Chemistry is a course that requires WORK, as in completing questions.
The fundamental logic is that, the more type of questions that you complete, the more you are prepared for various exam/SAC questions. I could guarantee you, that your mark will reflect the amount of work you have put in.
So, to answer you question, a teacher is there to answer your queries, to explain concepts you may find difficult exploring on your own that lies behind the query.
However, when you are capable of self-studying, as in being able to solve problems on your own and grasping all the knowledge that involves, a teacher may nolonger be necessary for you.
But it certainly benefits you when you have a teacher who is excellent at explaining Chemistry in class, who doesn't want to have their knowledge re-inforced by a pro? =P