Question

Amphetamine (C9H13N) is a weak base with a pKb of 4.2.

Answer 1

Weak base: [OH⁻] = √Kb.C

pKb = 4.2

$\tt Kb=10^{-4.2}$

c = concentration

MM Amphetamine (C9H13N) = 135.21 g/mol

c = 215 mg/L = (0.215 g : 135,21 g/mol) / L = 0.00159 mol/L = 1.59  x 10⁻³ mol/L

$\tt [OH^-]=\sqrt{10^{-4.2}\times 1.59\times 10^{-3}}=3.17\times 10^{-4}$

pOH = 4 - log 3.17

pH = 14 - (4 - log 3.17)

pH = 10 + log 3.17 = 10.50