chapter5 - Chapter 5 5.2 Identify the conjugate bases of...

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Chapter 5 5.2 Identify the conjugate bases of the following acids: (a) [Co(NH 3 ) 5 (OH 2 )] 3+ ? A conjugate base is a species with one fewer proton than the parent acid. Therefore, the conjugate base in this case is [Co(NH 3 ) 5 (OH)] 2+ , (b) HSO 4 - ? The conjugate base is S0 4 2- . (c) CH 3 OH? The conjugate base is CH 3 0 - . (d) H 2 P0 4 - ? The conjugate base is HP0 4 2- . (e) Si(OH) 4 ? The conjugate base is SiO(OH) 3 . (f) HS - ? The conjugate base is S 2- . 5.3 Identify the conjugate acids of the following bases? (a) C 5 H 5 N (pyridine)? A conjugate acid is a species with one more proton than the parent base. Therefore, the conjugate acid in this case is the pyridinium ion, C 5 H 6 N + , shown below. (b) HP0 4 2- ? The conjugate acid is H 2 P0 4 - . (c) 0 2- ? The conjugate acid is OH-.
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(d) CH 3 COOH? The conjugate acid is CH 3 C(OH) 2 + shown above. (e) [Co(CO) 4 ]? The conjugate acid is HCo(CO) 4 , shown below. A drawing of the HCo(CO) 4 molecule, the conjugate acid of the tetrahedral Co(CO) 4 - anion. The C atoms of the CO ligands are bound to the Co atom. The O atoms are unshaded. (f) CN - ? The conjugate acid is HCN. 5.4 List the bases HS - , F - , I - , and NH 2 - in order of increasing proton affinity? You should make use of Table 5.1 to answer this question. The species with the greatest proton affinity will be the strongest base, and its conjugate acid will be the weakest acid. The weakest acid will have the smallest value of K a (or the most positive value of pK a ). Since Table 5.1 shows that HI is a stronger acid than HF which is a stronger acid than H 2 S, a partial order of proton affinity is I - <F - < HS - . Since NH 3 is a very weak acid, NH 2 - must be a very strong base. Therefore, our final list, in order of increasing proton affinity, is I - <F - < HS - <NH 2 - . 5.5 Which bases are too strong or too weak to be studied experimentally? (a) C0 3 2- , 0 2- , ClO 4 - , and N0 3 - in water? You can interpret the term “studied experimentally” to mean that the base in question exists in water (i.e. it is not completely protonated to its conjugate acid) and that the base in question can be partially protonated (i.e. it is not so weak that the strongest acid possible in water, H 3 0 + , will fail to produce a measurable amount of the conjugate acid). Using these criteria, the base C0 3 2- is of directly measurable base strength, since the equilibrium C0 3 2- + H 2 0 ? HC0 3 - + OH - produces measurable amounts of reactants and products. The base 0 2- , on the other hand, is completely protonated in water to produce OH-, so the oxide ion is too strong to be studied experimentally in water. The bases Cl0 4 - and N0 3 - are conjugate bases of very strong acids, which are completely deprotonated in water. Therefore, since it is not possible to protonate either perchlorate or nitrate ion in water, they are too weak to be studied experimentally. (b) HSO
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chapter5 - Chapter 5 5.2 Identify the conjugate bases of...

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