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| Conjugate Acid - Base Pair |
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| An acid after losing a proton becomes a base whereas a base after accepting the proton becomes an acid. |
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| For example, let us consider the reaction between water and ammonia as represented by the following equilibrium: |
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| In the forward reaction water acts as an acid and donates a proton to ammonia (base). In the reverse reaction ammonium ions (NH4+) act as acid and donate a proton to hydroxyl ions, OH- that act as bases. |
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| The base formed by the loss of proton by an acid is called conjugate base of that acid whereas an acid formed by gain of a proton by a base is called conjugate acid of the base. In the above example, OH- is the conjugate base of H2O and NH4+ is the conjugate acid of NH3. Acid - base pairs such as H2O/OH- and NH4+/NH3 which are formed by loss or gain of a proton are called conjugate acid - base pairs. |
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| Water (H2O) acts as both acid and base and such substances are called as amphoteric substances. |
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Rate of Chemical Reaction-Equilibrium
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