## roselin Group Title what does the following mean? Calculate single ion activity coefficients for Cs^+, Cd^2+,Al^3+ and dissolved H2CO3 as a function of ionic strength for 10^-4 lessthan equal I lessthan equal to1? one year ago one year ago

1. aaronq

they want the activity coefficients for the different ions considering the ionic strength given

2. roselin

so from 10^-4 to 1?

3. roselin

i am using the davies equation to calculate it, so each time I have to change the ionic strength th?

4. aaronq

hm no that doesn't seem right. i don't know what they mean by $$10^{-4} \leq 1$$, it doesn't make sense.

5. roselin

its $10^{-4}\le I \le1$

6. aaronq

oh, i thought you typed the same thing twice accidentally. I guess they want it within that range? thats a large range though. I would graph it

7. aaronq

on excel of course

8. roselin

we have to calculate and plot it

9. aaronq

i guess do a few points for each ion and then plot it

10. roselin

can I show you the full question ? please tell me what I should do

11. aaronq

plug it into the formula? $$log\;\gamma=0.5Z^+_0Z^-_0.. etc$$ it's kinda weird though because they don't give you the negative counter ion

12. roselin

if I were to do this manually using that given range, how would I approach it?

13. aaronq

you would calculate the coefficient for several points (ionic strengths) do 3 or 4, then plot these. Activity coefficient on the y axis and ionic strength on the x axis (although you can do on which every way you want)

14. aaronq

it's much easier if you do it in excel though

15. roselin

yes, that is where I am having problem.

16. roselin

like that range is between 10^-4 to 1 right?

17. aaronq

yep thats the range of "I" they gave

18. roselin

how would I calculte that in excel though?

19. roselin

if I do it manually then can I chose to do something like I= 10^-4,10^-3, 10^-2 and 10^-1?

20. roselin

choose**

21. aaronq

yeah thats fine

22. aaronq

for excel you need the x data point and the y data point the x you can just make up: 10^4, 10^3 then for the y you have to use the result from the equation, so you would type up the equation and use the x data points, then fill it. If you're not familiar with excel trying it this way might take you awhile

23. roselin

okay, thank you so much.

24. aaronq

no problem, good luck!

25. roselin

thanks :-)