Tuesday: Review for AS and PT test with multiple choice practice test.
Wednesday: Test and organic naming of branched alkanes
Thursday: Branched alkenes and ionic vs covalent bonding. Using this packet. Also handed out pages from IB databook for trends in IE, EA, EN and melting points.
Friday: Functional groups and naming alcohols and carboxylic acids.
Week of Jan 21
Monday was MLK day so no school.
Tuesday was a teacher work day.
Wednesday: We reviewed periodic trends and applied Coulomb’s law to explain them. (Atomic radius, ionization energy, reactivity and electron affinity). The big difference between AP and first year is to be able to explain the exceptions. Homework was to read the dos and don’ts of periodic trends.
Thursday: We reviewed the wave mechanical model of the atom. I gave a bit of a history lesson (why we think electrons are waves, etc.) and then got into the details of orbital diagrams and electron configurations using this. Note for next year: I wanted to introduce quantum numbers right away, but it was much better to do this after students had reviewed s,p,d, f notation.
Friday: We learned quantum numbers and did several exercises in this, as well as some practice problems from chapter 7.
Week of Jan 14
Monday and Tuesday: work days, review days, time to ask me questions days. All block was spent working problems. I think next year I should go over some key concepts rather than just working problems. In the end the time spent doing homework didn’t result in strong ability to identify buffer systems. So next year we’ll do the multiple choice problems on the practice test together. I think I should also make a movie for some of the problems. The titration problem in the homework had the same volume base added as acid because they were the same concentrations. Because of this, students were tricked into thinking that it would always be the same.
salt hydrolysis reactions!!!
identifying buffer systems
knowing what happens when strong acid/base is added. Strong acid or base reacts completely. Handle that first.
does it matter whether you use Ka or Kb?
Thursday: Review of light, wave concepts and then Bohr Model lab done together as a class.
Friday: Spent most of the class going over the buffer test since it was such a challenge. Homework was to graph some ionization energy graphs. Get spreadsheet here.
Tuesday: Buffer Lab design day. First started with a warm-up asking students to identify buffer systems to show them that a buffer could be made with a weak acid and fewer moles of strong acid. This is important for their design labs. Basic buffers were hard for students. Sodium borate worked for pH 9 and sodium carbonate worked for pH 10. pH 7 using phosphates also worked well. pH 3-6 were a bit iffy. Not sure if the calculations were bad or what, but most groups needed to add either alot more of conjugate salt or sodium hydroxide to get desired pH.
Wednesday: Buffer lab day. Next year have out strong concentrations for changing pH and weak (0.1 or 0.05 M for titration purposes). Also, prepare to teach them how to calculate theoretical buffer capacity. It is not something they were able to figure out on their own.
How to calculate theoretical buffer capacity!
Start with original H-H equation with pKa or pKb filled in. Put in (original pH+2) to calculate the amount of base needed to change pH by 2 units.
Calculate ratio of acid to base. This is the ratio of acid to base you should have when the pH is 2 less than started. Example if ratio is 100 = Af/HAf, then 100 HAf = Af, where HAf = the moles of weak acid present after addition of x amount of moles of strong base (OH-) and Af = amount of moles of the conjugate base present after addition of x amount of moles of strong base.
We also know that the final moles of acid (HAf) will equal the initial moles of weak acid (HAi) – x because for everyone mole of OH- added, one mole of HA will react. Thus: HAf = HAi – x
And the final moles of the conjugate base (Af) will equal the initial moles of conjugate base (Ai) + x, because for every one mole of acid reacted, one mole of conjugate base is formed. Thus Af = Ai + x
Further, we know the initial moles of acid and base in the original buffer solution because we needed those to make the buffer in the first place! So for example, to make your buffer you might have used 0.01 moles of HA and 0.005 moles of A-. Now, taking into consideration that we only tested 20 mL, not the original 100 mL we should divide the initial moles by 5. (you can also solve the molarity equation if you didn’t use exactly 1/5 of the 100 mL solution).
So now we have HAi = .002 moles and Ai = .001 moles. Plug these numbers into the expressions found above (#3 &4) and plug those into the express in #2. Solve for x. X = moles of base added. You can then use the molarity of the base you used to solve for the number of mL of base that theoretically should have been handled by the buffer.
Now, do basically, but not exactly the same, for adding strong acid. Do not just SHOW your calculations but give the reasoning behind them as I have shown above. This is what I expect to see. Not just a bunch of numbers that I have to interpret, but a clearly written out expression of the assumptions and concepts behind the calculations.
Rubric for Conclusion:
4: Student clearly shows understanding of HOW to make a buffer and HOW a buffer works. Has evaluated the buffer’s ability to handle acid and base and related that to a) ratio and b) theoretical buffer capacity. Attempts to explain discrepancies.
3: Does not show understanding of HOW to make a buffer, but does show understanding of how it works by applying ratio qualitatively to amount of acid and base handled. If any additions of strong acid/base, student explains the effect this had. Attempts to explain discrepancies.
2: Summarizes what was done and the results, including any discrepancies, but does not connect results to ratio or theoretical buffer capacity.
Thursday: Started with indicator lab using buffers you made last class. Note to self: need picture so kids understand. Many didn’t get the idea of what we were trying to do. They thought we were trying to continue adding indicator until the color changed rather than find the pH. Possibly identify the variables more clearly (IV being the indicator and DV being the pH range of color change), but also need to have a picture so they understand. Use picture from phone. Next we went outside (cuz it was so nice). Attempted to do a simulation of a titration of a weak acid by giving them colored paper. Next time need to discuss the roles better. Such as, weak bases try to get protons, but self-regulate so no more than 1/2 of them have protons. Or something like that! Then I lectured on the pH at equivalence point for weak acid and base titration + how to calculate the actual pH. Being outdoors was cold (we were in the shade) and some distractions were going on so students did not fully understand this lesson and I ended up teaching it again in class, and on the following Monday/Tuesday when we spent time reviewing for the test.
Friday: Indicator notes – I presented on how the pH range for an indicator’s end point is determined and we finished the indicator worksheet we’d started yesterday.
Week of Jan 3
Only a 2 day week this week!
Thursday: we started the second half of the acids-bases unit with the Salt Hydrolysis lab (more of an exploration really) that showed how some salts that aren’t obviously acids or bases affect the pH of a solution as if they were acids or bases. Then you worked on CA 47 to get an equilibrium explanation for this behavior and learn to calculate pH for various salt solutions.