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EDTA forms an octahedral complex with most 2+ metal cations, M, 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
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Second step is to measure absorbance (A’) of unknown solution and match it with the known absorbance-concentration plot of the standard solution. Thereby calculating the molar concentration of the unknown solution. This is calculated by using the formula, concentration of unknown =A’/(E*l). This can
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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
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capable of producing an unambiguous color change is usually used to detect the end-point of the titration. Complexometric titration are those reactions where a simple ion is transformed into a complex ion and the equivalence point is determined by using metal indicators or electrometrically.
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First step is to plot the absorbance(A) values of standard solution against molar concentrations (c) of the known solution. Then the best straight line is plotted, passing through the origin. The experimental points are plotted as per Beer’s law:
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in which the formation of a colored complex is used to indicate the end point of a titration. Complexometric titrations are particularly useful for the determination of a mixture of different metal ions in solution. An
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of several different complexes of the metal ion with the titrant, resulting in the presence of more than one complex in solution during the titration process.
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ligand. However, in practice EDTA is usually only partially ionized, and thus forms fewer than six coordinate covalent bonds with metal cations.
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Disodium EDTA is commonly used to standardize aqueous solutions of transition metal cations. Disodium EDTA (often written as
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In theory, any complexation reaction can be used as a volumetric technique provided that:
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To carry out metal cation titrations using EDTA, it is almost always necessary to use a
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A= E*c*l where E= molar extinction coefficient and l= optical path length usually 1 cm.
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this is chiefly why EDTA is used in titrations and standardizations of this type.
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to determine when the end point has been reached. Common indicators are organic
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capable of locating equivalence point with fair accuracy is available.
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designating the number of acidic protons bonded to the EDTA molecule.
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In practice, the use of EDTA as a titrant is well established.
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concentration of unknown/ concentration of known = A’/A.
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Interfering situations do not arise. For instance, the
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268:also be calculated using this given relation ,
256:Data processing and Calculation using Absorbance
192:groups that can act as electron pair donors, or
154:rapidly after each portion of titrant is added.
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109:Learn how and when to remove this message
16:Used to determine total hardness of water
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348:. Chemistry LibreTexts. 15 August 2021
142:Reactions for Complexometric titration
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47:adding citations to reliable sources
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182:ethylenediaminetetraacetic acid
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176:Complex titration with EDTA
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58:"Complexometric titration"
368:“ G.N Mukherjee. Page 30
366:Spectroscopic Estimations
342:"Complexation Titration"
281:complexometric indicator
166:complexometric indicator
122:Complexometric titration
150:The reaction reaches
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130:volumetric analysis
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350:. Retrieved
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36:verification
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352:13 December
198:hexadentate
194:Lewis bases
184:, has four
152:equilibrium
124:(sometimes
328:References
275:Indicators
235:reaction:
69:newspapers
381:Titration
317:Titration
135:indicator
375:Category
311:See also
305:Murexide
287:such as
186:carboxyl
83:scholar
247:Y + 2H
243:Y → MH
180:EDTA,
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303:, or
239:M + H
190:amine
90:JSTOR
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364:2. “
354:2023
285:dyes
62:news
219:4−x
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217:Na
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