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Zinc Titration with EDTA

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DeaZ96:
Hi,
I am trying to make zn titration of one solution which I know zn percentage. Sometimes I get the end point but the ml of Edta are less according to the  result I should get.
I am using so old xylenol orange. Can this be the problem?
If you have any suggestions please help me,to change something in the way I am doing it.


Titrant is EDTA. Indicator is Xylenol Orange.

Please help.

Borek:
What is the procedure you follow? Anything else in the solution?

DeaZ96:

--- Quote from: Borek on September 10, 2022, 05:43:21 AM ---What is the procedure you follow? Anything else in the solution?

--- End quote ---

My procedure is like this:
I use dried material(cu concentrate)in a 400 ml beaker. I add 10 ml HCl then 5 ml HNO3. When reaction finishes I add water in it and wait to dry,then 10 ml h2so4 1/1 for around 50 mins.After it,I add water and some drops of h2o2 and wait for boiling. I filtrate with blue filter.From the filtrated solution I take 100
Ml and  add 1 spoon of nh4cl and boil again. Then precipitate it with nh4 and filtrate with black filter. Afer i leave around one hour in hot plate solution is ready (i let it to be cold)
Before titration: i add hcl 1/1 till color becomes from blue to white
Again nh4 1/1 till solution becomes blue, then I add buffer( ph 5,5) and at the end two drops of xylenol orange.
I hope i was clear…

Borek:
Some parts are not clear: why the blue color before HCl addition? Things you do with HCl and ammonia (I suppose you mean NH3, not NH4+), followed by buffer addition are a bit strange as well - HCl/ammonia make a buffer with pH around 10, adding another buffer to lower pH back to 5.5 is surprising to say the least.

But first of all: I never saw such a procedure. The only method I ever used to determine Zn was titration with EDTA at pH 10 against eriochrome black T. While indicator choice is often secondary, pH of titration typically depends on the system and stability constants, so it is another surprising thing.

DeaZ96:

--- Quote from: Borek on September 11, 2022, 02:33:00 PM ---Some parts are not clear: why the blue color before HCl addition? Things you do with HCl and ammonia (I suppose you mean NH3, not NH4+), followed by buffer addition are a bit strange as well - HCl/ammonia make a buffer with pH around 10, adding another buffer to lower pH back to 5.5 is surprising to say the least.

But first of all: I never saw such a procedure. The only method I ever used to determine Zn was titration with EDTA at pH 10 against eriochrome black T. While indicator choice is often secondary, pH of titration typically depends on the system and stability constants, so it is another surprising thing.

--- End quote ---

Can I have your procedure please? But I have only xylenol orange,can it be used?

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