Henderson Hasselbalch Buffers and Volumes

In summary, the Henderson Hasselbalch equation is a mathematical formula used to calculate the pH of a buffer solution. Buffers maintain a stable pH by resisting changes when small amounts of acid or base are added. Factors such as the concentrations of the buffer components, solution volume, and temperature can affect the buffering capacity of a solution. Henderson Hasselbalch buffers can be prepared by mixing a weak acid with its conjugate base in a specific ratio, with the concentrations adjusted using the Henderson Hasselbalch equation. These buffers have various applications in laboratory experiments and medical settings, where maintaining a specific pH is crucial.
  • #1
Meadow_Lark
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Homework Statement



You have 725 mL of an 0.55 acetic acid solution. What volume (V) of 1.30 M NaOH solution must you add in order to prepare an acetate buffer of pH = 4.99? ( The pKa of acetic acid is 4.76.)
[/B]

Homework Equations



pH = pKa + log A/HA
Ratio of A- to HA = 10^(pH-pKA)[/B]

The Attempt at a Solution



- pH = pKa + log A/HA
- Ratio A/HA = 10^(pH-pKA) = 10^(4.99-4.76) = 1.70
- Mols of acid = 0.725 mL * 0.55 M = 0.3988 mM
- HA = (0.3988 - 1.30 * V) / (0.725 + V)
- A- = (1.30 * V) / (0.725 + V)
- A-/HA = (1.30 * V) / (0.725 + V) = 0.3988 = (1.30 * V) / (0.725 + V)

It has been a while since I've had general chemistry, and now I'm taking biochemistry and need to review acids, buffers, pH, pKa, molarity and volumes. I get to the last step and from here I completely forget what to do. Any help/hints would be appreciated.
 
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  • #2
Meadow_Lark said:
pH = pKa + log A/HA

OK

Ratio A/HA = 10^(pH-pKA) = 10^(4.99-4.76) = 1.70

OK

Mols of acid = 0.725 mL * 0.55 M = 0.3988 mM

Yes and no - watch your units.

HA = (0.3988 - 1.30 * V) / (0.725 + V)

OK

A- = (1.30 * V) / (0.725 + V)

OK

A-/HA = (1.30 * V) / (0.725 + V) = 0.3988 = (1.30 * V) / (0.725 + V)

No. But the mistake has nothing to do with the chemistry, just check your algebra. You started right with the A-/HA ratio, but instead of plugging correct formulas/numbers (which you correctly calculated earlier) you did something strange. Plug them as it should be done and solve for V, that's all.
 

1. What is the Henderson Hasselbalch equation and how is it used?

The Henderson Hasselbalch equation is a mathematical formula used to calculate the pH of a buffer solution. It is written as pH = pKa + log([A-]/[HA]), where pKa is the acid dissociation constant, [A-] is the concentration of the conjugate base, and [HA] is the concentration of the weak acid in the buffer solution. This equation is used to determine the pH of a buffer solution and to make adjustments to the buffer components in order to maintain a desired pH level.

2. How do buffers maintain a stable pH?

Buffers maintain a stable pH by resisting changes in pH when small amounts of acid or base are added. This is possible because buffers are composed of a weak acid and its conjugate base, which can neutralize any added acid or base. The Henderson Hasselbalch equation is used to calculate the ratio of acid to base in the buffer solution, ensuring that the pH remains relatively constant.

3. What factors affect the buffering capacity of a solution?

The buffering capacity of a solution is affected by the concentrations of the weak acid and its conjugate base, as well as the overall volume of the solution. Higher concentrations of the buffer components and larger solution volumes result in a higher buffering capacity. Temperature can also affect the buffering capacity, as changes in temperature can alter the dissociation of the weak acid.

4. How are Henderson Hasselbalch buffers prepared?

Henderson Hasselbalch buffers can be prepared by mixing a weak acid with its conjugate base in a specific ratio. The concentrations of the buffer components can be adjusted to achieve the desired pH using the Henderson Hasselbalch equation. It is important to note that the final volume of the solution must be taken into account when calculating the concentrations in order to maintain the correct ratio.

5. What are some common applications of Henderson Hasselbalch buffers?

Henderson Hasselbalch buffers are commonly used in laboratory experiments and in medical settings. In the laboratory, they are used to maintain a specific pH for reactions that are sensitive to changes in acidity. In medicine, these buffers are used to maintain a stable pH in bodily fluids such as blood and urine, as well as in medications that need to be administered at a specific pH.

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