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Chemistry (including Biochemistry)/water ph and Ca2+ based water softening


Dear Dr. Robichaud,

For my household water, I have low pH and high hardness.  I have been advised by water treatment companies to purchase a pH neutralizer (calcite based) and a water softener.  One of these will add calcium to the water and the other will take it out.  How can this accomplish anything?  I would think a chemical feed system that adds soda ash would be a better compliment to a water softener.

Hi Mark!

Yup, you're right. It would just as much sense, if not more, to add soda ash.

Things I don't know about, which may be contributing factors in this decision...

1) How to automate the pH neutralizing process (Is it a unit or simply a tank of some kind?)
2) Is calcite cheaper than soda ash?
3) Does one method or the other generate more fallout? (Since Na in solution has one positive charge and Ca has two, it may be that you get half as much 'waste' from a calcium based system than a sodium one.)

What I *can* tell you is this.

Most water softeners are ion-exchanged Na and K for Ca and Mg.  When you dissolve CaCO3 at low pH (acid) you get:

CaCO3(s) + 2 H3O-(aq) ---> Ca2+  + H2CO3- + 2 H2O

In English that's 'Solid calcium carbonate dissolves in acid to form Calcium ions, Carbonic Acid, and Water'.

This isn't all that useful at first blush, because we're adding acid to acidic water! However...

H2CO3  <---> H2O + CO2(g) (This reaction is at equilibrium, meaning it can go either way.)

The carbonic acid then goes on to bubble out of solution as carbon dioxide, leaving neutral water behind. (We use this property of H2CO3 to maintain blood pH as well.)

Now Ca(OH)2 is not soluble at higher pH - it bombs out of solution. Bubble out enough CO2 and the pH goes up (more OH-). The presence of other ions in solution actually encourages Ca(OH)2 to crystallize more. Win-win.

Ca2+ + 2 OH- ---> Ca(OH)2 (s)

So, by using calcium (calcite) we've actually removed Ca(OH)2 from your water. Calcium out BEFORE adding it to the water softener unit. This improves the lifetime of your resin, since you are only removing Mg2+ from your water and replacing it with Na and K. It does mean you'll have to clean scale (Ca(OH)2) out of your water tank periodically with vinegar. :)

Please let me know if that makes sense!

Chemistry (including Biochemistry)

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Trista Robichaud, PhD


No homework questions, especially ones copied and pasted from textbooks. I will answer questions about principles or give hints, but I do not do other's homework. I'm comfortable answering basic biochemistry, chemistry, and biology questions up to and including an undergraduate level of understanding. This includes molecular biology, protein purification, and genetics. My training/inclination is primarily in structural biology, or how the shapes of things affect their function. Other interests include protein design, protein engineering, enzyme kinetics, and metabolic diseases such as cancer, atherosclerosis, and diabetes. My chemistry weaknesses are that I do not know organic or inorganic synthesis well, nor am I familiar with advanced inorganic reactions. I will attempt quantum mechanics and thermodynamics questions, but primarily as they relate to biological systems. Furthermore, I cannot tell you if a skin photograph is cancerous, or otherwise diagnose any disease. I can tell you how we currently understand the basic science behind a disease state, but I cannot recommend treatment in any way. Please direct such questions to your medical professional.


I hold a PhD in Biomedical Science from the University of Massachusetts Medical School in Worcester. I specialize in Biochemistry, with a focus on protein chemistry. My thesis work involved the structure and functions of the human glucose transporter 1. (hGLUT1) Currently I am a postdoc working in peptide (mini-protein) design and enzymology at the University of Texas Health Science Center in San Antonio, Texas. I am in Bjorn Steffensen's lab (PhD, DDS), studying gelatinase A and oral carcinoma.

2001 American Association for the Advancement of Science
2007 American Chemical Society
2007 Protein Society
2011 UTHSCSA Women’s Faculty Association

Levine KB, Robichaud TK, Hamill S, Sultzman LA, Carruthers A. Properties of the human erythrocyte glucose transport protein are determined by cellular context. Biochemistry 44(15):5606-16, 2005. (PMID 15823019)
Robichaud TK, Appleyard AN, Herbert RB, Henderson PJ, Carruthers A “Determinants of ligand binding affinity and cooperativity at the GLUT1 endofacial site” Biochemistry 50(15):3137-48, 2011. (PMID 21384913)
Xu X, Mikhailova M, Chen Z, Pal S, Robichaud TK, Lafer EM, Baber S, Steffensen B. “Peptide from the C-terminal domain of tissue inhibitor of matrix metalloproteinases-2 (TIMP-2) inhibits membrane activation of matrix metalloproteinase-2 (MMP-2)” Matrix Biol. 2011 Sep;30(7-8):404-12. (PMID: 21839835)
Robichaud TK, Steffensen B, Fields GB. Exosite interactions impact matrix metalloproteinase collagen specificities. J Biol Chem. 2011 Oct 28;286(43):37535-42 (PMID: 21896477)

Poster Abstracts:
Robichaud TK, Carruthers. A "Mutagenesis of the Human type 1 glucose transporter exit site: A functional study." ACS 234th Meeting, Boston MA. Division of Biological Chemistry, 2007
Robichaud TK, Bhowmick M, Tokmina-Roszyk D, Fields GB “Synthesis and Analysis of MT1-MMP Peptide Inhibitors” Biological Chemistry Division of the Protein Society Meeting, San Diego CA 2010
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Catalytic Domain Exosites Contribute to Determining Matrix Metalloproteinase Triple Helical Collagen Specificities” Dental Science Symposium. UTHSCSA 2011
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Exosite Interactions Determine Matrix Metalloproteinase Specificities” Gordon Research Conference on Matrix Metalloproteinase Biology, Bristol RI 2011

Oakland University, Auburn Hills MI BS, Biochemistry 1998
University of Massachusetts Medical School, Worcester MA PhD, Biochemistry & Molecular Pharmacology 2001-2008
University of Texas Health Science Center, San Antonio TX Postdoc, Biochemistry 2009-Present

Awards and Honors
1998 Honors College Graduate, Oakland University
2009 Institutional National Research Service Award, Pathobiology of Occlusive Vascular Disease T32 HL07446
2011 1st Place, Best Postdoctoral Poster, Dental Science Symposium, UTHSCSA, April 2011

Past/Present Clients
Invited Seminars:
Robichaud TK, Fields GB. “Synthesis and Analysis of MTI-MMP Triple Helical Peptide Inhibitors” Pathology Research Conference, University of Texas Health Science Center San Antonio Pathology Department (June 18th, 2010)
Robichaud TK & Hill, B “How To Give A Great Scientific Talk” Invited Lecture, Pathobiology of Occlusive Vascular Disease Seminars, UTHSCSA (Nov 11th 2010), Cardiology Seminar Series, Texas Research Park (Feb 21st, 2011)
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Exosite Interactions Determine Matrix Metalloproteinase Specificities” Gordon-Keenan Research Seminar “Everything You Wanted to Know About Matrix Metalloproteinases But Were Afraid to Ask” Bristol, RI (Aug 6th, 2011)

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