How do I remove a stopper that has been stuck in the neck of a 100 mL round bottom flask since I forgot to wipe the neck of the flask. A salt was formed in the 100 mL flask and the stopper is just stuck like cement. Is there anyway to remove it without breaking the flask, breaking the stopper, or heating the flask (since I don't want to interfere with the product)?
Is it a hollow glas stopper?
Sometimes, it helps to hold the flask at the body and hit the corner of the lab bench with the stopper. If that doesn't help, heat the neck of the flask carefully with a heat gun.
Here is an alternative that worked like a charm for me. I have a wide-mouth lab jar with a thick, ground glass stopper that stuck tight. None of the other methods worked; oil, heat, tapping, etc. I had an aerosol spray used to blow dust from computer keyboards/screens (it is not compressed air but a liquid that becomes a gas as it is released - i.e. the can gets very cold as you use it). A quick shot of cold gas directly on the stopper and it immediately shrank enough to easily come out of the jar.
Another easy method is to get 2 other glass stoppers and tap them on both sides of the neck of the flask firmly, sometimes this will free it up immediately, other times you may need to have someone pulling the stopper while you hit the stoppers on the sides