One of the best things I ever did before taking my preliminary oral exam was to read my freshman chemistry book and solve all the problems in it. Surprisingly, I had never done that before. It was/is a good book, and covered a lot of stuff I had "learned for the test" and forgotten. And it was basic enough that I could read and follow along, mostly. I got asked several thermo questions and managed, though if you get the first question right, they then ask a tougher one, and then tougher, until you don't know, and then they give hints to see how well you think.
I don't think my boss expected me to pass, the pass rate was about 50%.
