acid/base questions thread

[hypo]

Hey

why isnt H3PO4 amphiprotic? it can accept and donate a proton

also can someone please explain the strength vs concentration
 this question struck me

8 Consider the following solutions.
i 6 M hydrochloric acid
ii 0.1 M carbonic acid
iii 0.1 M nitric acid
iv 6 M ethanoic acid
Identify which solution represents:
a a dilute strong acid
b a concentrated strong acid
c a dilute weak acid

thanks
d a concentrated weak acid

[Mao]

H3PO4 is a polyprotic acid, it cannot accept a proton. Its anions, H2PO4- and HPO42-, however, are amphoteric.

Strong acids: HCl (hydrochloric), H2SO4 (sulfuric), HI (hydriodic), HNO3 (nitric)
Weak acids: H2CO3, CH3COOH, HF, C6H5COOH, [the list goes on and on)

Concentrated: usually greater than 1M
Dilute: usually less than 0.1M


Edit: typo