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Scatter Diagram data for activity plots


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I am wondering why I can plot scatter data onto an activity diagram (ac2 plot) of log [K+]/[H+] vs. log [siO2(aq)], where [ ] indicates activity, but when I try to plot a similar diagram for log [Ca++]/[H+]^2 vs. log [siO2(aq)], I get the following error


"scat: Can't plot scatter data; doesn't contain: log ratio Ca++/H+^2".



The scatter data "scripts" that I have been using are the follows:


# Act2 scatter data for activity diagram
"SiO2(aq)" "K+/H+"
-4.5052 5.8563 blue blot
-3.4015 4.0147 green triangle
-3.3841 4.3142 red blot
-3.3813 4.6157 red triangle
-3.4283 4.0639 red square
-3.3579 4.5173 green square
# Act2 scatter data for activity diagram
"SiO2(aq)" "Ca++/(H+)^2"
-4.5052 12.924 blue blot
-3.4015 10.2125 green triangle
-3.3841 10.6879 red blot
-3.3813 11.3482 red triangle
-3.4283 9.8096 red square
-3.3579 11.6956 green square



Again, the one for potassium works fine, but the one for calcium is right out.




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Hi Karen,


I'm looking into why this isn't working correctly. FYI, Act2 will correctly read scatter data from a GSS spreadsheet or text file with activity values and calculate the appropriate ratios, but it's not reading certain activity ratios directly. So if you have analyses for one or more water samples in GSS, go to +analyte -> Calculate... -> Variable type: species activities -> Ca++, H+, K+, SiO2(aq) and the program will add entries for the activity of the selected species. Save the gss spreadsheet, then drag the gss file onto your Act2 window (or go to File -> Open -> Scatter Data and browse to the file.


If you'd like to use the text files, just include separate columns for Ca++ and H+ instead of the ratio Ca++/H+^2. You'll enter the activity values as logarithms, as you did for SiO2(aq).


Hope this gets you back up and running quickly. Again, we'll look into why values for ratios themselves aren't working properly.



Brian Farrell

Aqueous Solutions

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Hi Brian,

Thanks for your reply. I followed your advice and it worked. So, in case anyone else reads this, the modified scatter data for the case of Mg++ that works is:


# Act2 scatter data for activity diagram
"SiO2(aq)" "Mg++" "H+"
-4.5052 -1.9982 -8.03 blue blot
-3.4015 -2.638 -6.9 green triangle
-3.3841 -2.5328 -7.15 red blot
-3.3813 -2.74 -7.55 red triangle
-3.4283 -2.6321 -6.76 red square
-3.3579 -2.8465 -7.7 green square
Best wishes,
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  • 2 weeks later...

Hi Karen,


GWB 10.0.5 is now available. The update includes a fix to the problem you encountered with reading activity ratios from scatter data files. You can now specify the activity of the numerator and denominator species separately (i.e. Ca++, H+), or you can specify the activity ratio directly. In the latter case, you would use the label Ca++/H+^2, with no parentheses, for the diagram axis you described.




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