Science Forums Biology Forum Molecular Biology Forum Physics Chemistry Forum Strange buffer properties

 Chemistry Forum Chemistry Forum. Discuss chemical reactions, chemistry.

# Strange buffer properties

## Strange buffer properties - Chemistry Forum

### Strange buffer properties - Chemistry Forum. Discuss chemical reactions, chemistry.

#1
02-08-2004, 01:17 PM
 Oscar Lanzi III Guest Posts: n/a
Strange buffer properties

You have to consider the overall ionization scheme. You have two
sources of protons going on here, the water and the acetic acid.

Say you have one mole of CH3COONa and 1 mole of CH3COOH mixed in with
100 liters of water. Then you have in solution the following species:

a moles per liter of CH3COOH
b moles per liter of CH3COO(-)
c moles per liter of H(+)
d moles per liter of OH(-)
e moles per liter of Na(+)

The Na(+) from the sodium acetate does not react with anything, so e =
0.01. That leaves four unknowns governed by the following equations:

a + b = 0.02 to balance the acetate ions
c + 0.01 = b + d to balance charges
b*c = K_a*a from acetic acid dissociation
c*d = K_w from water dissociation

I won't go through the mathematical detailsof the solution to this
nonlinear system, but what happens is that because K_w is so small, c
and d are both much smaller than 0.01 and then you can assume that the
second equation is reducible to b = 0.01. Then a = 0.01 and the third
equation leads to the "standard" buffer pH.

But now suppose that instead of 100 liters of water there are 10^6 or
10^9 liters. Then 0.01 is correspondingly replaced by 10^(-6) or
10^(-9) above, and these become small enough so that c and d are no
longer negligible in the second equation even with their product K_w as
small as 10^(-14). In other words, dissociation of the water is
becoming important, competing with dissociation of the acetic acid for
generation of the protons. That's when the standard buffering
approximation breaks down and the pH begins to reflect that of pure
water.

Real lakes have other buffers acting from their impurities (natural and
pollution). But that is another story.

--OL

 Tags buffer , properties , strange

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home General Science Forums     Biology Forum     New Member Introductions Forum     Chemistry Forum         Organic Chemistry Forum     Physics Forum     General Science Questions and Layperson Board         Science and Religion Forum         Zoology Forum     Environmental Sciences and Issues General Forum     Chit Chat         Science and Lab Jokes     Article Discussion     Molecular Biology News and Announcements         Conferences , Symposiums and Meetings         Molecular Station Suggestion Forum         Instructions for Posting, Help, and Frequently Asked Questions     Science News and Views         Molecular Biology Lectures and Videos     Science Careers         Post-doctoral         Medical School         Ph.D Doctor of Philosophy         Science Jobs Forum Molecular Research Topics Forum     PCR - Polymerase Chain Reaction Forum         Real-Time PCR and Quantitative PCR Forum     Bioinformatics         BioStatistics Forum     Molecular Biology Techniques         Molecular Cloning Forum         Electrophoretic Mobility Shift Assay Forum         Agarose Gel Electrophoresis Forum         BioPhysics Forum         Gene Therapy     Cell Biology and Cell Culture         Apoptosis, Autophagy, and Necrosis Forum         Flow Cytometry Forum         Transfection Forum         Confocal - Microscopy Imaging Techniques         Immunology and Host-Pathogen Interactions         Signalling Biology         Stem Cell Forum     Basic Lab Protocols and Techniques         SDS-PAGE Gel Electrophoresis Forum     DNA Techniques         DNA Extraction Forum         cDNA Forum     Epigenetics Forum: DNA Methylation, Histone and Chromatin Study         ChIP Chromatin Immunoprecipitation Forum     Protein Science         Antibody Forum             Immunoprecipitation Forum         Western Blot Forum         Protein Crystallography Forum         Recombinant Protein Forum         ELISA Assay Forum         Protein Forum     Proteomics Forum         Peptide Forum         Mass Spectrometry Forum         2-D Gel Electrophoresis Forum     Omics and Genomics Forum         Microarrays Forum         Genomics Forum     RNA Techniques Forum         RNAi and SiRNA Forum     Histology Forum         Immunohistochemistry Forum         Immunocytochemistry Forum         Electron Microscopy Forum         Immunofluorescence Forum     Protocols and Methods Forum     Molecular Biology Articles and Protocols     Animal and Molecular Model Systems         Drosophila Forum         Yeast Forum         Zebrafish Forum         Botany Forum         C Elegans Forum         Arabidopsis and Plant Biology         Microbiology Forum         Knockout Mouse Forum     Chromatography Forum Products and Vendor Discussion     Molecular Biology Products and Vendors         Bad Product/Service? Post Here         Lab Equipment Discussion and Reviews Regional Molecular Biology Discussion     Forum Chemie     Forum Biologie     Forum Biologia     Forum Chimica     Forum Physik     Forum De Chimie     Forum De Physique     Forum Chemia     中国人分子的生物学论坛 Chinese     Greek Molecular Biology Forums     分子生物学のフォーラム Japanese     ميدان فارسى. Persian Molecular Biology     [أربيك] علم ساحة- Arabic     Forum de Biologie Moleculaire     Forum Biologia Molecolare     Forum die Molekularbiologie     Foro Biologia Molecular

 Similar Threads Thread Thread Starter Forum Replies Last Post Cellbiogal Antibody Forum 2 01-08-2009 09:52 PM William Penrose Chemistry Forum 0 02-05-2004 02:20 PM friendŽ Chemistry Forum 0 02-04-2004 05:53 AM Barry Chemistry Forum 0 02-03-2004 09:57 PM Louis Hom Chemistry Forum 0 02-03-2004 05:48 PM

All times are GMT. The time now is 03:34 AM.

 Contact Us - Molecular Biology - Archive - Privacy Statement - Top