As chemistry issue

...Why would an exam board set questions on topics you haven't learnt?

Sometimes they ask questions about a molecule you've never heard of before eg there was a question on epoxyethane a few years ago. If you revise properly and learn everything in the specification you should be able to answer the question. You're not meant to know about it but should be able to think outside the box and relate it to your current knowledge.

Not really topics we haven't learnt but something a little outside the box that isn't clearly stated on the specification.

Like application of knowledge? Of course that's going to be on the exam, they want to make sure you actually know the theory, not just make you recite memorised phrases.