Question

Give equations showing how the following molecules and ions may act as bases:

CO2-, H2O, SO4-, NH3, HCO2-

Answer 1

Water is amphoteric: this means that it can act both as an acid and as a base. The reason for this is that water is self-ionising. 

2H2O⇌H3O^+ + OH^-

The sulfate ion (SO4-) is basically called conjugate base of sulphuric acid, after releasing two H+ ions in polar medium like water.

NH3 (Lewis base ) donates lone pair to vacant p orbital of BF3 (Lewis acid) to form adduct.