Normally colleges ask for a grade B or above, not exactly sure what that will equate to with the new 9-1 system, but somewhere likely around that mark. It's a shame you have to do a foundation paper if you want to go on to study chemistry further, you should talk to your teachers and see if you can be moved to higher tier. Whether or not a college will let you study chemistry with a grade 5, it will be a very big jump up to A level, as it is anyway, even for people who will have Grade A and above.