I saw as an example that water is amphoteric (to be more precise amphiprotic), and I came up with the following questions:
Is there any substance that acts as a weak acid and a strong bases at the same time, or vice versa?
If so, or if not so, please give some explanations on the possible reasoning using their structures.
Also I have another question which is quite related but too short to be posted as an independent question, so I will ask here. The necessary condition for a substance to be amphoteric, as I heard, is that for it should have a hydrogen atom in it, and also the molecule should either have a lone pair of electron or be negatively charged. I understand the conditions about hydrogen atom and an electron pair, but why can the negatively charged property possibly be a necessary condition for a molecule to be amphoteric?
Thanks in advance.