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Guest
Posted: Tue May 09, 2006 12:49 pm
 
What is a buffer capacity? And how to calculate it? Buffer is 0.1M
pH=5.0 acetic.
 
Jimchip
Posted: Tue May 09, 2006 6:35 pm
 
On 2006-05-09, smunny@spet.info.pl <smunny@spet.info.pl> wrote:
[quote:e11bebfaf3]What is a buffer capacity? And how to calculate it? Buffer is 0.1M
pH=5.0 acetic.
[/quote:e11bebfaf3]
I'll ask a question:
How much of a strong acid like HCl(aq) will it take to (pretty much)
protonate the acetate ions in solution such that any further addition of HCl
will result in a rapid (/ml) lowering of the pH ?

--
Answers in 5 seconds, please, but don't watch the clock Smile
 
Bob
Posted: Tue May 09, 2006 9:15 pm
 
On 9 May 2006 11:49:39 -0700, smunny@spet.info.pl wrote:

[quote:b2de223233]What is a buffer capacity? And how to calculate it? Buffer is 0.1M
pH=5.0 acetic.
[/quote:b2de223233]
Interesting that you ask. Another thread on this topic recently (may
have been in another chem forum), and the conclusion was that there is
no generally accepted quantitative definition of buffer capacity. (I
assume you understand the general idea of what the buffer does.)

So if someone asked you this, the first step is to find out how they
define buffer capacity.

bob
 
Borek
Posted: Wed May 10, 2006 2:40 am
 
On Wed, 10 May 2006 05:15:24 +0200, Bob <bbx107.XYZ@excite.XYZ.com> wrote:

[quote:2f11e37e18]What is a buffer capacity? And how to calculate it? Buffer is 0.1M
pH=5.0 acetic.

Interesting that you ask. Another thread on this topic recently (may
have been in another chem forum), and the conclusion was that there is
no generally accepted quantitative definition of buffer capacity.

So if someone asked you this, the first step is to find out how they
define buffer capacity.
[/quote:2f11e37e18]
http://www.chembuddy.com/?left=pH-calculation&right=pH-buffer-capacity

But as you have stated - there are numerous ways to define buffer
capacity, so without knowing which definition should be used it is hard to
help.

Best,
Borek
--
http://www.chembuddy.com
http://www.ph-meter.info/pH-Nernst-equation
http://www.terapia-kregoslupa.waw.pl
 
Unknown
Posted: Wed May 10, 2006 6:06 am
 
On Wed, 10 May 2006 00:35:55 -0000, Jimchip
<jimchip@ifthisisavalidhostname.com.invalid> wrote:

[quote:a2f50a6f57],;On 2006-05-09, smunny@spet.info.pl <smunny@spet.info.pl> wrote:
,;> What is a buffer capacity? And how to calculate it? Buffer is 0.1M
,;> pH=5.0 acetic.
,;
,;I'll ask a question:
,;How much of a strong acid like HCl(aq) will it take to (pretty much)
,;protonate the acetate ions in solution such that any further addition of HCl
,;will result in a rapid (/ml) lowering of the pH ?
[/quote:a2f50a6f57]
Well all you need to do is plot the titration curve and then apply
your definition of "rapid".
 
mail.uni-wuppertal.de
Posted: Wed May 10, 2006 8:04 am
 
"Borek" <m.borkowski@delete.chembuddy.these.com.parts> schrieb im
Newsbeitrag news:op.s9budzs826l578@borek...
[quote:a38ccd7cd0]On Wed, 10 May 2006 05:15:24 +0200, Bob <bbx107.XYZ@excite.XYZ.com> wrote:

What is a buffer capacity? And how to calculate it? Buffer is 0.1M
pH=5.0 acetic.

Interesting that you ask. Another thread on this topic recently (may
have been in another chem forum), and the conclusion was that there is
no generally accepted quantitative definition of buffer capacity.

So if someone asked you this, the first step is to find out how they
define buffer capacity.

http://www.chembuddy.com/?left=pH-calculation&right=pH-buffer-capacity

But as you have stated - there are numerous ways to define buffer
capacity, so without knowing which definition should be used it is hard to
help.

Best,
Borek
--
http://www.chembuddy.com
http://www.ph-meter.info/pH-Nernst-equation
http://www.terapia-kregoslupa.waw.pl
[/quote:a38ccd7cd0]
Borek,

I looked at your site and especially like the way you emphasize the
different ideas about what buffer capacity is. I disagree strongly, though,
that it is counterintuitive to have differing buffer capacities for addition
of acid and base. Nothing could be more obvious. To those who have already
spent some time thinking about it, of course.

