Nice idea to create a game around math questions. The jump from easy to medium is quite high :). I have a degree in chemistry and had to think quite a bit to solve the questions :D. However I had my education quite some years ago and do not need much chemical knowledge in my daily job anymore. For someone who did not work in a job related to chemistry I think the medium questions are pretty hard. When I replayed some stages I saw that the same questions pop up, so I would recommend to add more questions for more variety.
Congratulations to this brain wrecking game :D and showing me how much of my chemistry knowledge vanished over the years :P.