The ion HCO3–(aq) can act as an acid or a base in water. (a) Write the reaction for it acting as a base. (b) Write the reaction for it acting as an acid. ?

(a).

##HCO_(3(aq))^(-)+H_((aq))^+rarrH_2CO_(3(aq))##

(b).

##HCO_(3(aq))^(-)rarrCO_(3(aq))^(2-)+H_((aq))^(+)##

The Lowry Bronsted theory describes an acid as a proton donor and a base as a proton acceptor.

On this basis you can see in (a) it is acting as a base and in (b) it is acting as an acid.