Charge Balance Changing when Eh added to GSS

[shensel]

Hello,

I noticed that my charge imbalance error changes substantially when I add Eh to my sample data in GSS (changing the actual Eh value does not seem to have a strong effect, just the actual act of adding the analyte). With Eh (500 mV) it calculates -14.82%, and without it calculates -2.283. Given the formula for charge imbalance error calculation, why does the Eh affect the result? I've a ttached my GSS file here.

 

Thanks,

Scott

CB Test.gss

[Jia Wang]

Hello Scott,

Thank you for attaching your GSS file. When you add an analyte such as O2(aq) or Eh, it is used to set the oxidation state of your system, which can very much affect the speciation calculation and consequently the charge imbalance. I think you can see this best if you launch your sample in SpecE8 and calculate speciation with and without Eh. You can see with an Eh constraint, the program assumes redox equilibria and distributes mass across oxidation dates accordingly. You can prevent the program from doing this for any or all couples by going to "Config" -> "Redox couples" dialog. In GSS, you can disable redox couples by going to the same dialog under the "Data" tab.

Please see more information about redox coupling in section 2.4 of the GWB Essentials guide.

Hope this helps,
Jia Wang
Aqueous Solutions LLC

[shensel]

Thank you Jia, that makes sense.

[Jia Wang]

You're welcome Scott. I hope the rest of your project goes smoothly.

Best regards,
Jia