I don't understand what use there is in reckoning buffer capacity from the
derivative (your equation 19.1). After all, the reason I want to know the
capacity is so that I will know how much acid or base can be added or can
arise through reaction without moving the pH more than a specified distance
from the preferred value.

In exercise classes and on exams I never ask students to reckon buffer
capacity as such. I always ask whether the solution is sufficiently buffered
to avoid a pH change of more than a certain number of units when a specified
amount of acid or base is added.

I find it is easy and clear to the students to solve such examples with the
log term of the Henderson-Hasselbalch equation. You start with the original
concentrations of the acid and base forms and calculate the new log term
after one concentration increases and the other decreases by the added
amount of acid or base.

All these methods and calculations are in truth only relevant for
activities, and these are particularly hard to account for when the pH of a
buffer is changing and with it the ionic strength. In practice, I do what
most textbooks do: I remind the students of the importance of activity for
the calculations, but say we can't spend the necessary time without
neglecting many other important topics of the course.

The buffer capacity based on a pH change of one unit (the derivative
calculation) is only valid for tiny additions of acid or base. Extending
this to what actually happens when larger amounts are added can lead to
hilarious results.

A glance at the buffer region on the titration curve for a weak acid gives
an idea of how great a change is involved when the pH changes by a whole
unit: it shoves the system out of the range where the Henderson-Hasselbalch
equation is valid. For biological systems or for kinetics experiments, a pH
change of a whole unit would be overwhelming.
 
Jimchip
Posted: Wed May 10, 2006 8:45 am
 
On 2006-05-10, Unknown <dwilkins@unitelc.com> wrote:
[quote:551b414c3c]On Wed, 10 May 2006 00:35:55 -0000, Jimchip
jimchip@ifthisisavalidhostname.com.invalid> wrote:

,;On 2006-05-09, smunny@spet.info.pl <smunny@spet.info.pl> wrote:
,;> What is a buffer capacity? And how to calculate it? Buffer is 0.1M
,;> pH=5.0 acetic.
,;
,;I'll ask a question:
,;How much of a strong acid like HCl(aq) will it take to (pretty much)
,;protonate the acetate ions in solution such that any further addition of HCl
,;will result in a rapid (/ml) lowering of the pH ?

Well all you need to do is plot the titration curve and then apply
your definition of "rapid".
[/quote:551b414c3c]
Not moi :)

--
Sometimes a question does help with an answer.
 
Borek
Posted: Wed May 10, 2006 9:21 am
 
On Wed, 10 May 2006 16:04:13 +0200, mail.uni-wuppertal.de
<turner@uni-wuppertal.de> wrote:

[quote:a5059ff7e7]http://www.chembuddy.com/?left=pH-calculation&right=pH-buffer-capacity

I looked at your site and especially like the way you emphasize the
different ideas about what buffer capacity is. I disagree strongly,
though,
that it is counterintuitive to have differing buffer capacities for
addition
of acid and base. Nothing could be more obvious. To those who have
already spent some time thinking about it, of course.
[/quote:a5059ff7e7]
All depends on intuition. For me there is ONE buffer capacity, not TWO. If
there is one buffer capacity it should be the same regardless of what I
add to the buffer, especially as regardless of what I add the same
property - pH - changes. If the buffer capacity is different depending on
whether you add base or acid you have in fact TWO buffer capacities and
you should state which one you use every time you use it.

[quote:a5059ff7e7]I don't understand what use there is in reckoning buffer capacity from
the
derivative (your equation 19.1). After all, the reason I want to know the
capacity is so that I will know how much acid or base can be added or can
arise through reaction without moving the pH more than a specified
distance from the preferred value.
[/quote:a5059ff7e7]
"Specified distance" is hardly precise. Is it 0.2 pH unit, or 0.01 pH
unit? Depending on the application and its requirements you have two
different definitions and you have to specify each time which definition
you use. But someone may need "specified distance" of 0.1 unit, and lo -
there is third definition and you can't agree on what the buffer capacity
is.

That's why I like approach described on my page - and that's why the
differential definition is IMHO (and probably in prof. Hulanicki opinion
Wink ) better. It is unambiguous.

[quote:a5059ff7e7]The buffer capacity based on a pH change of one unit (the derivative
calculation) is only valid for tiny additions of acid or base. Extending
this to what actually happens when larger amounts are added can lead to
hilarious results.
[/quote:a5059ff7e7]
Derivative definition doesn't use 1 unit pH change, it uses
infinitesimally small pH change!

