CHE134 Summer Lecture 3

CHE134 Summer Lecture 3 - COMPLEXOMETRIC TITRATION OF...

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Click to edit Master subtitle style TITRATION OF CALCIUM COMPLEXOMETRIC CALCIUM
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OBJECTIVE: To determine the calcium content of an unknown substance by complexometric titration. CONCEPTS: End/Equivalence Point Ligands (complexers) Polydentate Ligands Complex Formation Stability of Complexes Selective Complexation Buffers for pH control TECHNIQUES: Weighing by Difference Titration EQUIPMENT: Buret
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Ca is the 5th most abundant element on Earth comprising 3.6% of the crust Its compounds are found virtually everywhere, in the form of minerals (like calcite and gypsum ) The element itself, however, was not isolated and identified until 1807, when Humphrey Davy isolated it by electrolysis of its molten chloride. and in the remains of living organisms (seashells, bones, etc.)
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TECHNIQUE Formation of Ca+2 complex with (EDTA) Ethylene Diamine E thylene D iamine T etra-acetic A cid C C H H H H C C H H H H N N CH 2 H 2 C CH 2 CH 2 C C HO O O OH C C HO O O OH H C C H H H H 2 N NH 2 Na di-sodium salt Na
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EFFECT OF pH Can write “EDTA” as: Na2H2EDTA which dissolves in neutral solutions to give H2EDTA 2- anions However, the most effective complexing form is EDTA 4- Therefore, to neutralize last two H+’s, we will maintain a moderately basic environment for the titration by adding a pH = 10 buffer
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Complex between EDTA and Ca+2 is 1 : 1 i.e., 1 EDTA4- REACTS WITH 1 Ca+2 EQUIVALENCE (END) POINT = when all Ca+2 has reacted with EDTA But, neither EDTA4-, nor its COMPLEX with Ca+2 IS COLORED How will we know when EQUIVALENCE (End) POINT has been reached? O O O O Ca O N O N O
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USE INDICATOR ERIOCHROME BLACK T ( EBT ) - a BLUE dye Like EDTA, EBT also forms a 1 : 1 complex with Ca+2 The complex is RED , BUT Ca-EDTA complex is MUCH MORE STABLE than
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This note was uploaded on 01/09/2011 for the course CHE 134 taught by Professor Staff during the Summer '08 term at SUNY Stony Brook.

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CHE134 Summer Lecture 3 - COMPLEXOMETRIC TITRATION OF...

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