Although the acid-dissociation constant for phenol(C 6 H 5 OH) is 1.3 x 10 -10 .

Question

Although the acid-dissociation constant for phenol(C6H5OH) is 1.3 x 10-10. Thebase-dissociation constant for the phenolate ion(C6H5O-) is not.
A) Explain why it is not necessary to list both Ka forphenol and Kb for the phenolate ion? B) Calculate the Kb for the phenolate ion C) Is the phenolate ion a weaker or stronger base thanammonia Although the acid-dissociation constant for phenol(C6H5OH) is 1.3 x 10-10. Thebase-dissociation constant for the phenolate ion(C6H5O-) is not.
A) Explain why it is not necessary to list both Ka forphenol and Kb for the phenolate ion? B) Calculate the Kb for the phenolate ion C) Is the phenolate ion a weaker or stronger base thanammonia

Explanation / Answer

   given below, and therefore, anyone can be calculated fromthe other :       Ka x Kb = Kw , whereKw - ionic product of water = 1.0 x 10-14 at25o C    B) From the formula given above, Kb =1.0x10-14 / 1.3x10-10 = 7.69 x10-15
      Therefore, the value of Kb is 7.69 x10-15        C) In phenolate ion, due to the presence of negative charge onthe oxygen atom, it has 3 lone pairs of electrons, outof        which it partially donates 1 pair to the phenyl ring, dueto resonance. On the other hand, in ammonia, the nitrogenatom        has only 1 lone pair of electrons. Therefore, phenolateion is a better base as compared to ammonia.       Ka x Kb = Kw , whereKw - ionic product of water = 1.0 x 10-14 at25o C    B) From the formula given above, Kb =1.0x10-14 / 1.3x10-10 = 7.69 x10-15
      Therefore, the value of Kb is 7.69 x10-15        C) In phenolate ion, due to the presence of negative charge onthe oxygen atom, it has 3 lone pairs of electrons, outof        which it partially donates 1 pair to the phenyl ring, dueto resonance. On the other hand, in ammonia, the nitrogenatom        has only 1 lone pair of electrons. Therefore, phenolateion is a better base as compared to ammonia.       Therefore, the value of Kb is 7.69 x10-15        C) In phenolate ion, due to the presence of negative charge onthe oxygen atom, it has 3 lone pairs of electrons, outof        which it partially donates 1 pair to the phenyl ring, dueto resonance. On the other hand, in ammonia, the nitrogenatom        has only 1 lone pair of electrons. Therefore, phenolateion is a better base as compared to ammonia.        C) In phenolate ion, due to the presence of negative charge onthe oxygen atom, it has 3 lone pairs of electrons, outof        which it partially donates 1 pair to the phenyl ring, dueto resonance. On the other hand, in ammonia, the nitrogenatom        has only 1 lone pair of electrons. Therefore, phenolateion is a better base as compared to ammonia.

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