[borodin]

Hi!

I have two questions:

1st - For a project i need to calculate the limiting molar condutivity of CTAB (surfactant) but i have some problems here.  Base on Kohlrausch's law, i ploted the square of Concentration Vs Molar condutivity and i've got this:



Λ=Λ⁰ − K√C

So, in practice is just make an extrapolation and check where the line crosses the y-axis. But the reference number of Λ⁰ that i have is 98 and here the number is very higher that. What points would i consider to make the extrapolation?

Maybe temperature affect this value? (this data is at 35ºC and referenceof 98 is @25ºC) Here http://www.geo.tu-freiberg.de/hydro/vorl_portal/statistik/Coury1.pdf they say:

"This parameter represents the molar conductivity for a compound that would hypothetically be measured in the limit of infinite dilution (i.e., the y-axis intercepts of plots like those in F1). In practice, such values are obtained by fitting experimental data to an equation known as Kohlrausch’s Law"

And in page 93 of this document in Examples of Use of Tabulated Values section you see that is quite diferent the extrapolation from the theorical data. Making the extrapolation of the KCl of Acetic acid don't give near the real condutivity at this. How much science is in that?


2nd - I'm working in molality (because i'm working at differents temparatures, avoiding this way problems associated with the effect of temperature over volume). But, i need to use limiting molal ionic  condutivity. Is there a reference for this data? Or an expression to convert this molarity data to molality?

Thank you very much!