Troubleshooting Buffer Solution Titration | Identifying Unknown Buffer in Lab"

  • Thread starter kooombaya
  • Start date
  • Tags
    Buffer
In summary, the conversation revolved around a lab experiment involving an unknown buffer solution and titration with NaOH and HCl to determine its pKa value. The pKa was found to be 4.52, but there was difficulty in identifying the buffer due to a Ka value of 3E-5 not matching any known values. The conversation also touched on the process of neutralizing the buffer and the wording used in the lab book. Ultimately, it was determined that the experiment involved shifting the pH of the buffer rather than achieving a neutral solution.
  • #1
kooombaya
36
0
This isn't really a homework problem. In lab we had an unknown buffer solution and we had to to titrate it with NaOH and HCl to try to identify what the buffer is. In the end I got my pka value equal to 4.52 I can't identify the buffer. My Ka is 3E-5 and I can't match any Ka values to this. Did I just totally screw up my lab??
 
Chemistry news on Phys.org
  • #2
Is there a list of buffers that you have to select from? Or can it be anything?
 
  • #3
Nope, we weren't given a list to choose from so I'm guessing it could be anything?
 
  • #4
Probably. Although some compounds are much more likely than others.

How did you get your pKa?
 
  • #5
I required 19.92 mL of NaOH to neutralize a 10 mL portion of my buffer. I did the same thing using another 10 mL portion of the buffer but this time with HCl and it took me 17 mL.

I then used the henderson-hasselbalch equation to find my pKa. I measured my pH of my buffer with a pH meter and got it to be 4.40.

I had already standardized my acid and base previously and got 0.1472 M NaOH and 0.1325 M HCl. Also I made sure to change the ml to L for the following calculations.

For the concentration of my base and acid I did this:


[A] = (19.92 ml NaOH x 0.1472 M NaOH)/10 mL = 0.293
= (17ml HCl x 0.1325 M HCl)/10 ml =0.225

4.40= pka + log [0.225]/[0.293]

pka= 4.52
 
  • #6
Posted something before thinking it was right... still wrong.
 
Last edited:
  • #7
kooombaya said:
I required 19.92 mL of NaOH to neutralize a 10 mL portion of my buffer. I did the same thing using another 10 mL portion of the buffer but this time with HCl and it took me 17 mL.

What do you mean by "neutralize the buffer"?
 
  • #8
Borek said:
What do you mean by "neutralize the buffer"?

This was how the question was stated in the lab book.
I found out what I did wrong by the way. Thanks for your time.
 
  • #9
kooombaya said:
This was how the question was stated in the lab book.

Can you explain what they meant? I have never seen something like that, even if it is wrong, I have nothing against knowing.
 
  • #10
Borek said:
Can you explain what they meant? I have never seen something like that, even if it is wrong, I have nothing against knowing.

From what I understood it goes something like this:
Say we added 10 mL of 0.1 M NaOH. Then this is the amount of acid in the buffer solution that reacted with the NaOH to reach a new equivalence point.
It's the same for HCl, except the HCl acts with the base in the buffer solution to reach a new equivalence point.
 
  • #11
So it was just shifting pH of the buffer by addition of strong acid or base. There was an acid base reaction involved (which can be technically called neutralization), but it didn't end with neutral solution.

Not the best wording if you ask me.

--
 
Last edited:
  • #12
Borek said:
So it was just shifting pH of the buffer by addition of strong acid or base. There was an acid base reaction involved (which can be technically called neutralization), but it didn't end with neutral solution.

Not the best wording if you ask me.
Yup exactly. Thanks again.
 

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 in a solution. This is crucial in biological and chemical processes, as many reactions are pH-dependent and can be disrupted by changes in pH. Buffer solutions also help prevent damage to cells and tissues.

3. How do I prepare a buffer solution?

To prepare a buffer solution, you will need a weak acid or base and its conjugate salt, along with water. The pH of the buffer solution can be adjusted by varying the ratio of the weak acid/base to its conjugate salt. It is important to use precise measurements and techniques to ensure the accuracy of the buffer solution.

4. Can I use any weak acid/base to make a buffer solution?

No, not all weak acids/bases can be used to make a buffer solution. The acid/base must have a pKa value close to the desired pH of the buffer solution in order to effectively resist pH changes. Commonly used weak acids for buffer solutions include acetic acid and citric acid, while commonly used weak bases include ammonia and diethylamine.

5. How do I know if my buffer solution is working?

You can test the effectiveness of your buffer solution by adding small amounts of acid or base and monitoring the pH. If the pH remains relatively constant, then the buffer solution is working. Additionally, using a pH indicator can help visualize the pH changes in the buffer solution.

Similar threads

Replies
4
Views
4K
  • Chemistry
Replies
9
Views
8K
Replies
2
Views
2K
Replies
2
Views
5K
Replies
4
Views
2K
  • Biology and Chemistry Homework Help
Replies
7
Views
5K
  • Chemistry
Replies
4
Views
4K
  • Chemistry
Replies
2
Views
3K
  • Introductory Physics Homework Help
Replies
1
Views
1K
Back
Top