What Should Be Noticed When Titrate Disodium EDTA Standard Solution?
Disodium EDTA dihydrat is used as an anticoagulant in blood collection tubes. It is a white powder needs to be configured into a solution before used. The standard solution needs to be titrated. Two indicators should be used for calibration, because in complexometric titration, the acidity range of EDTA with different metal ions to form different stable complexes. Eliminate base effects to reduce errors.
When configuring disodium EDTA titration,the following points need to be paid attention:
1. Phenolphthalein cannot be used to replace methyl red when neutralizing HCL in the standard.
Ammonia neutralizes hydrochloric acid, the product NH4cl is a strong acid and weak base salt,the PH is acidity, while phenolphthalein is an alkaline indicator, so it cannot be used as an indicator,and the discoloration range of methyl red is 4.4-6.2, so it can be used as an indicator.
2. Mg2+-EDTA can improve endpoint acuity
Mordant Black can form a stable complex with Mg2+, and the hromogenic is very sensitive, but the complex formed with Ca2+ is unstable and has low color sensitivity. Therefore, when Ca2+ is titrated with EDRA in a pH=10 solution, a small amount of MgY is first added to the solution to make displacement reaction to replace Mg2+.
3. The titration must be carried out in a buffer solution
In the process of complexometric titration,H+ is continuously released with the formation of complexes, so the acidity of the solution continues to increase.And reducing the stability of the complexes and destroys the optimum acidity range of the indicator discoloration, resulting in a large error. Therefore, in complexometric titration, it is necessary to add a buffer solution to control the PH of the solvent.
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