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Chemistry (including Biochemistry)/Help with Hydronium and Hydroxide Ions


QUESTION: Hi I'm a AP Chemistry student and I just don't understand this concept. I think its suppose to be an easy concept but I just don't understand it.

For example

HNO2 + H20 ----> H30+ NO2-

I don't understand how the hydronium ions form. How do I figure out if a OH- or H30+ will form from the reactant side.

ANSWER: Hi Pratik!

Khan Academy is an excellent chemical education resource. I rave about them all the time. I recommend you take a look here at 'introduction to acids and bases' as well as 'conjugate acids and bases'.

The other hint here is this. When you look at a chemical reaction like this, realize that it's going to be ions rearranging in water. H2O can act as itself OR form H and OH-. HNO2 can form NO2- and H+.

NO2- is a weak base and H+ is a strong acid. After neutralizing any OH-s that are naturally around in the water system, the only place for a 'lonely' H+ to go ... is to stick onto an H2O-acting-like-a-base like a third wheel.

This reaction is a little confusing, but it makes 'sense' if you consider that H+ is a much stronger acid than H2O, so H2O in this case acts as a base.

Does that make sense?

---------- FOLLOW-UP ----------

QUESTION: Okay I think I do but let me just ask if this is a logical way to look at it.

HNO2 has one less H than H20 so it will become H30+

RNH3 + H2O will form an OH- Ion because RNH2 has one more H than H20.

So basically if I look at the reactant, and compare how many H+ ions it has compared to water, can i just assume what will form?

I'm only going to be working with one reactant that will have water added to it.

So if main reactant has more H+ than H20 that would form an OH-
If main reactant has less H+ ion than H20 that would form H30

Am I allowed to look at it that way?

Sadly, while that might work in some cases, it's not true in ALL cases. So not really, no.

Water (H2O) is a special case: just as it is, without splitting, it may be considered both an acid or a base.

Any time you move H+'s around AT ALL you have an acid base reaction. In acid base reactions you have an acid reactant and a base reactant on the reactant side, and an acid product and a base product on the product side. These can be matched up.

Your thinking ideally would go:

HNO2 + H20 ----> H30+ + NO2-
Acid  +  Base ----> Acid + Base

Which one is the acid? The one with a donateable H+.

When an acid and base react, they form what is known as the acid base conjugates. (Why I linked you that Khan video.) An acid reactant such as HNO2 has a conjugate base of NO2-. The water here goes from H2O to H3O+. Since H3O+ is positively charged and can donate a H+, it is the conjugate acid, and H2O is the base.

This is true for all cases.

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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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