Best,
Borek
--
http://www.chembuddy.com
http://www.ph-meter.info/pH-Nernst-equation
http://www.terapia-kregoslupa.waw.pl
 
Guest
Posted: Wed May 10, 2006 10:15 am
 
Borek wrote:
[quote:61844ff6a1]On Wed, 10 May 2006 05:15:24 +0200, Bob <bbx107.XYZ@excite.XYZ.com> wrote:

http://www.chembuddy.com/?left=pH-calculation&right=pH-buffer-capacity
[/quote:61844ff6a1]
So if I will write 0.053 it will be OK?
 
Borek
Posted: Wed May 10, 2006 10:23 am
 
On Wed, 10 May 2006 18:15:13 +0200, <smunny@spet.info.pl> wrote:

[quote:0438d2a398]http://www.chembuddy.com/?left=pH-calculation&right=pH-buffer-capacity

So if I will write 0.053 it will be OK?
[/quote:0438d2a398]
It MAY be OK, as it is not clear what you are asked about. It may be as
well 42, which is ultimate answer to everything ;)

What was buffer capacity definition used by your lecturer?

Best,
Borek
--
http://www.chembuddy.com
http://www.ph-meter.info/pH-Nernst-equation
http://www.terapia-kregoslupa.waw.pl
 
Guest
Posted: Thu May 11, 2006 10:13 am
 
Borek wrote:
[quote:b357ec2f1f]On Wed, 10 May 2006 18:15:13 +0200, <smunny@spet.info.pl> wrote:

http://www.chembuddy.com/?left=pH-calculation&right=pH-buffer-capacity

So if I will write 0.053 it will be OK?

It MAY be OK, as it is not clear what you are asked about. It may be as
well 42, which is ultimate answer to everything ;)

What was buffer capacity definition used by your lecturer?
[/quote:b357ec2f1f]
None, she just asked the question. It is for an extra credit but I need
it badly Sad
 
Borek
Posted: Thu May 11, 2006 11:18 am
 
On Thu, 11 May 2006 18:13:35 +0200, <smunny@spet.info.pl> wrote:

[quote:aba2d2af36]http://www.chembuddy.com/?left=pH-calculation&right=pH-buffer-capacity

So if I will write 0.053 it will be OK?

It MAY be OK, as it is not clear what you are asked about. It may be as
well 42, which is ultimate answer to everything ;)

What was buffer capacity definition used by your lecturer?

None, she just asked the question. It is for an extra credit but I need
it badly Sad
[/quote:aba2d2af36]
If it is for an extra credit and it was not explained probably any answer
will do - as long as you can show source of the definition used and you
can convince her that's the correct one ;)

Best,
Borek
--
http://www.chembuddy.com
http://www.ph-meter.info/pH-Nernst-equation
http://www.terapia-kregoslupa.waw.pl
 
Jimchip
Posted: Thu May 11, 2006 6:04 pm
 
On 2006-05-11, smunny@spet.info.pl <smunny@spet.info.pl> wrote:
[quote:792b3d7e21]
Borek wrote:
On Wed, 10 May 2006 18:15:13 +0200, <smunny@spet.info.pl> wrote:

http://www.chembuddy.com/?left=pH-calculation&right=pH-buffer-capacity

So if I will write 0.053 it will be OK?

It MAY be OK, as it is not clear what you are asked about. It may be as
well 42, which is ultimate answer to everything ;)

What was buffer capacity definition used by your lecturer?

None, she just asked the question. It is for an extra credit but I need
it badly Sad
[/quote:792b3d7e21]
Extra Credit?! Well, then... just try to come up with "Anything" reasonable,
under any definition you want. Define your terms and show you understand the
concepts...

--
I thought it was one of those "we need to know what your idiot teacher
wants" kind of question.
 
Guest
Posted: Mon May 15, 2006 6:02 am
 
Borek wrote:
[quote:005a0aba8a]On Thu, 11 May 2006 18:13:35 +0200, <smunny@spet.info.pl> wrote:

http://www.chembuddy.com/?left=pH-calculation&right=pH-buffer-capacity

So if I will write 0.053 it will be OK?

It MAY be OK, as it is not clear what you are asked about. It may be as
well 42, which is ultimate answer to everything ;)

What was buffer capacity definition used by your lecturer?

None, she just asked the question. It is for an extra credit but I need
it badly :(

If it is for an extra credit and it was not explained probably any answer
will do - as long as you can show source of the definition used and you
can convince her that's the correct one Wink
[/quote:005a0aba8a]
THANK YOU MR. BOREK I HAVE USED INFO FROM THAT PAGE AND IT WORKED
Smile))))))))))))))))))))
 
 
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