It’s continuous learning. I mean, what I used to try to say to students when I taught the acid-base stuff I’d say ‘look there are only about six types of problems and if you can solve one of them you can solve them all because they’re all the same.’ But what you’ve got to be able to do is look at the question and say to yourself ‘this is one of those types of questions therefore this is the way I should think about approaching it.’ So take the question, dissect it, decide what you’re being asked to do, decide what information you’re given, and then say ‘yeah that’s one of those types of q
We teach way too much stuff. We teach way too much stuff that we used to teach because students didn’t have the resources available to them that they’ve got now. I mean if you look at the resources - they’ve got textbooks, they’ve got electronic media, they’ve got Sapling. They can do the problems in their own time in a guided way with something like Sapling.
Students from high school might understand that vinegar for example is a weak acid compared to hydrochloric acid, but they never knew why. And you could then show them that with equilibrium, this is why. And all of a sudden they’re, 'oh, I’ve always known that I shouldn’t spill HCL on my hand, but I can spill vinegar on my hand and put it on my fish and chips'... Those sorts of moments can really... the students go ‘oh wow.’
If you look at the resources - students’ have textbooks, they have electronic media, they have Sapling. They can do the problems in their own time in a guided way with something like Sapling. All we as lecturers have to do is give them the framework to solve the problems. If you set up the framework for them and let them go away and use that framework and learn how to solve problems they’ll teach themselves. So it’s a matter of giving them that framework and it’s the buffers that are the framework of it all.
Link this topic to organic reactions since a lot of them are actually acid/base reactions. That is, there is one species that’s electron rich and one that’s electron poor.
Start with HA and move on to specific chemistry. Reinforce pKa and connect with buffers by asking students to pick conjugate acid/base combinations to make up buffers with different pH. Use the concept that adding strong acid to a buffer converts it to a weak acid, increasing the overall concentration of weak acid.
There are only about three key principles that they need to know from this topic at first year level. All of it comes back to understanding equilibrium and buffers. Because if they understand buffers (which involves understanding weak acids and weak bases, conjugate acids, conjugate bases, equilibrium, Ka, Kb) then they can immediately understand titrations and all the concepts that they need because they’re encompassed in the concept of a buffer. If they’re dealing with either biological or chemical systems they’ll deal with buffers.
Use drugs as an example of the relationship between how much of a species is protonated and how much is non-protonated. This is an equilibrium process. For a carboxylic acid drug, if it’s protonated it’s not ionic, if it’s not protonated it’s anionic. And if it’s going from gut into blood for example, whether or not it goes through the membrane will depend upon the pH of the system.
Ask the students to look at structures and consider what charge different parts of the molecules will have when they are protonated and deprotonated (eg. COOH to COO- is neutral to negative, and NH3+ to NH2 is positive to neutral, but can have OH groups that become O- sometimes, depending on the pKa). Use a table of amino acid structures and pKa values, and get them to work out charges at the pH of interest.
