# Creating a pH 6.7 Buffer Solution with Imidazole and C3H5N2Cl

• ElectronicError
In summary, the problem asks for a aqueous buffer solution of pH=6.7 with a capacity to absorb 20 mL of either 0.02 M HCl or 0.02 M NaOH without a pH change of more than +/- 0.1. Using the Henderson-Hasselbach equation and the given Ka for C3H4N2, a buffer concentration of 1.02 x 10^-3 was calculated. By using 40.6 mL of C3H4N2 and adding either HCl or NaOH dropwise until the desired pH is reached, a buffer solution with the desired properties can be created.
ElectronicError
I have worked through the problem and spent quite a bit of time on it but am not extremely confident in my solution. I would just like someone to check my work. Cheers.

## Homework Statement

-Need 0.4 L of an aqueous buffer solution of pH=6.7
-Have access to 0.02 M HCl, 0.02 M NaOH, 0.01 M C3H4N2, and 0.01 M C3H5N2Cl
-Will use Imidazole (C3H4N2) as weak base. Will use C3H5N2Cl as conjugate acid.
-Given Kb for C3H4N2 = 9.0 x 10^-8
-The buffer must have the capacity to absorb 20 mL of either 0.02 M HCl or 0.02 M NaOH and undergo a pH change of no more than +/- 0.1.

## Homework Equations

Henderson-Hasselbach

## The Attempt at a Solution

(Ka)(Kb) = Kw = 1 x 10-14
Ka * 9.0*10^-8 = 1 * 10^-14
Ka = 1.1 x 10^-7

-log(1.1 x 10^-7) = pKa ~ pH = 6.95

pH = pKa + log([base]/[acid])

6.7 = 6.95 + log([base]/[acid])

[base] / [acid] = 10^-0.25 = 0.56 (reasonably close to 1)

Use 1.56 x 10^-5 M for [base] and 0.001 M for [acid]

Buffer concentration = 1.02 x 10^-3

#mol weak base = (buffer concentration) * (desired final volume) = (1.02 x 10^-3) * 0.4 L = 4.06 x 10^-4 mol

0.01 M = 4.06 x 10^-4 mol / ? L

4.06 x 10^-2 L = 40.6 mL C3H4N2

In a 400 mL beaker, add distilled water to 40.6 mL C3H4N2 until most of the desired final volume is reached. Add HCl or NaOH dropwise until the pH reaches 6.7. Add distilled water to the 400 mL line.

Ummm..

:zzz:

This is my last, desperate call for help. Surely someone can lend a hand?

ElectronicError,

I have been trying to think about this one for you. Do you need to use all of those given solutions, or are you permitted to just use 2 or 3 of them?

My first attempt would be to begin with the imidazole hydrochloride and use it as an acid; find the amount of NaOH base titrant necessary to reach a pH of 6.7. Now, instead of performing that partial neutralization, think of the number of moles of imidazole which would be equivalent; and use correspondingly less amount of moles of the imidazole hydrochloride.

... I know that was not complete, but it might be a start. Take care in case I misjudged anything in that method.

## 1. What is a buffer solution?

A buffer solution is a solution that resists changes in pH when small amounts of acid or base are added. It consists of a weak acid and its conjugate base, or a weak base and its conjugate acid.

## 2. Why are buffer solutions important?

Buffer solutions are important because they help maintain a stable pH, which is crucial for many biochemical and chemical reactions. They also prevent sudden changes in pH that could be harmful to living organisms or alter the results of experiments.

## 3. How do you make a buffer solution?

A buffer solution can be made by mixing a weak acid or base with its conjugate salt. The ratio of the acid or base to its conjugate salt determines the pH of the buffer solution. Alternatively, a buffer solution can also be made by partially neutralizing a strong acid or base with a weak acid or base.

## 4. What is the Henderson-Hasselbalch equation?

The Henderson-Hasselbalch equation is a formula used to calculate the pH of a buffer solution. It is pH = pKa + log [conjugate base]/[weak acid], where pKa is the acid dissociation constant and [conjugate base] and [weak acid] represent the concentrations of the buffer components.

## 5. How do you choose the appropriate buffer solution?

The appropriate buffer solution can be chosen based on the desired pH range and the pKa of the weak acid or base. It is important to choose a buffer with a pKa close to the desired pH for optimal buffering capacity. Additionally, the components of the buffer should be compatible with the experiment or application it will be used for.

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