Please confirm my Activity Coefficient Calculations

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Discussion Overview

The discussion revolves around the calculations of the activity coefficient, specifically focusing on the correct computation of the ionic strength (I) and its implications for determining the activity coefficient (γ) in the context of solutions containing KNO3 and CaSO4. The scope includes mathematical reasoning and technical clarification of the formulas involved.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant asserts that the correct formula for ionic strength (I) is I = 1/2∑cz2 for all ions present, challenging the use of √I in calculations.
  • Another participant expresses uncertainty about the calculations, initially assuming that s (the concentration of simple ions) is equal to c, and later revising their approach to calculate I correctly.
  • A participant confirms the calculation of I as 0.0666M, suggesting that this value leads to an overall activity coefficient that aligns with experimental values.
  • There is a correction regarding the interpretation of the ionic strength formula, emphasizing the importance of using I rather than √I.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the initial calculations, but there is agreement on the correct interpretation of the ionic strength formula after some clarification. Disagreement exists regarding the initial assumptions and calculations made by one participant.

Contextual Notes

There are unresolved questions about the units used in the calculations and the assumptions regarding the concentrations of the ions involved. The discussion reflects a dependency on the definitions of terms and the correct application of formulas.

Yokoko
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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
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IMG_20201025_192654__01.jpg
 
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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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