Chapter 15.6, Problem 2RCF

Consider the following three solutions of equal concentration. Using data in Table 15.4, rank the three solutions from most basic to least basic: (a) aniline, (b) methylamine, (c) caffeine.

Table 15.4    Ionization Constants of Some Weak Bases and Their Conjugate Acids at 25°C

Name of Base	Formula	Structure	Kb*	Conjugate Acid	Ka
Ethylamine	C2H5NH2		5.6 × 10−4	${\text{C}}_2{\text{H}}_5\stackrel{+}{\text{N}}{\text{H}}_3$	1.8 × 10−11
Methylamine	CH3NH2		4.4 × 10−4	${\text{CH}}_3\stackrel{+}{\text{N}}{\text{H}}_3$	2.3 × 10−11
Ammonia	NH3		1.8 × 10−5	${\text{NH}}_4^{+}$	5.6 × 10−10
Pyridine	C5H5N		1.7 × 10−9	${\text{C}}_5{\text{H}}_5\stackrel{+}{\text{N}}\text{H}$	5.9 × 10−6
Aniline	C6Η5ΝΗ2		3.8 × 10−10	${\text{C}}_6{\text{H}}_5\stackrel{+}{\text{N}}{\text{H}}_3$	2.6 × 10−5
Caffeine	C8H10N4O2		5.3 × 10−14	${\text{C}}_8{\text{H}}_{11}{\stackrel{+}{\text{N}}}_4{\text{O}}_2$	0.19
Urea	(NH2)2CO		1.5 × 10−14	${\text{H}}_2\text{NCO}\stackrel{+}{\text{N}}{\text{H}}_3$	0.67