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Conjugate Acids and Conjugate Bases

Key Questions

  • Answer:

    Here is one answer.


    See this Socratic answer.

    And here's another way to look at it.

    A conjugate acid contains one more H atom and one more + charge than the base that formed it.

    A conjugate base contains one less H atom and one more - charge than the acid that formed it.

    Let us take the example of bicarbonate ions reacting with water to create carbonic acid and hydronium ions.

    HCO₃⁻ + H₂O → H₂CO₃ + OH⁻
    base + acid → Conj A + Conj B

    We see that HCO₃⁻ becomes H₂CO₃. It has one more H atom and one more + charge (-1 + 1 = 0). So H₂CO₃ is the conjugate acid of HCO₃⁻.

    The H₂O becomes OH⁻. It has one less H atom and one more – charge. So OH⁻ is the conjugate base of H₂O.

  • Acid strength is determined by the amount of that acid that actually ionizes. Acids are molecular covalent compounds which you don't expect to ionize (release an #H^+# and leave behind the conjugate base, or #Cl^-# for example).

    The strongest acids ionize 100%. There are 6 that most consider to be the "STRONG" acids: HCl, HI, HBr, HNO_3#, H_2SO_4# and HClO_4#. These split apart 100%.

    All other acids are weak acids and ionize to a much lesser amount. For example, acetic acid, like most weak acids, ionizes, 5%.

  • All acids have a conjugate base. All bases have a conjugate acid. Acids "donate" #H^(+)# when they react. This is most easily seen when they dissociate in water:

    #H_2SO_4# + #H_2O# => #HSO_4^-# + #H_3O^+#

    In this example, sulfuric acid (#H_2SO_4#) is an acid because it "donates" #H^+# to the water. It becomes the hydrogen sulfite ion (#HSO_4^-#) which is the conjugate base of sulfuric acid.

    The same idea applies to a base:

    #NH_3# + #H_2O# <=> #NH_4^+# + #OH^-#

    Ammonia (#NH_3#) is a base because is "accepts #H^+# from water to come its conjugate acid, the ammonium ion (#NH_4^+#).

    This video gives an overview of acids and bases; the second half is about conjugate pairs:

    Simple, easy to understand can be on this site http://www.chemteam.info/AcidBase/Conjugate-Pairs.html