Question

Ephedrine, a central nervous system stimulant, is used in nasalsprays as a decongestant. this compound is a weak organic base: {\rm{c}}_{10} {\rm{h}}_{15} {\rm{on(}}aq{\rm{)}} + {\rm{h}}_2 {\rm{o}}(l{\rm{)}} \overrightarrow{\leftarrow} {\rm{c}}_{10} {\rm{h}}_{15} {\rm{onh}}^ + (aq) + {\rm{oh}}^ - (aq) a 0.035 {\rm m} solution of ephedrine has a{\rm ph} of 11.33. what is the equilibrium concentration of{\rm{c}}_{10} {\rm{h}}_{15} {\rm{on}}, {\rm{c}}_{10} {\rm{h}}_{15} {\rm{onh}}^ +, and oh-.

Answer 1

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+, and OH-?

b) Calculate Kb for ephedrine.

c(C₁₀H₁₅NO) = 0,035 M.
pH = 11,33.
pOH = 14 - 11,33 = 2,67.
[OH⁻] = 10∧(-2,67) = 0,00213 M.
[OH⁻] = [C₁₀H₁₅NOH⁺] = 0,00213 M.
[C₁₀H₁₅NO] = 0,035 M - 0,00213 M = 0,03287 M.
Kb = [OH⁻] · [C₁₀H₁₅NOH⁺] / [C₁₀H₁₅NO].
Kb = (0,00213 M)² / 0,03287 M = 1,38·10⁻⁴.