Question

Use Table 7.3 to help answer the following questions.

a. Which is the stronger base, ClO₄^-or C₆H₅NH₂?

b. Which is the stronger base, H₂O or C₆H₅NH₂?

c. Which is the stronger base, OH^- or C₆H₅NH₂?

d. Which is the stronger base, C₆H₅NH₂ or CH₃NH₂?

Short answer

Order of basic strength is given as:

(a) C₆H₅NH₂> ClO₄^-

(b) C₆H₅NH₂ > H₂O

(c) OH^- > C₆H₅NH₂

(d) CH₃NH₂ > C₆H₅NH₂

Step-by-step solution

Comparison of ClO4- and C6H5NH2

Strong acids give weak bases, as HClO₄ is strong acid hence its conjugate base i.e., ClO₄^- is weak base. C₆H₅NH₂ is stronger base as compared to ClO₄^-.

Comparison of H2O and C6H5NH2

C₆H₅NH₂ is a stronger base than H₂O because the K_b of H₂O is smaller than the K_b of C₆H₅NH₂.

Base	Formula	Conjugate Acid	Kb
Pyridine	C6H5NH2	C6H5NH3+	3.8×10-10

Comparison of OH- and C6H5NH2

OH^- is stronger because the K_b for OH^- (1.85 × 10^-5)is higher than the K_b of C₆H₅NH₂.

Comparison of C6H5NH2 and CH3NH2

K_bvalues for both of these are given in table 7.3 as:

Base	Formula	Conjugate Acid	Kb
Pyridine	C6H5NH2	C6H5NH3+	3.8×10-10
Methyl amine	CH3NH2	CH3NH3+	4.38×10-4

Higher the K_bvalue, higher will be basic strength, Hence CH₃NH₂is more basicthan C₆H₅NH₂.