Chemistry Please confirm my Activity Coefficient Calculations

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SUMMARY

The forum discussion centers on the correct calculation of the ionic strength (I) and activity coefficients (γ) for electrolyte solutions, specifically KNO3 and CaSO4. The correct formula for ionic strength is I = 1/2∑cz², where c represents the concentration of each ion. The user initially misapplied the formula by using √I instead of I, leading to incorrect results. After recalculating with I = 0.0666 M, the user achieved an overall value of 0.41, aligning closely with experimental data.

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  • Review the derivation of the ionic strength formula I = 1/2∑cz²
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Yokoko
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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.
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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.)
 
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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No! 1/2Σcz2 is I, not √I, as I said before. (What are the units?) I = 0.0666M.
 
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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