +     Y-4   MYn-4 • Kf = (MYn-4)/(M+n)(Y-4) • Pb+2  +  CaY-2  PbY- +  Ca+2 •     K ~ 108  • The Pb+2 ion replaces the Ca+2 ion because K f for the lead complex is greater than the calcium complex chapter 8

30. Metal Ion Indicators • Compounds whose color changes when they bind to a metal ion. • The color change singles the end point • Most indicators can only be used in a certain pH range. chapter 8

31. Metal Ion Indicators As titrants, multidentate ligands, particularly those having four or six donor groups, have two advantages over their unidentate counterparts. First, they generally react more completely with cations and thus provide sharper end points. Second, they ordinarily react with metal ions in a single-step process,( whereas complex formation with unidentate ligands usually involves two or more intermediate species). chapter 8

32. Metal Ion Indicators The metal complexes of Eriochrome Black T(ECT) are generally red, as is H2In-. Thus, for metal-ion detection, it is necessary to adjust the pH to 7 or above so that the blue form of the species, HIn2-, predominates in the absence of a metal ion. Until the equivalence point in a titration, the indicator complexes the excess metal ion so that the solution is red. With the first slight excess of EDTA, the solution turns blue as a consequence of the reaction MIn- + HY3- HIn2- + MY2- red blue chapter 8

33. Indicators for EDTA Titrations Indicators are organic dyes that form colored chelates with metal ions in a pM range that is characteristic of the particular cation and dye. The complexes are often intensely colored and are discernible to the eye at concentrations in the range of 10-6 to 10-7 M. Eriochrome Black T is a typical metal-ion indicator used in the titration of several common cations. H2O + H2In- HIn2- + H3O+ K1 = 5 X 10-7 red blue H2O + HIn2- In3- + H3O+ K2 = 2.8 X 10-12 blue orange The acids and their conjugate bases have different colors. chapter 8

34. chapter 8

35. EDTA Titration Techniques • Direct titration: analyte is titrated with standard EDTA. • Back titration: a known excess of EDTA is added to the analyte. • Displacement titration: For metal ions that do not have a satisfactory indicator. • Indirect titration: Anions that precipitate with certain metal ions. chapter 8

36. ORGANIC COMPLEXING AGENTS • Ethylediaminetetraacetic acid EDTA. H4Y • Disodium Ethylediaminetetraacetate dihydrate Na2H2Y.2H2O • Nitrilotriacetic acid (NTA) H3X chapter 8

37. ORGANIC COMPLEXING AGENTS EDTA Is a Tetrabasic Acid The dissociation constants for the acidic groups in EDTA H4Y are K1 = 1.02 X 10-2, K2 = 2.14 X 10-3, K3 = 6.92 X 10-7, and K4 = 5.50 X 10-11 . It is of. The various EDTA species are often abbreviated H4Y, H3Y-, H2Y2-, HY3-, and Y4-. chapter 8

38. chapter 8

39. Reagents for EDTA Titrations the dihydrate of the sodium salt, Na2H2Y.2H2O, are commercially available in reagent quality. Under normal atmospheric conditions, the dihydrate, Na2H2Y.2H2O, contains 0.3% moisture in excess of the stoichiometric amount. This excess is sufficiently reproducible to permit use of a corrected weight of the salt in the direct preparation of a standard solution. The pure dihydrate can be prepared by drying at 80oC for several days in an atmosphere of 50% relative humidity. chapter 8

40. ORGANIC COMPLEXING AGENTS Nitrilotriacetic acid (NTA) chapter 8

41. chapter 8

42. Some applications in human life • Complexometric is widely used in the medical industry because of the micro liter-size sample involved

43. Some applicationsin human life • Complexometric Titration and Water Hardness: Complex metric titration is an efficient method for determining the level of hardness of water. Caused by تراكم accumulation of mineral ions, pH of water is increased

44. Zinc in Water The traces of zinc in water can be determined with complexometric titration

45. Zinc in Food Certain foods contain zinc in small amounts. Oystersالمحار and other seafood, meat, liver, eggs, milk and brewer's yeast.الخميرة Zinc deficiency is rare. It occurs when there is : • Excess alcohol • Excess exercises as sweat استنزافdepletes zinc stores • A strict vegetarian dietاتباع نظام غذائي نباتي صارم

46. Zinc in the Body • Reduces zinc-containing. enzyme, carbonic anhydrase in red blood cells. Important of ZINC • Guard against infections. وقاية من العدوى . • Repair wounds. إصلاح الجروح . • Brain development. نمو الدماغ • Smell sensation. إحساس الشم

47. Zinc in the Body • Beef contains the most amount of vitamins. • The average adult man is gets about 90% of the recommended level of zinc; women, 25%. Kids are also below the recommended level.