When is the actual exam? One of the issues I had with revising AS chemistry last year is that there isn't a huge number of papers available, so personally I wouldn't advise doing them in February. In my opinion past papers are often misused, a lot of people seem to use them as a substitute for learning all of the content thoroughly and to a high level. This is a very risky strategy, because while you may understand and know the answers to the typical questions, it doesn't give you a lot of scope for adapting to whatever question they can ask you. I would highly recommend that you leave the past papers alone for now, and instead focus purely on the content for the time being. What I did last year was to get a large ring binder and I then printed out the part of the specification relevant to each topic (so for example I would print out the what you need to know section for say organic chemistry) and I would then make detailed notes from mainly chemguide, with chemrevise and the textbook for more specification specific topics. Doing this took me a long time (I started probably a week before easter holidays, took me 3-4 weeks to complete) as I made roughly 150 pages of notes. The act of doing this both ingrained the knowledge in my head as well as essentially giving me a personalised revision guide to look at. Only once I knew every bit of content did I then move onto the past papers, and this meant that rather than me learning the specific answer to the questions they asked I was able to answer almost every question they asked, and I then just had to refine my answers so that instead of getting say 2/3 i would get 3/3. Anyway hope this helped somewhat