A Brownsted-Lowry base is a chemical that accepts a hydrogen ion `(H^+)`, while a Brownsted-Lowry acid is a chemical that accepts a hydrogen ion `(H^+)` . A substance can act as either a base or an acid depending on whether it accepts a proton or releases one. Thus, the same substance can act as Brownsted-Lowry base and acid in different reactions. Water is one such substance. When it reacts with hydrochloric acid, it works as a base, as seen in the following reactions:
Lowry-Brownsted Acid: `HCl -> H^+ + Cl^-`
Lowry-Brownsted Base: `H_2O + H^+ -> H_3O^+`
When water reacts with bicarbonate ion, it works as an acid.
Lowry-Brownsted Acid: `H_2O -> H^+ + OH^-`
Lowry-Brownsted Base: `HCO_3^-() + H^+ -> H_2CO_3`
Hence water can act as both a Lowry-Brownsted base and an acid.
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