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On the other hand, if a chemical is a weak acid its conjugate base will not necessarily be strong. Consider that ethanoate, the conjugate base of ethanoic acid, has a base splitting constant (Kb) of about 5.6 × 10 −10, making it a weak base. In order for a species to have a strong conjugate base it has to be a very weak acid, like water.
It is the conjugate base of the hydrogencarbonate (bicarbonate) [8] ion, HCO − 3, which is the conjugate base of H 2 CO 3, carbonic acid. The Lewis structure of the carbonate ion has two (long) single bonds to negative oxygen atoms, and one short double bond to a neutral oxygen atom.
It is isoelectronic with nitric acid HNO 3. The bicarbonate ion carries a negative one formal charge and is an amphiprotic species which has both acidic and basic properties. It is both the conjugate base of carbonic acid H 2 CO 3; and the conjugate acid of CO 2− 3, the carbonate ion, as shown by these equilibrium reactions: CO 2− 3 + 2 H 2 ...
Another possibility is the molecular autoionization reaction between two water molecules, in which one water molecule acts as an acid and another as a base. H 2 O + H 2 O ↽ − − ⇀ H 3 O + + OH − {\displaystyle {\ce {H2O + H2O <=> H3O+ + OH-}}}
Another example of an amphoteric molecule is the bicarbonate ion HCO − 3 that is the conjugate base of the carbonic acid molecule H2CO3 in the equilibrium + + + but also the conjugate acid of the carbonate ion CO 2− 3 in (the reverse of) the equilibrium
As with any buffer system, the pH is balanced by the presence of both a weak acid (for example, H 2 CO 3) and its conjugate base (for example, HCO − 3) so that any excess acid or base introduced to the system is neutralized. Failure of this system to function properly results in acid-base imbalance, such as acidemia (pH < 7.35) and alkalemia ...
The protonation of water by sulfuric acid: H 2 SO 4 + H 2 O ⇌ H 3 O + + HSO − 4; The protonation of isobutene in the formation of a carbocation: (CH 3) 2 C=CH 2 + HBF 4 ⇌ (CH 3) 3 C + + BF − 4; The protonation of ammonia in the formation of ammonium chloride from ammonia and hydrogen chloride: NH 3 + HCl → NH 4 Cl
For example, acetic acid is a weak acid which has a = 1.75 x 10 −5. Its conjugate base is the acetate ion with K b = 10 −14 /K a = 5.7 x 10 −10 (from the relationship K a × K b = 10 −14), which certainly does not correspond to a strong base. The conjugate of a weak acid is often a weak base and vice versa.