Calculate the ratio of CH3NH2 to CH3NH3Cl concentration required to create a buffer with pH=10.34.

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Identify the components of the buffer: CH3NH2 (a weak base) and CH3NH3Cl (its conjugate acid).

Use the Henderson-Hasselbalch equation for a buffer solution: \( \text{pH} = \text{pK}_a + \log \left( \frac{[\text{Base}]}{[\text{Acid}]} \right) \).

Find the \( \text{pK}_a \) of CH3NH3Cl. Since \( \text{pK}_a + \text{pK}_b = 14 \), calculate \( \text{pK}_a \) using the \( \text{pK}_b \) of CH3NH2.

Substitute the given pH (10.34) and the calculated \( \text{pK}_a \) into the Henderson-Hasselbalch equation.

Solve for the ratio \( \frac{[\text{CH}_3\text{NH}_2]}{[\text{CH}_3\text{NH}_3\text{Cl}]} \) using the equation.

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주요 개념

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Buffer Solutions

Buffer solutions are mixtures that resist changes in pH when small amounts of acid or base are added. They typically consist of a weak acid and its conjugate base or a weak base and its conjugate acid. In this case, CH3NH2 (methylamine) acts as the weak base, while CH3NH3Cl (methylammonium chloride) serves as its conjugate acid.

Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation is a mathematical formula used to calculate the pH of a buffer solution. It is expressed as pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the base and [HA] is the concentration of the acid. This equation allows for the determination of the required ratio of base to acid to achieve a desired pH.

pKa and pH Relationship

The pKa is the negative logarithm of the acid dissociation constant (Ka) and indicates the strength of an acid in solution. The relationship between pKa and pH is crucial for buffer calculations, as it helps determine how much of the acid and base components are needed to achieve a specific pH. For a buffer to be effective, the pH should be close to the pKa of the weak acid or base involved.