Amphoteric: acid and/or base

[dana hu 1B]

Hello!
I'm a bit confused about how to tell if a substance can be an acid and a base and how it would bond with water as an acid and base. What are the main characteristics for a substance to be determined as an amphoteric?
Thank you!

[Yuelai Feng 3E]

Hi! In the Bronsted-Lowry definition, an acid is a proton donor and a base is a proton acceptor. In the Lewis definition, an acid is a electron acceptor and a base is an electron donor. (The Lewis definition has a wider range of application than Bronsted, but in many cases the Bronsted definition is useful.)

An amphoteric substance is a compound that can behave like an acid or a base, depending on the condition. I think the main types of amphoteric compounds we have encountered are:
(1) the diagonal band of amphoteric oxides (e.g. BeO, Al2O3, Ga2O3, ...)
(2) "amphiprotic" substances, which can donate or accept protons (e.g. HSO₄^-, H₂PO₄^-, HPO₄^2-...)

H2O is also amphoteric. It can donate a proton and become OH-, and it can accept a proton and become H3O+. When it reacts with acids, it behaves like a base; when it reacts with bases, it behaves like an acid.

Hope this answers your question!

[Samantha Lee 1A]

Amphoteric means that it can be both an acid or a base, depending on what the other molecule is in the reaction. One of the main examples is H2O. It can be either an acid or a base. If it is in a reaction with HCl, it would act as a base. If it was in a reaction with NaOH, water would act as the acid in this case. The only conditions to be an amphoteric molecule is that it has the ability to be an acid and a base (Needs electrons and H+ would be very good because it would allow the acid/base to be a lewis acid/base and a bronsted acid/base).

[Sabrina Galvan 3J]

H2PO4- is also another great example of an amphoteric molecule.
For a molecule to be amphoteric, it has to be able to donate an H+ ion (a Brønsted-Lowry acid), and it needs to be able to accept an H+(a Brønsted-Lowry base), so it must also carry a negative charge.

[Nick Saeedi 1I]

for a molecule to be amphoteric it needs to be able to act as a base or a acid so it needs to be a proton acceptor or a proton donor depending on what it reacts with. water is a good example as it can donate a hydrogen atom to become a hydroxide ion or accept an electron to become a hydronium ion.