I just finished summarising Unit 4, so I thought I'd post up the summary here for anyone else who wants it. The summary is of Heinemann Chemistry 2, but includes a bit of other stuff from my teacher's notes in places. Admittedly, this is sort of a first draft and lacks a few diagrams and perhaps some clearer explanations at times, but it's a start.

The chapters covered are 15-18, 21 (sulfuric acid), and 23-28. Chapters 19, 20 and 22 are for other industrial chemicals I don't plan on writing about in the exam, so I haven't bothered taking the time to summarise them, too.
Please point out any mistakes (typographical or otherwise) so I can correct them. It would be much appreciated.