There are no required subjects for Law at Oxford - the only note about subject choice on the course page is "An essay subject can be helpful when completing this course but is not required for admission."
There are no secrets here - all Unis have to be entirely upfront and honest about their entry requirements, so Chemistry will not give you any advantage in itself, however 'analytical' you might think it is, but equally the fact that Chemistry and Biology are subjects not directly related to Law has no impact on your chances of an offer. And btw, Psychology is a solid academic subject and no University would ever regard it as 'soft'.
What is important, for all top Law courses, is three high grades. So logic suggests you should drop your weakest subject and focus on the other three.