Modeling pH in Natural Waters©
Morten Sielemann
Environmental Engineering Laboratory
Aalborg Univeristy
Aalborg DK-9000
mail to: Mortensielemann@mail1.stofanet.dk

Niels Peder Raj Andersen
Environmental Engineering Laboratory
Aalborg Univeristy
Aalborg DK-9000
mail to: i5np@civil.auc.dk

Kristian Keiding
Environmental Engineering Laboratory
Aalborg Univeristy
Aalborg DK-9000
mail to: i5kk@civil.auc.dk

Modelling chemical systems is a valuable way of learning and verifying obtained knowledge through measured data. In this Mathcad document, the chemical system is a river, where several known and unknown chemical processes take place. Modelling the pH variation in rivers is an interesting exercise, not only from an environmental point of view, but also because it makes use of basic physical, chemical, biological and numerical principles obtained through undergraduate courses.

To employ this document, no special knowledge of Mathcad is required. Small exercises placed in the document will show the student how to solve equilibrium problems with the simultaneous equation solver and differential equations by an iterative matrix setup. Additional help can easily be found in the Mathcad menu.

The pH model is built systematically using theory and logical assumptions to include or exclude different parameters and processes. After that, a short discussion will show how the initialisation values were found.

The final model will show how equilibrium problems can be solved in discreet steps for a dynamic system using the simple assumption, that equilibrium reactions are much faster than transport phenomena and biological transformation. Furthermore, the model will be used to predict the behaviour of pH when changing temperature, ionic strength, buffer capacity and biological transformation rates.

Users must supply the missing variables and constants while using the document.
Editor's Commentary
Audiences: Upper-Division Undergraduate
Pedagogies: Computer-Based Learning
Domains: Analytical Chemistry, Environmental Chemistry
Topics: Acids / Bases, Equilibrium, Kinetics, Mathematics / Symbolic Mathematics, pH, Water / Water Chemistry
File NameDescriptionSoftware TypeSoftware Version
pHModeling8.mcd JCE Mathcad 8 Computational Document Mathcad 8
pHModeling6.mcd JCE Mathcad 6 Computational Document Mathcad 6
pHModeling.pdf Read-Only Document (based on Mathcad 8 version)
JCE JCE Subscribers only: name and password or institutional IP number access required.
Sielemann, M.; Andersen, N. P. R.; Keiding, K. J. Chem. Educ. 2002, 79, 528.
Comments to: Morten Sielemann   Mortensielemann@mail1.stofanet.dk
Niels Peder Raj Andersen  i5np@civil.auc.dk
Kristian Keiding      i5kk@civil.auc.dk
©Copyright 2002 Journal of Chemical Education