The correct decreasing order of basic strength of the following species is _______.
H2O, NH3, OH–, NH2–
• Ammonia is more basic than water because NH3 has less electronegative central atom N (rather than O), therefore it’s tendency of holding onto electrons is much less than oxygen and it is better electron donor i.e. better base than H2O.
• When it comes to the basic strength order NH2– > OH –, conjugate acid-base pair concept must be taken into account i.e. the stronger the acid, the weaker will be the conjugate base.
• NH2– and OH – both of the species are the conjugate bases of NH3 and H2O respectively.
• As H2O is a stronger acid than NH3 (due to stronger proton donating ability of the former), H2O autoionizes itself but NH3 shows reluctance in donating protons.
• Therefore, conjugate base of water i.e. OH – must be a weaker base ( water is stronger acid)thanNH2– (as ammonia is weaker acid).
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