Complexometric Titration, EDTA Titration

The pptx on complexometric titrations, EDTA titration, Why EDTA is used in complexometric titration, Classification of EDTA titration, EDTA titration curve etc.

1. Course :Analytical Chemistry Course Code: ACCE 2201 07.03.2018 Presentation on EDTA TOPICS : What is EDTA? Structure of EDTA. EDTA in analytical chemistry. Complex titration with EDTA. Classification of EDTA titration. EDTA titration curve. Effect of pH on EDTA equilibria. Application of EDTA PRESENTED BY ASIF PAPPU

2. EDTA: Six binding sites 4 H on carboxylic acid groups (H’s are removed, so –COO-) 2 lone pairs of electrons on nitrogens The most common complexometic titrant. Normally used like as a salt . Structure of EDTA EDTA is ethylenediaminetetraacetic aicd

3. EDTA in analytical chemistry In analytical chemistry EDTA is used for complexometic titration . It is a primary standard. It is a chelative agent. Forms 1:1 complexes with majority of metals. EDTA is a hexaprotic system (H 6 Y 2+ ) with 4 carboxylic acids and 2 ammoniums. Complexometic titration : A titration based on complex formation is called complexometic titration

4. Complex titration with EDTA: EDTA, ethylenediaminetetraacetic acid, has four carboxyl groups and two amine groups that can act as electron pair donors, or Lewis bases. The ability of EDTA to potentially donate its six lone pairs of electrons for the formation of coordinate covalent bonds to metal cations makes EDTA a hexadentate ligand. However, in practice EDTA is usually only partially ionized, and thus forms fewer than six coordinate covalent bonds with metal cations. EDTA forms an octahedral complex with most 2+ metal cations, M2+, in aqueous solution. The main reason that EDTA is used so extensively in the standardization of metal cation solutions is that the formation constant for most metal cation-EDTA complexes is very high, meaning that the equilibrium for the reaction: M2+ + H4Y → MH2Y + 2H lies far to the right. Carrying out the reaction in a basic buffer solution removes H+ as it is formed, which also favors the formation of the EDTA-metal cation complex reaction product. For most purposes it can be considered that the formation of the metal cation EDTA complex goes to completion, and this is chiefly why EDTA is use.

5. Classification of EDTA Titration Direct Titration analyte is titrated with standard EDTA analyte is buffered to an appropriate pH at which the conditional formation constant for the metal-EDTA complex is large and the color of the free indicator is distinctly different from that of the metal-indicator complex Back titration a known excess of EDTA is added to the analyte the excess EDTA is titrated with a standard solution of a second metal this method is useful if analyte precipitates in the absence of EDTA - the analyte reacts too slowly with EDTA under titration conditions - analyte blocks the indicator -metal used in back titration must not displace the analyte metal ion from its EDTA complex

6. Classification of EDTA titration Replacement titration Method is useful is the metal ions do not react with metal indicator analyte is treated with excess Mg(EDTA) 2- to displace Mg 2+ M n + + MgY 2- MY n-4 + Mg 2+ the displaced Mg 2+ is titrated with standard EDTA Example : 2Ag + + Ni(CN) 4 2- 2Ag(CN) 2 - + Ni 2+ ( iv) Alkalimetric titration A solution of Na 2 (EDTA) is added to a solution containing metallic ions, complexes are formed with the liberation of two equivalents of hydrogen ion. Hydrogen ion is titrated with a standard solution of sodium hydroxide using an acid base indicator.

7. Curves of EDTA titration Fig. 12-10 EDTA titration illustrated for reaction of 50.0 mL of 0.0500 M Mn + with 0 0500 M EDTA with 0.0500 M EDTA. K’f = 1.15 x 10 16 The concentration of free Mn + decreases as the titration proceeds. Mn + + EDTA MYn-4 Region 1: Before the Equivalence Point - There is excess Mn + left solution after the EDTA has been consumed. - The concentration of free metal ion is equal to the concentration of excess, untreated Mn + untreated M . - The dissociation of MYn-4 is negligible. Mn + + EDTA ֖ MYn-4 Region 3 Excess EDTA

8. Curves of EDTA titration Region 2 : At the Equivalence Point There is exactly as much EDTA as metal in the solution There is exactly as much EDTA as metal in the solution. We can treat the solution as if it had made by dissolving pure MYn-4. Some free Mn + is generated by the slight dissociation of MYn-4 - Some free M : n+ is generated by the slight dissociation of MYn 4: MYn-4 ֖ Mn + + EDTA EDTA f h l i EDTA refers to the total concentration of free EDTA in all of its forms. At the equivalence point, [ Mn +] = [EDTA] Region 3 Excess EDTA

9. Curves of EDTA titration Region 3 : After the Equivalence Point There is excess EDTA and virtually all the metal ion is in the form MY There n-4 is excess EDTA, and virtually all the metal ion is in the form MY . The concentration of free EDTA can be equated to the concentration of excess EDTA added after the equivalence point EDTA added after the equivalence point . Free metal concentration is calculated EDTA MYn 4 Region 3 Excess EDTA

10. Effect of on EDTA titration Consider the formation of the EDTA chetate of a Ca2+. This can be represented by Ca 2+ + Y 4- = CaY 2- The equation is shifted to the left as the hydrogen ion concentration is increased, due to competition for the chealting anion by the hydrogen ion. The formation constent K f = [CaY 2- ]/[Ca 2+ ][Y 4- ] The overall reaction is Ca 2+ +H4 Y D CaY 2- + 4H + According to Le chatelier’s low , increasing the acidity ,will favor the competing fquilibrium that is proportion of Y 4- Decreasing the acidity will favor formation of the CaY 2- chelate.

11. Applications of EDTA: 1.EDTA titrations are routinely used to determine water hardness in lab. In this reaction, the EDTA ligand will react with the minerals present in the water (mainly calcium and magnesium carbonates, sulfates, etc .) 2. Food industry EDTA is used as a stabilizing agent in the food industry EDTA deactivates enzymes ( that contain metal) responsible for food spoilage by removing the metal ions from them and forming stable chelates with them. 3 . Medical As an anticoagulant for stored blood in blood banks; it prevents coagulant by sequestering the calcium ions required for clotting. As an antidote for lead poisoning, calcium disodium EDTA exchanges its chelated calcium for lead, and the resulting lead chelate is rapidly excreted in the urine.

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