2. Acidity Ability of a fluid to neutralize strong base. Measured by titration to pH ~8.3. Expressed as meq base kg –1.

3. Task 1 — Water and Carbonate Acidity Double click on file “Acidity.rea”. Unreacted fluid on Basis pane. Reactant pane sets up NaOH titration. Go to Results pane; render results with Gtplot. What is Ac? Due to H + ? Dissolved carbonate?

4. 0.511.522.53 4 5 6 7 8 9 10 NaOH reacted (mmoles) Water and Carbonate Acidity pH = 8.3 endpoint Ac = 2.1 meq kg –1 pH

5. Water and Carbonate Acidity 0.511.522.53 0.5 1 1.5 2 NaOH reacted (mmoles) Species Conc. (mmoles kg −1 ) H+H+ OH − CO 2 (aq)HCO 3 − CO 3 −− CaCO 3

6. 0.511.522.53 1e–5 1e–4.001.01.1 NaOH reacted (mmoles) CO 2 (g) fugacity Water and Carbonate Acidity

7. 0.511.522.53 0 1 2 3 NaOH reacted (mmoles) Carbonate alkalinity (meq acid kg −1 ) Water and Carbonate Acidity

8. Water Acidity Carbonate Acidity

9. mmol kg –1 meq kg –1 H+H+ 0.1 CO 2 (aq) 2.0 Acidity2.1

10. Task 2 — Mineral Acidity Add alumina to initial fluid. How does Ac change? How much Ac is from Al 3+ ?

11. pH = 8.3 endpoint Ac = 10.1 meq kg –1 Mineral Acidity 024681012 4 5 6 7 8 9 10 11 NaOH reacted (mmoles) pH

12. 024681012 0 1 2 - NaOH reacted (mmoles) Species Conc. (mmoles kg −1 ) CO 2 (aq) HCO 3 − CO 3 −− Al +++ Al(OH) 3 AlOH ++ Al(OH) 2 + Al(OH) 4 − Al 13 O 4 (OH) 24 (7+) H+H+ CaCO 3 OH − Mineral Acidity

13. Water Acidity Carbonate Acidity Mineral Acidity* *If no minerals or colloids form

14. mmol kg –1 meq kg –1 H+H+ 0.1 CO 2 (aq) 2.0 Al 3+ 4 × 2.0 8.0 Acidity10.1

15. Alkalinity Ability of a fluid to neutralize strong acid. Measured by titration to pH ~4.5. Expressed as meq acid kg –1, or as equivalent mg of CaCO 3. To convert, 1 meq acid = 50.05 mg CaCO 3.

16. Task 3 — Water and Carbonate Alkalinity Double click on “Alkalinity.rea”. Initial fluid at pH 11. Titrate HCl. What reactions give rise to alkalinity?

17. pH = 4.5 endpoint Alk = 5 meq kg –1 0123456 3 4 5 6 7 8 9 10 11 HCl reacted (mmoles) pH

18. 0123456 0 1 2 HCl HCl reacted (mmoles) Species Conc. (mmoles kg −1 ) H+H+ OH − CO 2 (aq) HCO 3 − CO 3 −−

19. Water Alkalinity Carbonate Alkalinity

20. mmol kg –1 meq kg –1 OH – 1.1 CO 3 2– 2 × 2.0 4.0 Alkalinity5.1

21. 0123456 0 1 2 3 4 HCl reacted (mmoles) Carbonate alkalinity (meq acid kg −1 )

22. 0123456 1e–7 1e–6 1e–5 1e–4.001.01.1 HCl reacted (mmoles) CO 2 (g) fugacity

23. Craig M. Bethke and Brian Farrell © Copyright 2016 Aqueous Solutions LLC. This document may be reproduced and modified freely to support any licensed use of The Geochemist’s Workbench® software, provided that any derived materials acknowledge original authorship.