[CHM 112] Chapter 17 powerpoint

[Andrew J. Pounds]

In slide 8 we did not have any conjugate base in the system at the
beginning of the system.  This is an unbuffered system.  I was
demonstrating hoe the pH would drop quickly in this case if we added a
small amount of acid.  We just dumped hydronium ions into an unbuffered
system so they had to be represented in the initial condtions of the
reaction.

Understand this -- when you add strong base strong acid to a buffer
system the system is going to react almost instantaneosly to that
"stress" (that is why we do the calculations for the new initial
conditions first) and then the system will respond to these new
conditions to attain equilibrium.

In slide 12 we are working with a buffer.  There is weak acid present
and the conjugate base of the weak acid.   When we ADD a strong acid it
will go into the system as hydronium ions (on the right) and the system
will respond by making more weak acid (by consuming the conjugate base
of the waak acid).  That is why in that case we subtracted from the
conjugate base and added to the weak acid.

On slide 35 the $x$ value is the amount of conjugate base added to the
system in liters.  0.0624 liters is 62.4 ml.

$1.66 = \frac{(.50)(.0624)}{(.50)(.100-0.0624)} =\frac{0.0312}{0.0188}=
1.66$

On 04/19/2018 03:41 PM, wrote:
>
> Hello Dr. Pounds I have some questions about the information on our
> powerpoint for chapter 17. On slide 12 of the powerpoint, the strong
> acid HCl is added to a buffer solution. In order for us to calculate
> the new initial concentration, we subtracted the number of moles of
> H^+ by the initial concentrations in the solution before dividing by
> the total volume. My question is why do we do it that way on slide 12
> but on slide 8 we do it another way? When .50M of HCl is added to the
> solution in slide 8 we just put the added acid in under H30^+ in the
> ICE table. 
>
>
> My next question is on slide 35 how did you find the buffer mix in ml?
> when I plug in the values of x into the equation of each concentration
> I don't get the same answers you got. 
>
>

-- 
Andrew J. Pounds, Ph.D.  (pounds_aj at mercer.edu)
Professor of Chemistry and Computer Science
Mercer University,  Macon, GA 31207   (478) 301-5627
http://faculty.mercer.edu/pounds_aj

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://theochem.mercer.edu/pipermail/chm112/attachments/20180419/2220dd32/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: mhfcjcoknbbofjmn.png
Type: image/png
Size: 605 bytes
Desc: not available
URL: <http://theochem.mercer.edu/pipermail/chm112/attachments/20180419/2220dd32/attachment.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: kbbmjmjpdghnofgm.png
Type: image/png
Size: 1747 bytes
Desc: not available
URL: <http://theochem.mercer.edu/pipermail/chm112/attachments/20180419/2220dd32/attachment-0001.png>