You have to prepare a pH = 5.00 buffer, and you have the following 0.10 M solutions available: HCOOH, HCOONa, CH3COOH, CH3COONa, HCN, and NaCN. How many milliliters of each solution would you use to make approximately 1 L of the buffer?

검증된 단계별 안내

insert step 1> Identify the appropriate acid-base pair for the buffer. Since you need a pH of 5.00, choose the acid with a pKa close to 5.00. Compare the pKa values of HCOOH, CH3COOH, and HCN to find the best match.

insert step 2> Use the Henderson-Hasselbalch equation: \( \text{pH} = \text{pKa} + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) \). Substitute the desired pH and the pKa of the chosen acid to find the ratio \( \frac{[\text{A}^-]}{[\text{HA}]} \).

insert step 3> Calculate the concentrations of the acid (HA) and its conjugate base (A-) needed to achieve the desired pH. Use the ratio from the Henderson-Hasselbalch equation and the fact that the total concentration of the buffer components should be approximately 0.10 M.

insert step 4> Determine the volumes of the acid and conjugate base solutions required to achieve the calculated concentrations. Use the formula \( C_1V_1 = C_2V_2 \) to find the volumes, where \( C_1 \) and \( C_2 \) are the initial and final concentrations, and \( V_1 \) and \( V_2 \) are the initial and final volumes.

insert step 5> Adjust the volumes calculated in the previous step to ensure the total volume of the buffer solution is approximately 1 L. Verify that the pH is close to 5.00 using the Henderson-Hasselbalch equation.

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Buffer Solutions

A buffer solution is a system that resists changes in pH upon the addition of small amounts of acid or base. It typically consists of a weak acid and its conjugate base or a weak base and its conjugate acid. In this case, the pH of 5.00 indicates the need for a weak acid and its salt to maintain the desired acidity.

Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation relates the pH of a buffer solution to the concentration of its acid and conjugate base. It is expressed as pH = pKa + log([A-]/[HA]), where pKa is the acid dissociation constant. This equation is essential for calculating the required ratios of the weak acid and its salt to achieve the target pH.

Concentration and Dilution

Concentration refers to the amount of solute present in a given volume of solution, typically expressed in molarity (M). When preparing a buffer, understanding how to mix different concentrations and volumes of solutions is crucial to achieve the desired final concentration in the buffer. This involves calculating the volumes of the available solutions needed to reach 1 L of the buffer at pH 5.00.