Which buffer system is the best choice to create a buffer with pH = 7.20? For the best system, calculate the ratio of the masses of the buffer components required to make the buffer: HC2H3O2/KC2H3O2, HClO2/KClO2, NH3/NH4Cl, or HClO/KClO.

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Identify the buffer systems and their corresponding weak acid and conjugate base pairs: HC_2H_3O_2/KC_2H_3O_2, HClO_2/KClO_2, NH_3/NH_4Cl, and HClO/KClO.

Use the Henderson-Hasselbalch equation: \( pH = pK_a + \log \left( \frac{[A^-]}{[HA]} \right) \) to determine which buffer system has a \( pK_a \) closest to the desired pH of 7.20.

Look up the \( pK_a \) values for each weak acid: \( pK_a \) of acetic acid (HC_2H_3O_2), chlorous acid (HClO_2), ammonia (NH_3), and hypochlorous acid (HClO).

Select the buffer system with a \( pK_a \) value closest to 7.20, as this will provide the most effective buffering capacity at the desired pH.

Once the best buffer system is identified, use the Henderson-Hasselbalch equation to calculate the ratio \( \frac{[A^-]}{[HA]} \) needed to achieve the pH of 7.20, and then convert this ratio to the ratio of masses of the buffer components.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Buffer Systems

A buffer system is a solution that resists changes in pH when small amounts of acid or base are added. It typically consists of a weak acid and its conjugate base or a weak base and its conjugate acid. The effectiveness of a buffer is determined by its pKa and the concentrations of its components, which help maintain the desired pH level.

Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation relates the pH of a buffer solution to the pKa of the acid and the ratio of the concentrations of the conjugate base to the weak acid. It is expressed as pH = pKa + log([A-]/[HA]). This equation is essential for calculating the required ratios of buffer components to achieve a specific 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. A lower pKa value means a stronger acid. Understanding the relationship between pKa and pH is crucial for selecting the appropriate buffer system, as the pH of the buffer should ideally be close to the pKa of the weak acid used.

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Textbook Question

Blood is buffered by carbonic acid and the bicarbonate ion. Normal blood plasma is 0.024 M in HCO₃^- and 0.0012 M H₂CO₃ (pK_a1 for H₂CO₃ at body temperature is 6.1).

c. Given the volume from part (b), what mass of NaOH can be neutralized before the pH rises above 7.8?

Textbook Question

The fluids within cells are buffered by H₂PO₄^- and HPO₄^2- . b. Could a buffer system employing H₃PO₄ as the weak acid and H₂PO₄^- as the weak base be used as a buffer system within cells? Explain.

Textbook Question

Which buffer system is the best choice to create a buffer with pH = 9.00? For the best system, calculate the ratio of the masses of the buffer components required to make the buffer. HF/KF HNO₂/KNO₂ NH₃/NH₄Cl HClO/KClO

Textbook Question

A 500.0-mL buffer solution is 0.100 M in HNO₂ and 0.150 M in KNO₂. Determine if each addition would exceed the capacity of the buffer to neutralize it. a. 250 mg NaOH

Textbook Question

A 500.0-mL buffer solution is 0.100 M in HNO₂ and 0.150 M in KNO₂. Determine if each addition would exceed the capacity of the buffer to neutralize it. b. 350 mg KOH