Ephedrine, a central nervous system stimulant, is used in nasal sprays as a decongestant. This compound is a weak organic base:
C10H15ON (aq) + H2O (l) -> C10H15ONH+ (aq) + OH- (aq)
A 0.035 M solution of ephedrine has a pH of 11.33.
a) What are the equilibrium concentrations of C10H15ON, C10H15ONH<span>+, and OH-</span>?
b) Calculate <span>Kb</span> for ephedrine.
c(C₁₀H₁₅NO) = 0,035 M.<span>
pH = 11,33.
pOH = 14 - 11,33 = 2,67.
[OH</span>⁻] =
10∧(-2,67) = 0,00213 M.<span>
[OH</span>⁻] =
[C₁₀H₁₅NOH⁺] = 0,00213 M.<span>
[</span>C₁₀H₁₅NO] = 0,035 M - 0,00213 M = 0,03287 M.<span>
Kb = [OH</span>⁻] ·
[C₁₀H₁₅NOH⁺] / [C₁₀H₁₅NO].<span>
Kb = (</span>0,00213 M)² / 0,03287 M = 1,38·10⁻⁴.
