Recently, I have got a compound which was dissolving in 1M NaOH. When I use 0.5 M H2SO4 to neutralize the supernatant, I found the liquid would precipitate and following add acid would lead to the dissolution of the precipitate. I thought this phenomenon was quite interesting worthy to share. May I have your advice on the potential compounds it could be? In the system, no metals beyond Na+, protein (amino acid) might exert these properties. How about others? Some polymers with what structures could also exert this property? If a polymer is an amphoteric electrolyte, it must contain amino group？ Just wanna talk about it and enrich my knowledge from you chemist. Thank you so much for your help and reply.

Regards

Xinxing