Week of 1/26

Monday: Finished with the buffer packet, specifically Henderson-Hasselbach, how to design a buffer and being very clear about what species are present in solutions. Here’s the notes. Rest of class you worked on homework.  Buffer Video link from Caroline V.

Tuesday: Today was short so we just went over titration math.  Here’s the notes.  HW: book problems from unit outline.

Wednesday: (NOTES)Today we went over titration curves  – specifically what is present at each spot on the curve. I showed how one would do this with a strong acid/strong base combo and then I had you break up into groups and draw a titration curve for weak acids and bases.  It took nearly all class for you guys to make your pictures, and in the last 10 min we compared each of them and wrote down some quick observations: titrations of weak acids will have a basic pH at the equivalence point because all of the weak acid has become its conjugate base.  All weak bases will have an acidic pH at the equivalence point because all weak bases will have become the conjugate acid.  We also noticed that the flat part in the beginning is flat because it is acting as a buffer as their is both conjugate acid and base present.  Once the buffer is “used up” / reaches the buffer capacity, the graph spikes with addition of strong titrant.

Today’s questions that you should be able to answer:

  • Why is the titration curve the shape that it is?
  • Where is the buffering region?
  • Do all titrations have the spike in the same place (no…the pH depends on the Ka/Kb of whatever is present in solution at the equivalence point and the volume where the spike occurs depends on the molarities of the acids and bases being mixed).
  • What species exist at each point on the curve?
  • How do you calculate pH for each point on a titration curve?

HW: Finish titration problems, cement your understanding of titration curves/ what we learned today.

Thursday: Indicator demo (blue food coloring and strong acids) + endpoint vs equivalence point and the relationship between indicator endpoint and its pKa.  We had a bit of extra time so I asked you to make up a titration question, but this wasn’t really clear since you hadn’t done one like that in a while. Will have to rethink it next year.

Friday: Review for Buffer/Titration test on Monday. Here’s the notes.

Week of 1/19

Monday: No school, MLK holiday

Tuesday: No school, Teacher workday

Wednesday: We finished the buffer exploration lab in which I asked you to measure how much acid and base it took to change the pH of an acetic acid solution by 2. Then do the same with a sodium acetate solution and then the same with a mixture of acetic acid and sodium acetate.  The results came up really well!

Lab write-up should include:

  • DN: lab notebook filled in properly,

  • DC: data collected along with procedure notes.

  • DP: presentation of data in an organized easy to interpret way and some statements of things you notice/ patterns / things that you thought were surprising / etc. Just think about your data.

  • C: Conclusion that is typed and submitted in google classroom. This should contain everything a normal conclusion contains, but will include much more theory as you explain your results in terms of buffer theory and perhaps less error analysis as you only did one trial of each.  You should comment on the validity as it relates to the theory.  If your results are unexplainable that indicates that something went awry and you should highlight that. Make sure to use data values to justify your claims and make sure to give a sense of the uncertainty in your measurements and conclusions.

Thursday: Lectured on lewis acids and had about 10 minutes to work on homework problems (See unit outline)

Friday: Lectured on buffers using these guided notes.  Here’s the class notes.

Week of 1/12/15

Monday: Review day number 2. We continued with this list of review questions and then you had a little time to work on problems from the textbook.

Tuesday: Test on Acids and Bases (part 1)

Wednesday: Salt hydrolysis lab and some notes on rules for salt hydrolysis. HW: read section in ch 16 on  salt hydrolysis.

Thursday: CA 47. HW finish CA 47 except for the last problem (calculation)

Friday: We started with a review of predicting acid/base for salt solutions. Then we went over the math for calculation of pH of salts.  Then we talked about what happens when you add strong acid or base to weak acid and weak base solutions and I pointed out that when you “neutralize” a weak acid with a strong base the resulting pH is not 7 because of the conjugate base that is left over.  The rest of class we worked on a lab to look at how adding strong acid and strong base changes the pH of weak acid and weak base solutions as well as a solution that is a mixture of both the weak acid and its conjugate base (acetic acid and sodium acetate).  Notes.

Week of 1/5/15

Monday: We started with a review of pH and pOH calculations and where it comes from (Self-Ionization of water). Then we did the chemactivity on definitions of acids and bases.  Note to self- PLEASE remember to change the definitions for arrhenius! They are confusing! Anyway, once nearly everyone made it through the identification of conjugate acids/bases we moved on to distinguish strong acids from weak.   A couple volunteers (Maddy and Amanda) measured the pH of a 1.0 M HCl and a 1.0 M HC2H3O2.  The predicted pH was 0, but only for HCl was it 0.  HC2H3O2 was greater than 0 indicating that it didn’t make as much H+ as it was supposed to…. this led into notes about strong vs. weak acids.  We ended w/ organic acids and amines definitions and symbols.   Notes.

Tuesday: Scary snow day. We had a somewhat shortened class with only 3 students absent, but went ahead anyway. We did pg 11-15 in the packet.  Homework is to get through page 15.  Page 16 is entirely optional. It’s just extra practice of some calculations we did on Monday.

Homework: Watch pH to pKa video here.

Wednesday: Short day b/c of a 2 hr delay.  We did some review (pg 9 and 10 of packet). Then you had time to practice pKa calculations.  Some of you watched the video b/c you had not yet done the hw.

Thursday: Super short b/c of 2 hr delay. So class was only 30 min.  We did this list of review questions.

Friday: Full class! Woo-hoo! I introduced the pKa lab and then you completed it.