why NH3.NH4CL buffer solution added during determination of hardness of water by EDTA method?
Answers
Answer:
When determining the hardness of water an indicator dye is used which gives either a pink color to the solution when Mg2+ and Ca2+ are still present, or a blue color when all of the metal ions have reacted with the EDTA4-.
As far as I know the pH needs to be at least 10 for the EDTA to let go of its H+ ions so we get the EDTA4- solution we need for the reaction with Mg2+ and Ca2+.
The reaction [EDTA --> EDTA4- + 4H+] by itself will change the pH of the total solution (it's releasing H+ ions, after all) and we're constantly adding EDTA-solution until the solution is blue and all hints of pink have gone. For this reason we need a buffer which will keep the total solution at pH10 even if we have to add considerable amounts of EDTA.
Explanation:
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Answer:
When determining the hardness of water an indicator dye is used which gives either a pink color to the solution when Mg2+ and Ca2+ are still present, or a blue color when all of the metal ions have reacted with the EDTA4-.
As far as I know the pH needs to be at least 10 for the EDTA to let go of its H+ ions so we get the EDTA4- solution we need for the reaction with Mg2+ and Ca2+.
The reaction [EDTA --> EDTA4- + 4H+] by itself will change the pH of the total solution (it's releasing H+ ions, after all) and we're constantly adding EDTA-solution until the solution is blue and all hints of pink have gone. For this reason we need a buffer which will keep the total solution at pH10 even if we have to add considerable amounts of EDTA.
Explanation:
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