Re: Equation for a printable titration curve

On Sat, 7 Jun 2008 08:21:17 -0700 (PDT), Mensanator
<mensanator@xxxxxxx> wrote:

On Jun 7, 5:43?am, Quentin Grady <quen...@xxxxxxxxxxxxxxx> wrote:
On Sat, 7 Jun 2008 00:18:29 -0700 (PDT), Mensanator





<mensana...@xxxxxxx> wrote:
On Jun 6, 11:29?pm, Quentin Grady <quen...@xxxxxxxxxxxxxxx> wrote:
G'day G'day Folks,

? ?I've been called upon to coach some tertiary technician students
doing inorganic chemistry. ?When tutoring electrical theory I became
familiar with Graphmatica for drawing graphs representing things like
three phase, harmonics etc. ?That was straight forward enough since
the equations were relatively simple and easy to adjust by trial and
error. ?

The curves that are produced when one titrates a weak acid with an
alkali look similar to a sigmoid curve though not so symmetrical. ?

Does anyone have a simple equation for generating curves that look
like titration curves? ?

Something like this?

<http://members.aol.com/mensanator/titration/Book2.htm>

That is fabulous. ?Thank you. ?

A couple of questions. ? ?

Did you use Graphmatica, Excel ?or another draw package to convert the
table into a graph?

Excel. I needed something quick and dirty to see
if I could reproduce something with a similar
shape. I don't know that other program but I
figured you could easily convert it once you
have the equations. Which looked like two
different forms of exponential decay, doesn't it?

True. Is that what you used to generate the table on the left?

Unfortuneately, I draw a blank on how to write
a single equation to get the shape right.

Not surprising. That may be making things unnecessarily hard for
ourselves attempting to that. I came to the conclusion last night
that I needed to tackle the graph in two parts and had a go with
Graphmatica. When I plotted the curve it gave some options for
smoothing the curve eg logistic, exponential, power law, polynomial.
None of them worked satisfactorily, which was a big surprise to me.
I could understand why this would happen with double bend. It would
"average" through both curves. Dividing it into two graphs I was sure
would get past that problem. It didn't. I'm puzzled.

You said it didn't need to be exact, just similar.

Absolutely. It a teaching tool I'm after not scientific rigor.


But hey, you could always get that book the
web site is floggin'.

Oh, which website?

I'm assuming if I used the table of putting the last Y values first
I'd get the graph where the pH (vertical value) sweeps up rather than
down in the middle. ?

If you just place them first, it will still sweep
down. You would have to reverse them in addition.

Its the graph later on in the article for
titrating a weak acid with an alkali that I'm looking for first of
all. ?

Didn't realize that. I just looked at the first one.






They don't have to be accurate, just good enough to be able to teach
the common method used to estimate the pKa of a weak acid by titration
with an alkali.

For those who would like to help being familiar with Graphmatica but
not with chemistry; I'd like to produce curves similar but not
identical to those found in the article located with the following
URL.

http://www.chemguide.co.uk/physical/acidbaseeqia/phcurves.html

Thank you and best wishes, ?
--
Quentin Grady ? ? ? ^ ?^ ?/
New Zealand, ? ? ? >#,#< [
? ? ? ? ? ? ? ? ? ? / \ /\ ? ?
"... and the blind dog was leading."

I love all the camouflage you've added for my blind dog; not that she
would have seen it.

If you're refering to those silly question marks,
that's Google, not me.

Whoops. Thought you were being very clever.
"Spot the blind dog" type joke.

Waste of time trying to hide from a blind dog.
Same as trying to win a staring contest with them.

I had a dog who went blind and inspired us all by dealing with it
magnificently. ?Life wasn't like it is in the brochures but she didn't
read brochures anyway so she insisted on leading the way on walks.

I would imagine a dog's sense of smell is as good as
your sense of sight, so no big surprise there.

Absolutely. Apparently all dogs are but a few neurons away from being
blind. Unlike cats they don't hunt by sight preferring trailing by
sent.

Best wishes,
--
Quentin Grady ^ ^ /
New Zealand, >#,#< [
/ \ /\
"... and the blind dog was leading."

http://homepages.paradise.net.nz/quentin
.

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