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buffer preparation

buffer preparation - Chemistry Forum

buffer preparation - Chemistry Forum. Discuss chemical reactions, chemistry.


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  #1  
Old 02-20-2004, 01:31 PM
Lloyd Parker
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Default buffer preparation



In article <[Only registered users see links. ]> ,
[Only registered users see links. ] (Biochemist) wrote:
You can. For example, you can prepare a pH 4.74 acetate buffer by mixing,
say, 0.5 mol of HOAc and 0.5 mol of NaOAc. Or you could start with say, 1.0
mol of HOAc and add 0.5 mol of NaOH, thereby converting 0.5 mol of the HOAc
to NaOAc.

This is why you go through a buffer region when titrating a weak acid with a
strong base (or vice-versa).
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  #2  
Old 02-20-2004, 04:43 PM
Biochemist
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Default buffer preparation

I was taught to prepare carbonate, phosphate, etc. buffers by
calculation that uses a conjugate acid/base pair. For example: to
prepare a 0.1M phosphate buffer at a given pH, I use predetermined
amounts of monosodium phosphate and disodium phosphate. Someone asked
me why I couldnt make the exact same 0.1M phosphate buffer by using
only one reagent (ie. only monophosphate form) and titrate with
HCl/NaOH to the same pH. He said he makes his Tris buffers this way. I
admit I had no good answer, so I am curious if anyone here knows if it
makes a difference.
Thanks
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  #3  
Old 02-20-2004, 06:29 PM
GeneralChemTutor
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Default re:buffer preparation

I suppose it could work if one added large amounts of the buffer
initially than added the HCl and NaOH. Relatively wasteful though.


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  #4  
Old 02-21-2004, 05:46 AM
raconte
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Default buffer preparation

[Only registered users see links. ] (Biochemist) wrote in message news:<bd2258a5.0402200843.6542770@posting.google.c om>...
I'd heard biologists say that they perfer to use two components to
make their buffers because they're worried about the effect of adding
another counterion.

Example, you prepare a 0.1 M potassium phosphate buffer using the acid
and base salts using Henderson-Hasselbach.-assuming you don't want
other thermodynamic corrections - if you do, try this:
[Only registered users see links. ]

Someone else prepares a 0.1 M buffer from the acid potassium salt that
has been titrated up with sodium hydroxide. Same pH, same phosphate
molarity, but the mix of sodium and potassium ions could affect a
living system differently.

Now try this: Someone else does the same, but overshoots with the
hydroxide and has to go back with ... oh, what acid is around
here...dang out of phosphoric acid...oh well, a few drops of conc.
sulfuric acid is ok...it will be the right molarity at the end anyway
....

In the end, all you want is a consistant preparation method to avoid
surprises. Innovate as little as possible.
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  #5  
Old 02-22-2004, 10:42 PM
Bruce Sinclair
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Default buffer preparation

In article <[Only registered users see links. ] >, [Only registered users see links. ] (raconte) wrote:
(snip)

VERY good advice here. Once you have a method that works, don't change
it Luckily, you've writen down exactly what you have done so others
can do it too

Bruce

-----------------------------------------------------------------------
It was so much easier to blame it on Them. It was bleakly depressing to
think that They were Us. If it was Them, then nothing was anyones fault.
If it was Us, what did that make Me ? After all, Im one of Us. I must be.
Ive certainly never thought of myself as one of Them. No-one ever thinks
of themselves as one of Them. Were always one of Us. Its Them that do
the bad things. <=> Terry Pratchett. Jingo.
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