Lecture 8 - Lecture 9 Complexometric Titrations Chapter 13:...

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Anal Chem 251 Lect 9 Complexometric Titrations 1 Lecture 9 Complexometric Titrations Chapter 13: Problems 13:1,8,9,13 Corresponding Lab: Ca+ and Mg2= in Seawater
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Anal Chem 251 Lect 9 Complexometric Titrations 2 Complexometric Titrations The formation of well-defined (that means of known stoichiometry) complex ion by the reaction of metal ions (Lewis acids) with electron pair donor ligands (Lewis bases) with large equilibrium constants, constitutes the basis for complexometric titrations.
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Anal Chem 251 Lect 9 Complexometric Titrations 3 General Considerations H + + OH - H 2 O K = 1x 10 14 =1/k w Acid Base Cu2+ 4:NH 3 Cu(NH 3 ) 4 2+ K =8.1x10 12 Lewis Lewis acid base Ag+ + 2 :CN: - Ag(CN) 2- K =1.0 x10 21 Lewis Lewis acid base
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Anal Chem 251 Lect 9 Complexometric Titrations 4 Review - First Definition of Acid/Base Classical Definition (Arrhenius) of Acids and Bases • In the classical definition, acids and bases are defined according to their formulas and their behavior in water: •A n a c i d is a substance that has H in its formula and dissociates in water to yield H 3 O + •Ab
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Anal Chem 251 Lect 9 Complexometric Titrations 5 Review Second Definition of Acid/Base - Brønsted-Lowry Acid-Base Definition An acid is a proton donor, any species which donates a H + . A base is a proton acceptor, any species which accepts a H + . An acid must contain H in its formula. HNO 3 , H2PO4- A base must contain a lone pair of electrons to bind the H + ion. NH 3 CO 3 2- An acid-base reaction can now be viewed from the standpoint of the reactants AND the products. An acid reactant will produce a base product and the two will constitute an acid-base conjugate pair.
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Anal Chem 251 Lect 9 Complexometric Titrations 6 Review Third Definition of Acids and Bases, Lewis Acids and Bases An acid is an electron-pair acceptor. F B F F H N H H + The third definition of acid/base is used in complexometric titrations A base is an electron-pair donor. F B F F H N H H acid base adduct H 2 O( l ) M(H 2 O) 4 2+ ( aq ) M 2+ adduct
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Anal Chem 251 Lect 9 Complexometric Titrations 7 Review - Coordination Compounds Metal ions (Lewis acids) form complexes or coordination compounds with neutral or charged electron pair donors (Lewis bases are also called ligands). The ligands of complex ions are molecules or anions with one or more donor atoms that each donate a lone pair of electrons to the metal ion to form a covalent bond.
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Anal Chem 251 Lect 9 Complexometric Titrations 8 Review Structures of Complex Ions: Coordination Numbers, Geometries, and Ligands Coordination Number - the number of ligand atoms that are bonded directly to the central metal ion. The coordination number is specific for a given metal ion in a particular oxidation state and compound. Geometry
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Lecture 8 - Lecture 9 Complexometric Titrations Chapter 13:...

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