I'm unsure about how much I need to know about the topic area I am applying for. It is related to my degree but I chose a lot of qualitative free choices rather than the straight science options, the PhD is a scientific course. I am good at the science aspect but I lack in chemistry knowledge and feel that this may make my application weaker. How much am I supposed to know about a topic I want to study in and is there scope to learn some of the background I may be lacking?Many thanks!!

This depends on what the general area of the PhD is. If it is a chemistry Phd then without good chemical theory you will find it very difficult to complete. However if it is in another area with some chemical applications or some minor chemical work needed then you will probably be ok if you work on your theory. Post more info and I will be able to give better advice - I am a chemist.