Please confirm my Activity Coefficient Calculations

  • #1
Yokoko
15
1
Homework Statement:
I've had a go at these but am unsure about the result. I thought the values would have to be closer to each other.
Relevant Equations:
See picture
IMG_20201025_192654__01.jpg
 

Answers and Replies

  • #2
mjc123
Science Advisor
Homework Helper
1,285
689
You have not calculated I correctly. I (not √I) = 1/2∑cz2 for ALL ions present.
Then you haven't used your calculated value for I in the equation for logγ. You used c. Why?
(Do it correctly, and it does come out close to the experimental value.)
 
  • #3
Yokoko
15
1
IMG_20201026_110941.jpg

Thanks for your answer. Again, I'm not sure if I understood this correctly.

I used c as I thought s = c for simple ions. I now took the root of √I to get I.

I assumed the C for KNO3 = 0.0050 and C for CaSO4 = s = 0.0154

This might be where I am wrong?
 

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  • #4
mjc123
Science Advisor
Homework Helper
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No! 1/2Σcz2 is I, not √I, as I said before. (What are the units?) I = 0.0666M.
 
  • #5
Yokoko
15
1
Oops thanks, I misread your earlier message.
With I = 0.0666 I get an overall value of 0.41 which fits.

Thanks again!
 

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