I know that the OP was 2009 but I'm sure people will still find the tips on this thread useful so I'll post anyway. (*coughs* Not to mention I typed it up before realising the original date.) After getting a 5 in my Easter mock, I slaved away at Chemistry and got a 7. Here's what I did.
First of all, go through all of your old notes and try and rewrite them in a shortened format. This will refresh your memory of everything that you've learnt in the past year.
Having done that, get out the IB chemistry syllabus and go through all of the points (for the topics you've covered already). Get out a fresh piece of paper for each topic. The syllabus will say things like 'define what a lewis acid and base are' and at the top of each paper, write down all of the definitions for that topic. Then, by working through your shortened notes and the textbook, make sure you write down information on each point of the syllabus. This means you'll have a set of papers for each topic, with definitions, and by checking the syllabus, you can also see what you may have forgotten or not learnt over the past year.
Wait a few days then look back at this new set of notes. What are the difficult, hard to learn or easy to forget points within each topic? Is there a definition you know you'll struggle with or are you bad at remembering some examples of catalysts used in industrial work? Write down questions and make an answer sheet. For example, 'Name three radioisotopes and their uses' or 'what are the stages in a mass spectrometer?'. Try every day, or every other day, to answer, say, 5-10 of these questions and then check them. If you get one wrong, write down the correct answer and redo it with the next set of questions. Once you start getting the hang of them, answer the questions every week instead, or every fortnight. You'll still be refreshing your memory but it won't feel quite as repetitive.
Exam technique and past papers: At first, I didn't have the right exam techniques for how I answered questions. The papers we did within class whenever we finished a topic were used for A-Level as well so the way we answered questions was slightly different to what the IB wanted. It's harder when you've only covered half of the syllabus so far but find an old exam paper with an answer booklet and find a long question from a topic which you know you've covered already. Answer it without using your notes then look at the answer booklet and see exactly what it is you did wrong. Is your understanding of the theory wrong, are you missing out key points in your explanation or is it that you aren't answering them in the specific way that IB wants? An example of one I tended to mess up every time: 'which, out of X and Y, has a higher ionisation energy and why?' I had a habit of writing 'X has one more shell than Y so it...' instead of 'X has 3 shells and Y has two shells so...' and the answer booklet wanted me to be specific.
Don't do all of the exam papers you find, however. Your school may want to use the most recent ones for your mock exams and it's a bad idea to have covered them already because you will get an unrealistic idea of what you know and how you work under exam conditions if you've done the paper beforehand. You will also want to leave some exam papers for youself (idk, don't do any November papers or something) so that, when it gets to your revision period before the final exams, you also have some untouched papers you can do under timed conditions. When it reaches that point, practise doing the full exam. Time yourself doing all of Section A and two questions from Section B. Mark it and see what you've got. Then you should do the other two questions in the Section B, even if you hate the topics and mark those. You don't know what might turn up in your final paper so you need to cover all your bases. Similar questions will pop up again and again over the years. Sometimes when I practised, I found that I got higher marks in the topics I disliked than the ones I made a beeline for. I learnt how to look at the questions and really think about how much I knew I could answer instead of think about which question I simply had a personal preference for.
When it comes to the final exam, take deep breaths and try to remain calm. If you don't know a question in Section A, don't panic. Just leave it and do the rest of the paper. Then go back through the paper and cover the bits you left blank. This way you've answered all the bits you knew and you may have remembered it in answering another part.
Good luck to everyone!