[kiloa]

hello everyone ,

i'm trying standardization of 0.1N HCL with TRIS by using PH meter instead of indicator
what should i do to use ph meter for standardization ?

[chenbeier]

You need the pH where normally the indicator change his colour. If you know this then you can measure it with pH-Meter.

[kiloa]

but the color of indicator change  when the excess of titrant present ...that mean the end point is passed !!

[chenbeier]

What is the problem.

Please describe how you standardize if you use the indicator. What is the procedure?

[kiloa]

i don't want to use indicator because Two people might see a different shade of color.
and how can i measure concentration of  solution by titration with ph meter ?
my procedure if i use indicator as the following :
1- i usually preferred using salt as primary standard
2- i weigh amount of salt according to theoretical concentration of solution that i want to standardize it
3- put the suitable indicator
4- make titration till color change

[Borek]

You need to record the curve using pH meter and detect the end point from the curve shape. Either look for the steepest curve part, or find where the derivative dpH/dV has maximum value.

[kiloa]

can you clarify to me with example ?
for example i want to standardize hcl solution vs tris buffer salt >>>what should i do after taking suitable amount of salt and dissolve it ?

[chenbeier]

So you want to prepare a standard of  Tris and not prepare a standard of HCl?

You dissolve a certain amount of the salt in a known volume of water. Then immerse the pH probe and start titration in small steps like 0,1 ml by using HCl and record the pH and draw  a curve

[kiloa]

yes, at this point (draw the curve) all things are okay but i don't know how can i finding equivalence point from the curve ?
or the actual volume that compensate it in equation to find actual concentration of HCL ?

[chenbeier]

Did you draw the curve? How does it looks like.?  Normally it should look like a big S. At the turning point of the curve is the equivalence point. And again what I said above add also indicator for comparison to get a feeling when you reach the point. Later for other titrations you dont need the indicator.