Hi Pete:
The pKa (NH4OH) is about 9, so it shouldn't be relevant to the buffer
calculation. The ammonia gas equilibrium would be a reason not to use
this as a buffer, however.
Bill
William G. Scott
Contact info:
http://chemistry.ucsc.edu/~wgscott/
On Aug 9, 2008, at 2:54 PM, Dunten, Pete W. wrote:
> 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: [log in to unmask]
> 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: [log in to unmask]
>>> [mailto:[log in to unmask]] On Behalf Of William Scott
>>> Sent: 07 August 2008 23:27
>>> To: Juergen Bosch
>>> Cc: [log in to unmask]
>>> 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, [log in to unmask] 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" <[log in to unmask]>:
>>>>>
>>>>>> 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. Mrabet
>>>>> Cellular & Molecular Biochemistry
>>>>> INSERM U-724
>>>>> UHP - Nancy 1, School of Medicine
>>>>> 54505 Vandoeuvre-les-Nancy Cedex
>>>>> France
>>>>> Tel : +33 (0)3.83.68.32.73
>>>>> Fax : +33 (0)3.83.68.32.79
>>>>> E-mail : [log in to unmask]
>>>>
>>>> -
>>>> Jürgen Bosch
>>>> University of Washington
>>>> Dept. of Biochemistry, K-426
>>>> 1705 NE Pacific Street
>>>> Seattle, WA 98195
>>>> Box 357742
>>>> Phone: +1-206-616-4510
>>>> FAX: +1-206-685-7002
>>>> Web: http://faculty.washington.edu/jbosch
>>>
>>>
>>
>>
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