Calculating H3O+ Concentration Using Buffer Solution

In summary, the conversation discusses the calculation of the H3O+ concentration in a solution containing 5.3e-2M HCl and 7.70e-2 M NaC2H3O2. The solution involves using the Kb and Ka values, as well as ICE tables and the Henderson-Hasselbalch equation to find the correct concentration. The previous question involved a similar scenario but with different values, leading to a different result.
  • #1
Hockeystar
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Homework Statement



What is the H3O+ concentration with the following scenario

5.3e-2M HCl and 7.70e-2 M NaC2H3O2

Homework Equations



Kw = Kb(Ka) ICE tables

The Attempt at a Solution



Both solutions 100% dissociation

The HCl should be fully neutralized giving 7.70e-2 - 5.3e-2 = 0.024M of the acetate left. Knowing the Kb of acetic acid is 5.56e-10 I set up an ICE table (5.56e-10*0.024)1/2 to find [OH-] to be 0.0000037. Convert that to what H+ concentration by taking 1e-14/0.0000037 = 3e-9. This answer is wrong. Could somebody point out where I went wrong.
 
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  • #3
The problem is I used the HH equation in my last question and failed. Should I just use the HH equation with the acetic ion concentration being the concentration of HCl and the acetate ion concentration is just the original concentration subtract HCl concentration?
 
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  • #4
That's the correct approach here.

What was the previous question? I guess there was a reason why HH was not applicable.

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  • #5
Thanks for your help just solved this question.

The previous question was 0.1 M NaNO2 and 0.05 HNO2. The Ka was 4e-4. I kept on getting 3.70 to be the pH which meant [H+] was 0.0002 but the answer was 3.6e-4.

EDIT. Masteringchemistry wanted we to assume their Ka value in their textbook which was twice as big of a value everywhere else on the internet grrrrrrrrrrrrrrrrrrrrrrr.
 
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1. What is a chemistry buffer?

A chemistry buffer is a solution that is able to resist changes in pH when an acid or base is added to it. It is composed of a weak acid and its conjugate base, or a weak base and its conjugate acid.

2. Why are chemistry buffers important?

Chemistry buffers are important because they help maintain a stable pH in a solution, which is crucial for many chemical reactions to occur. They are also commonly used in biological systems to regulate pH levels.

3. How do I choose the right chemistry buffer?

The right chemistry buffer is chosen based on the desired pH range and the pKa value of the weak acid or base used. The pKa value should be within one unit of the desired pH for the buffer to be effective.

4. Can a buffer be made from any weak acid or base?

No, not all weak acids or bases can be used to make a buffer. The pKa value must be within a certain range and the acid or base must be able to form a conjugate pair with its corresponding salt.

5. How do I prepare a chemistry buffer?

To prepare a chemistry buffer, you will need to mix a weak acid or base with its conjugate salt in the desired ratio. The solution should then be adjusted to the desired pH by adding small amounts of acid or base if needed.

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