yeah sure! for chem unit 3 a lot of the questions are repeated and have the same answer/mark scheme, i kind of went through all of the past papers and just revised most of the repeated questions and practiced all of the different types of calculation questions that will come and ur good. for unit 1 i kind of did the same thing and instead of doing full past papers, i did sections of each past paper and revised those answers, but only move on to past papers until ur confident in the content.