[Catalist] WACE: ATAR Year 12 Chemistry: Buffer Solutions

Fri May 19 20:13:36 AEST 2017

Hi all, especially Mike.

I am not that unhappy about the lack of numerical approaches in 
buffering. The type of rate calculations that I mentioned in my past 
post are way too complex for even 1st year Uni.

I would like a bit more emphasis on linking pKa and pH, particularly the 
equation pH = pKa + log [H+][A-]/HA which predicts that an equimolar 
concentration of acid/conjugate base will have a pH that is set by the 
strength of its ionisation constant. This is incredibly predictive, and 
allows you to chose an appropriate buffer system for any situation you 
need. It also explains why we tell our kids that buffers only really 
work within 1 pH unit of pKa. It is also a simple, low hanging fruit.

pKa's are not explicitly in the curriculum, (although they appear in the 
Nelson book, and are worthwhile given we have taught pH).

We always have this tussle between rigor and relevance. Now it seems 
that there is a tend to pursue rigor. Although note: by labelling any 
dingy dry dank collection of factoids rigorous, you can persuade people 
to over-pack their curricula. Many people (myself includes) feel that 
the SHE aspects of our current courses have not been well done, and have 
led to little improvement in student understanding at WACE level. The 
danger with this is that calling for that kind of SHE reform may lead to 
incredibly turgid, "math monkey" - favouring curricular that divert 
students with the potential to be quite creative, innovative and 
successful chemists from the course. I have seen more than on struggling 
student, sitting in the high 60s, blossom into gifted chemists at 
university. I also know a number of straight A chemistry students who 
know next to nothing about chemistry, 5 years plus out from the last 
exam.  The important thing is to ensure that faux "rigor" dousn't choke 
our courses. Also to make sure that we don't get "committee rigor", 
where everybody's pet area gets incorporated and the whole thing becomes 
unteachable, and joyless to learn.

My personal preference would be to teach in depth some chemistry that 
can be a template for future efforts. Such would include a really good 
separation (getting an antibiotic out of a broth, or perhaps citric acid 
from culture on cornsteep licquor), a good organic synthesis (preferably 
4 or 5 steps, plus work up), managing and remediating an algal bloom, 
gold separation, wine chemistry, etc. It isn't SHE, but it is where I 
would have liked to see it go. But focus on the processes, then bring in 
societal stuff and people, as a sideline. If you want to see how this is 
done well, albeit at a simpler level, check out the RSC's Chemistry In 
Its Element series.

As to the textbooks: If it ain't in the curriculum, a textbook includes 
it at its great peril. I think the lamentable state of textbooks relates 
more to the curriculum design process. Look at the curriculum guidelines 
- they are vague crap statements, designed to comply with an 
ideological/theoretical model that is unviable in a production 
environment such as a school. You can't jump onto the textbook writers 
because, they like us, are just trying to read the tea leaves. 
Nevertheless, I know the sense of anger at using a poorly written and 
factually incorrect textbook. There just isn't the advance notice of new 
content, and there isn't the proper multi-level review of textbook, 
teacher materials and sample texts. Worse, there isn't time for those 
skilled in schools to deploy their talents to fix it - when was the last 
working year you had when you averaged under 45h a week? 1988 wasn't it?

Have a nice weekend! I am going frog watching!

Cheers,
Leon

On 19/05/2017 4:12 PM, Michael McGarry wrote:
>
> Greetings Science Colleagues,
>
> “Buffer solutions are conjugate in nature and resist changes in pH 
> when small amounts of strong acid or base are added to the solution; 
> buffering capacity can be explained*qualitatively*; Le Châtelier’s 
> Principle can be applied to predict how buffers respond to the 
> addition of hydrogen ions and hydroxide ions.” [Page 12]
>
> Reference: SCSA WACE ATAR URL: 
> http://wace1516.scsa.wa.edu.au/__data/assets/pdf_file/0012/10605/Chemistry-Y12-Syllabus-AC-ATAR-GD.pdf
>
> A recent post to STAWA’s CATALIST e-forum motivated me to ask these 
> two Questions.
>
> Question 1: Would a significant proportion of Australian Year 12 
> secondary chemistry students have the mathematical skills to be able 
> to satisfactory explain *quantitatively* buffering capacity?
>
> Question 2: Do the commercially available Year 12 Chemistry textbooks 
> written for the SCSA WACE ATAR Year 12 Chemistry syllabus include a 
> text section that explains *quantitatively* buffering capacity?
>
> *Useful URL’s on Buffer Solutions*
>
> URL 1: http://www.mhhe.com/physsci/chemistry/chang7/ssg/chap16_2sg.html
>
> URL 2: 
> https://www.chem.purdue.edu/gchelp/howtosolveit/Equilibrium/Buffers.htm
>
> URL 3: http://scifun.chem.wisc.edu/CHEMWEEK/BioBuff/BioBuffers.html
>
> URL 4: https://www.rose-hulman.edu/~brandt/Chem330/pH_and_Buffers.pdf 
> <https://www.rose-hulman.edu/%7Ebrandt/Chem330/pH_and_Buffers.pdf>
>
> URL 5: 
> http://virtuallaboratory.colorado.edu/CLUE-Chemistry/chapters/chapter9txt-2.html
>
> URL 6: 
> https://www.chem.purdue.edu/courses/chm333/Spring%202013/Lectures/Spring%202013%20Lecture%205.pdf
>
> URL 7: 
> http://www.ulm.edu/chemistry/courses/manuals/chem1010/experiment_09.pdf
>
> URL 8: 
> https://www.une.edu.au/__data/assets/pdf_file/0003/121728/chemistry-teacher-notes-answers.pdf
>
> Best Wishes,
>
> Michael John McGarry
>
>
>
> _______________________________________________
> Catalist mailing list
> Catalist at lists.stawa.net
> http://lists.stawa.net/mailman/listinfo/catalist_lists.stawa.net

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.stawa.net/pipermail/catalist_lists.stawa.net/attachments/20170519/c78640bc/attachment.html>