How to convert mg/L to activity?

[Anna]

Hi, I am using the ACT2 app to create a predominance diagram with lead and carbonate. I would like to fix the dissolved inorganic carbon in the system. My DIC is 5 mg/L. Could anyone help me convert that to "activity?" Thanks!

[Jia Wang]

Hello,

There are a couple of options for this. In some dilute fluids, you may assume that the activity coefficient is close to 1 and the molal concentration roughly the same as the activity. 

If you have a fluid analysis, you can also use SpecE8 to calculate the distribution of mass amongst species. SpecE8 will also report the activity for each species which can be used to set up your Activity diagram.

For more information on using SpecE8, refer to section 7 in the GWB Essentials User Guide. 

Hope this helps,
Jia Wang
Aqueous Solutions LLC