Complexometric titrations are volumetric titrations, also known as chelatometry, in which the endpoint is indicated by a colored complex. In this type of titration, an indicator capable of producing a distinct color change throughout the titration is used to identify the endpoint of the titration.
The concentration of metal ions in a solution is determined using complexometric titrations. During titration, the volume of the analyte, titrant, and even the indicator is important. Complexometric titration utilizes indicators such as Eriochrome black T or calcein.
Which buffer solution is used in EDTA titration?
An ammonia buffer solution is used in EDTA titration. The complexometric titration is performed at a pH 10 in an NH4Cl + NH4OH buffer, which maintains the EDTA mostly in its half-neutralized form. In general, we use ammonium chloride and ammonia buffer in EDTA titrations to determine the hardness of the water.
Why buffer solution is used in EDTA titration?
A buffer solution is used in EDTA titration as it is resistant to pH changes. All reactions between metal ions and EDTA are pH-dependent. Changes in pH can cause metal ions and EDTA to react improperly.
Why is pH 10 buffer used in EDTA titration?
There are two reasons to maintain the pH 10 of the EDTA titration buffer. The first reason is that all reactions between EDTA and metal ions are pH-dependent, and for divalent ions, the solution should be kept basic for the reactions to proceed. The second reason is that for a suitable color change, the eriochrome black–T or solochrome black-T indicator requires a pH of between 8 and 10.
How do you prepare an ammonia buffer solution for hardness?
To prepare ammonia buffer solution for hardness, in a volumetric flask, dissolve 5.40 grams of ammonium chloride and 35.00 ml of a 10M ammonia solution in 100 ml of distilled water and properly mixed it.
Why control of pH is necessary for complexometric titration?
A buffer solution must be used to maintain a constant pH throughout a complexometric titration. Controlling the pH is necessary because the H+ ion plays an important role in chelation. Most ligands are basic and bind to H+ ions over a broad pH range.
During chelate formation, the metal often displaces a portion of these H+ ions from ligands (chelating agents). During chelate formation, the metal often displaces some of these H+ ions from the ligands.
What is the role of pH in EDTA titrations?
In buffer solution, the metal ions to be measured EDTA titrations are performed. The stability constant of the metal–EDTA complex is dependent on the pH used. For example, metals with a low stability constant require an alkaline pH. Low alkaline to mildly acidic pH is necessary for metals with high stability constant.
The dissociation reactions of acid from EDTA and H4Y are also pH-dependent. pH is also a crucial criterion for the proper operation of the indicator substance. Consequently, it is important to maintain the pH throughout the EDTA titration.
What happens if pH is not maintained in complexometric titrations?
A change in pH may lead to an improper reaction between the metal ion and EDTA. A buffer solution must be adequately maintained for EDTA titration because all reactions between metal ions and EDTA are pH-dependent.
Why is pH 10 buffer solution added during the determination of the hardness of water?
As in the determination of water hardness, indicator EBT is used, which requires a pH of 8–10 for color change. So the buffer solution is needed to preserve the pH of the solution.
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