[xshadow]

Hi!! ...I  don't understand a thing about the  approximated formula of the general equation of a strong acid/strong base tritation.


The general expression is:

[H⁺]- Kw/[H⁺] = C⁰D * (1-φ) =  C⁰ * (C/C+φC⁰) * (1-φ)

Where D= (C/C+φC⁰) is the diluition factor , C the concentration of the titrant while C⁰ the titrand one
Now my textbook says that sometimes I can approximate this expression assuming that D≈1 (for all φ values)

Now my question is WHEN I can do this assumption (??). My textbook says when the titrand concentration , C⁰, is much more concentrated than the titrant one...But in terms of number what does it means?

How much order of magnitude  the difference between (C_0 and C) must be??
Thanks a lot,and sorry for my bad english.

[Borek]

Have you heard about 5% rule?

http://www.chembuddy.com/?left=pH-calculation&right=general-pH-calculation

[xshadow]

Have you heard about 5% rule?

http://www.chembuddy.com/?left=pH-calculation&right=general-pH-calculation

mmhh...
Usually when I calculate pH of an acid I know ,for example ,that I can made some approximation [H⁺] =  Ka/[H⁺] + Ka

And I can use the approximated  formula if [H⁺] >> Ka 
And ">>" is equal to say  that  [H⁺]  ≥10²Ka   or [H⁺] ≥ 20/40 Ka  (much approximation error I think)


But ...for a tritation is the same??
My textbook only says that in a titration the  error must be lower than 0,1%.
SO what does it means this when I have to estimate if the DILUITION FACTOR D of a tritation is negligible or not

 D= (C/C+φC⁰)
how much C> φC⁰ must be in order to get D≈1

Thanks.

[Borek]

Titration error and pH calculation error are two different things, don't mistake stoichiometry for the equilibrium.

[xshadow]

Titration error and pH calculation error are two different things, don't mistake stoichiometry for the equilibrium.

so for diluition factor (that appears in the  titolation curve  expression )  to say that D≈1= ??

I need that C > 20/40 C⁰  ?

Is correct?
I have only to understand this...