the experiment about(Hardness of water by EDPA titration)
Q1.Why are two indicators used in the experiment?
(the indicator: Erichrome Black T and hydroxynaphthol
The second titration is about determination of concentration of Ca2+ and hydroxynaphthol is used for the second titration,the first titration is about determination of total hardness(Mg2+ and Ca2+)
chem一問
2007-12-01 1:19 am
回答 (2)
2007-12-01 11:06 pm
✔ 最佳答案
Eriochrome Black T indicator does not give a satisfactory color change at high pH. Hydroxy naphthol indicator is similar to Eriochrome Black T, and functions in the same manner, but at high pH.Procedure for Calcium Only. If the pH of the sample solution is raised to about 13, magnesium will precipitate as the very insoluble hydroxide which will not react with EDTA, and calcium alone can be titrated using calcon indicator. Since the total hardness titration gives the sum of both Ca and Mg in the sample, and titration at pH 13 gives Ca only, Mg can be obtained by difference.
I hope this can help with your understanding. =)
參考: My knowledge
2007-12-02 1:54 am
E D T A
收錄日期: 2021-04-13 14:36:45
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20071130000051KK01872