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CHAPTER 3 75 
 
(b) According to Table 3.1, (CH3)3COH has a pKa of 18, 
while water has a pKa of 15.7. Water is more acidic 
because it has a lower pKa value. 
(c) According to Table 3.1, ammonia (NH3) has a pKa of 
38, while acetylene (H–C≡C–H) has a pKa of 25. As 
such, the latter is more acidic because it has a lower pKa 
value. 
(d) According to Table 3.1, H3O+ has a pKa of -1.7, 
while HCl has a pKa of -7. As such, the latter is more 
acidic because it has a lower pKa value. 
(e) According to Table 3.1, ethane (C2H6) has a pKa of 
50, while acetylene (H–C≡C–H) has a pKa of 25. As 
such, the latter is more acidic because it has a lower pKa 
value. 
(f) According to Table 3.1, a protonated ketone (the first 
structure shown) has a pKa of -7.3, while sulfuric acid 
(H2SO4) has a pKa of -9. As such, the latter is more 
acidic because it has a lower pKa value. 
 
 
3.5. According to Table 3.1, the proton connected to the 
oxygen atom is expected to be the most acidic proton in 
the compound. That proton is expected to have a pKa 
value near 16 (similar to CH3CH2OH). The proton 
connected to the nitrogen atom is expected to have a pKa 
value near 38 (similar to NH3). 
 
 
 
3.6. According to Table 3.1, the proton of the carboxylic 
acid group (Ha below) is expected to be the most acidic 
(pKa ~ 5). The two protons labeled Hb and Hc are 
expected to have a pKa near 10 (like C6H5OH), and the 
protons labeled Hd are expected to have a pKa near 38 
(like NH3). The order of acidity is shown below: 
 
 
3.7. 
(a) We first imagine protonating each base, and then we 
compare the pKa values of the resulting compounds 
(using Table 3.1): 
H
N
H
H
H C C H
pKa = 25
pKa = 38 
 
The first compound is more acidic because it has a lower 
pKa value. As a result, the conjugate base of the first 
compound will be a weaker base than the conjugate base 
of the second compound: 
 
 
 
(b) We first imagine protonating each base, and then we 
compare the pKa values of the resulting compounds 
(using Table 3.1): 
 
 
 
The latter compound is more acidic because it has a 
lower pKa value. As a result, the conjugate base of the 
latter compound will be a weaker base than the conjugate 
base of the former compound: 
 
 
 
(c) We first imagine protonating each base, and then we 
compare the pKa values of the resulting ions (using Table 
3.1): 
 
 
The former is more acidic because it has a lower pKa 
value. As a result, the conjugate base of the former will 
be a weaker base than the conjugate base of the latter: 
 
 
 
(d) We first imagine protonating each base, and then we 
compare the pKa values of the resulting compounds 
(using Table 3.1): 
 
 
 
The former compound (water) is more acidic because it 
has a lower pKa value. As a result, the conjugate base of 
the latter compound will be a stronger base than the 
conjugate base of water: 
 
 
 
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