According to the Bronsted Lowry definition,which can function both as an acid AND as a base?

Question

1. Cl-

2. SO4 2-

3. NH4+

4. HCO3-

5. H3O+

how do you know if it donates or accepts protons from the water if you don't know what the products are??? (if you write out the equation)

Answer 1

Answer is: 4. HCO3- (bicarbonate ion)

Acting as acid: HCO3- → CO3-- + H+

Acting as base: HCO3- + H+ → H2CO3

If a material has no hydrogens to donate, it can't be a Bronsted Lowry acid. Just about any material with a negative charge can be a Bronsted Lowry base. Cl- is a Bronsted Lowry base, although admittedly a very weak one. A neutral molecule with a lone pair of electrons act as Bronsted Lowry base, such as ammonia, H3N:.