What is the pH of a 0.20 M solution of the weak base ephedrine ( K _b = 1.4×10^{- 4})?

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Quizplus · Accepted Answer

Ephedrine is a weak base, so its pH can be calculated using the formula $pH = 14 - pOH$, where $pOH = -\log[\text{OH}^-]$. The concentration of $\text{OH}^-$ can be found using the $K_b$ expression, $K_b = \frac{[\text{Ephedrine}^+][\text{OH}^-]}{[\text{Ephedrine}]}$. Given $K_b = 1.4 \times 10^{-4}$ and the initial concentration of ephedrine, we can solve for $[\text{OH}^-]$ and subsequently find $pOH$, then $pH$. The calculation confirms that the pH is around 11.72, indicating a basic solution.

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