Water acts as a Bronsted acid as well as a Bronsted base. Give one example each to illustrate this statement.

You are correct; water can act both as a Bronsted acid and a Bronsted base, depending on the reaction it participates in. Let's illustrate this with one example for each:

Water as a Bronsted Acid:
When water donates a proton (H+) to another substance, it acts as a Bronsted acid. One classic example is its reaction with ammonia (NH3) to form ammonium ion (NH4+):
NH3 + H2O ⇌ NH4+ + OH-

In this reaction, water (H2O) donates a proton (H+) to ammonia (NH3), resulting in the formation of the ammonium ion (NH4+). Water loses a proton in this process, making it a Bronsted acid.

Water as a Bronsted Base:
When water accepts a proton (H+) from another substance, it acts as a Bronsted base. A common example is its reaction with hydrogen chloride (HCl):
HCl + H2O ⇌ Cl- + H3O+

In this reaction, water (H2O) accepts a proton (H+) from hydrogen chloride (HCl), forming the hydronium ion (H3O+). Water gains a proton in this process, making it a Bronsted base.

These examples show how water can display both acidic and basic behavior in different chemical reactions.