Bill, You still lose a point for missing the fourth pKa in ammonium citrate, the ammonium ion.
Kind regards, Pete -----Original Message----- From: CCP4 bulletin board on behalf of William G. Scott Sent: Sat 8/9/2008 12:09 PM To: [email protected] Subject: Re: [ccp4bb] Ammonium citrate tribasic buffer Well, as long as I was right. That is the important thing. ;) William G. Scott Contact info: http://chemistry.ucsc.edu/~wgscott/ On Aug 9, 2008, at 11:11 AM, Ian Tickle wrote: > > I think the problem is that Britannica, or even Wikipedia, is and > has never been the final arbiter of truth, I would put my faith in a > specialist publication such as: > > http://books.google.co.uk/books?id=bwbCVCFPNI4C&pg=PA175&lpg=PA175&dq=%22karl+hasselbalch%22&source=web&ots=yHzTUiNE1g&sig=7JmNU-OfHIkmXxR5ivGTrpS7_Us&hl=en&sa=X&oi=book_result&resnum=5&ct=result > > -- Ian > >> -----Original Message----- >> From: [EMAIL PROTECTED] >> [mailto:[EMAIL PROTECTED] On Behalf Of William Scott >> Sent: 07 August 2008 23:27 >> To: Juergen Bosch >> Cc: [email protected] >> Subject: Re: [ccp4bb] Ammonium citrate tribasic buffer >> >> Wikipedia claims Hasselbach is a misspelling: >> >> http://en.wikipedia.org/wiki/Henderson-Hasselbalch_equation >> >> Since Wikipedia has now replaced the social consensus as the final >> arbiter of truth ... >> >> >> On Aug 7, 2008, at 3:22 PM, Juergen Bosch wrote: >> >>> Just on a side note, can someone clarify why Hasselbach is not >>> Hasselbalch or vice versa ? Or is that the same guy just somewhere >>> sometime misspelled and for ever in the records ? >>> >>> See here: >>> >> http://www.britannica.com/EBchecked/topic/261188/Henderson-Has > selbach-equation >>> >>> Jürgen >>> >>> >>> On 7 Aug 2008, at 15:12, [EMAIL PROTECTED] wrote: >>> >>>> Good points! >>>> >>>> Not only citrate is inappropriate for buffers in the pH 6.5-7.5 >>>> range, >>>> but also (as pointed out by your colleagues at UCSC, but >> probabbly >>>> elsewhere, >>>> polyprotic acids are hard to handle, as their pKa change in a >>>> significant >>>> fashion depending on their concentration. >>>> >>>> In this case, the Henderson-Hasselbalch equation must be >> written in >>>> terms >>>> of activities rather than concentrations, otherwise it is totally >>>> useless. >>>> >>>> Nadir Mrabet >>>> >>>> >>>> >>>> Selon "William G. Scott" <[EMAIL PROTECTED]>: >>>> >>>>> There are 3 pKa's for citric acid: >>>>> >>>>> 3.15, 4.77, and 5.19 >>>>> >>>>> so it is going to be a lousy buffer at pH 6.7 to 7.25. >> Also, you >>>>> need >>>>> to know what concentration your buffer is, and whether that >>>>> concentration is with respect to the citrate ion or what. It >>>>> won't be >>>>> tribasic with respect to ammonium ion near neutral pH. >>>>> >>>>> So if for example you need 1M of this buffer, the simplest thing >>>>> to do >>>>> is make up a 1M stock solution of tribasic ammonium >> citrate and a 1M >>>>> stock solution of of citric acid and then mix the two >> together. You >>>>> can calculate the ratio using the Henderson-Hasselbalch >> equation or >>>>> just titrate one into the other while stirring in the >> presence of >>>>> a pH >>>>> electrode. >>>>> >>>>> (You'll have to use the pH electrode approach if you took >>>>> introductory >>>>> chemistry from anyone other than me at UCSC since my colleagues >>>>> think >>>>> that polyprotic acids are too stressful for our undergrads.) >>>>> >>>>> >>>>> William G. Scott >>>>> >>>>> Contact info: >>>>> http://chemistry.ucsc.edu/~wgscott/ >>>>> >>>>> >>>>> On Aug 7, 2008, at 12:42 PM, E rajakumar wrote: >>>>> >>>>>> Dear All >>>>>> Sorry for non crystallographic query. >>>>>> Can any body mail me how to prepare Ammonium citrate >>>>>> tribasic (citric acid triammonium salt) buffer pH 6.7 >>>>>> to 7.25 and also what is the pKa value. >>>>>> Thanking you in advance >>>>>> Rajakumara >>>>>> >>>>>> >>>>>> >>>>>> E. Rajakumara >>>>>> Postdoctoral Fellow >>>>>> Strcutural Biology Program >>>>>> Memorial Sloan-Kettering Cancer Center >>>>>> New York-10021 >>>>>> NY >>>>>> 001 212 639 7986 (Lab) >>>>>> 001 917 674 6266 (Mobile) >>>>>> >>>>>> >>>>>> >>>>>> Get your new Email address! >>>>>> Grab the Email name you've always wanted before >> someone else >>>>>> does! >>>>>> http://mail.promotions.yahoo.com/newdomains/aa/ >>>>> >>>> >>>> >>>> Pr. Nadir T. 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