What is the molar ratio of salt/base required to prepare a...

What is the molar ratio of salt/base required to prepare a buffer of ephedrine and ephedrine hydrochloride having $\mathrm{pH}$ 8.8? The $\mathrm{pK}_{\mathrm{a}}$ of ephedrine is 9.36 at $25^{\circ} \mathrm{C}$.

Key Concepts

Logarithmic Relationships in Acid-Base Equilibria

The logarithmic relationship in the Henderson-Hasselbalch equation means that small differences in pH relative to the pKa can lead to exponential changes in the ratio of base to acid. This relationship is essential for accurately calculating the required molar ratio of constituents in buffer preparation.

pKa and pH

The pKa of an acid is a measure of its dissociation constant, reflecting its strength as a weak acid, while pH measures the hydrogen ion concentration in a solution. The difference between pH and pKa indicates the relative proportions of the conjugate acid and conjugate base in the buffer, which is pivotal when determining the buffer's composition.

Buffer Solutions

Buffer solutions resist changes in pH when small amounts of acid or base are added. They consist of a weak acid and its conjugate base or a weak base and its conjugate acid. Understanding how the components interact through equilibrium is crucial for designing buffers with specific pH levels.

Henderson-Hasselbalch Equation

This equation is fundamental for calculating the ratio of conjugate base to acid in a buffer solution. It is given by pH = pKa + log([Base]/[Acid]), and by rearranging this expression, one can determine the necessary molar ratio of salt (providing the conjugate acid form) to base to achieve a desired pH.

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