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.