4. Acid-Base Reactions

Amphoterism of Water

Water is amphoteric, which means it can act as either an acid or a base. In the reaction between acetic acid, CH3CO2H, and water, H2O, water acts as a base. The acetate ion CH3CO2 is the conjugate base of acetic acid, and the hydronium ion H3Ois the conjugate acid of the base, water:


Water can also act as an acid, as when it reacts with ammonia. The equation given for this reaction is:

H2O + NH3 ⇌ OH + NH4+

Here, H2O donates a proton to NH3. The hydroxide ion is the conjugate base of water, which acts as an acid, and the ammonium ion is the conjugate acid of the base, ammonia.

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