A2 Chemistry
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I am slightly confused; Will boiling remove the Mg2+ and Ca2+ ions from standard solutions of Mg2+ and Ca2+?
Also, I was wondering what the difference is between Calcon indicator and Patton and Reeder's indicator? Does one have a sharper end-point. Or are they both just as good when trying to find the concentration of Ca2+ using an EDTA titration?
270110
Corrie writes ....
If your standard solutions are made up using the sulphates or chlorides of calcium or magnesium then these solutions will behave as permanently hard water and not be softened by boiling.
Only temporarily hard water, containing the hydrogencarbonates of these metals, can be softened by boiling - as indicated in my earlier reply you.
According to Vogel's well-known textbook on Quantitative Inorganic Analysis Patton & Reeder's indicator can be used to titrate Ca2+ directly in the presence of Mg2+ at a pH between 12 - 14. The end-point is a sharp change from wine red to pure blue.
Calcon indicator can also be used to titrate Ca2+ in the presence of Mg2+ provided the pH is held at about 12.3 with a suitable buffer. Here the end-point change is from pink to blue.
It would seem either indicator would do - why not try both if they are available, and compare the results - more to add to your write-up?!
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updated: 27 January 2010
