[john !!]

Can someone give me a good A-level (edexcel?) defenition for amphoteric?
I don't think I know, but it keeps coming up in the periodic table II. thanks

and can someone also check that silicon dioxide (sand) is acidic and reacts with sodium hydroxide in this reaction:

SiO(2) + 2NaOH ---> Na(2)SiO(3) + H(2)O

Numbers in brackets mean subscript. I wrote this down either wrong or the teacher did, and it wasn't balanced at all so I did it just now, but it could still be wrong.

THanks a lot
Michael

[oxymoron]

An amphoteric substance is one that can act either as an acid or a base.

For example water (can gain a proton to from H(3)O+ or can lose a proton to form OH-)
Another example you may come across is Aluminium Oxide.

SiO2 is indeed acidic and does react with NaOH according to your equation (the salt is called sodium silicate).
Remember though the NaOH must be concentrated and hot as it is quite difficult to get SiO2 to react due to it's giant covalent structure.

[Angler fish]

It means that it possesses the properties of both an acid and a base, for example amino acids!

EDIT: I see someone posted the answer whilst I posted mine!