Weak acid/strong base titration (Acetic acid/NaOH)

In summary: If so then 25mL of that would be diluted to 250mL of water. If not, then you would need to convert the moles of acetic acid to grams.
  • #1
MadmanMurray
76
0
I did an acid/base titration with acetic acid and sodium hydroxide to determine the concentration of acetic acid present in vinegar but I'm not quite sure how to go about calculating the concentration of it.

First things first we dissolved 25ml of vinegar into 250ml of water and filled the burette to its 0 mark with this solution. We then added 25ml of 0.1M NaOH solution to an Erlenmeyer flask and added a few drops of phenolphtalein indicator. Then we titrated and watched as the liquid in the flask went from bright pink to completely clear then recorded the volume in the burette.

I this formula M2V2/b = M1V1/a for calculating concentration but I'm wondering if I have to calculate the amount of H+ ions from the acetic acid and OH- ions from the NaOH present in the solutions before I can go ahead. I'm not quite sure how this works for a weak acid is there a general rule like "1 dissociated H+ ion for every 2 moles of weak acid while the ratio is 1:1 for a strong acid?"

One other quick question on the side. I have 25ml of 0.1M NaOH solution so to calculate the moles present I just type 25/1000 x 0.1 into my calculator but this gives me a ridiculously low number which I doubt the teacher would expect us to deal with. Am I doing something wrong here?
 
Last edited:
Physics news on Phys.org
  • #2
The calculation is simpler than that.
Chemists say in their loose fashion :smile: you have neutralised the acetic acid.

But if you want to be confident you will have to know what a pH against added base curve looks like (so you have to know what pH is), what pK is, and the fact that the pK of phenolphtalein is around 9.
 
  • #3
MadmanMurray said:
One other quick question on the side. I have 25ml of 0.1M NaOH solution so to calculate the moles present I just type 25/1000 x 0.1 into my calculator but this gives me a ridiculously low number which I doubt the teacher would expect us to deal with. Am I doing something wrong here?

No, that's the correct amount. And it is not ridiculously low, it is just 0.25 mmol :wink:
 
  • #4
Thanks. I just did the calculation and my results seem reasonable. The average amount of diluted vinegar it took to neutralize the 25ml 0.1M NaOH solution was 29ml.

My results were
Concentration of diluted vinegar = 0.09M
Concentration of undiluted vinegar = 0.35M

I'm confused about how to get the percentage of acetic acid in the vinegar if there are 0.35 moles of acetic acid per liter of vinegar. 0.35M is 21 grams but I don't know how to convert mass to volume.
 
Last edited:
  • #5
At first you stated 25 mL were diluted to 250 mL. So the general approach is OK, but whether the number is OK - I don't know.

Watch significant numbers. Were you given 0.1M NaOH, or 0.1000M (or something like that)?
 

1. What is a weak acid/strong base titration?

A weak acid/strong base titration is a chemical process in which a strong base, such as sodium hydroxide (NaOH), is gradually added to a solution containing a weak acid, such as acetic acid (CH3COOH), until the solution reaches neutral pH. This process is used to determine the concentration of the weak acid in the solution.

2. Why is acetic acid commonly used as the weak acid in this titration?

Acetic acid is a common weak acid that is easily obtainable and has a known concentration. It also has a relatively low molecular weight, making it easier to dissolve in water. Additionally, acetic acid has a pH close to neutral, making it suitable for titration with a strong base like NaOH.

3. How is the endpoint of the titration determined?

The endpoint of the titration is determined using an indicator, which is a substance that changes color when the solution reaches a specific pH. In the case of weak acid/strong base titration, a commonly used indicator is phenolphthalein, which turns pink at a pH of 8.2.

4. What information can be obtained from this titration?

This titration can provide information about the concentration of the weak acid in the solution. By measuring the volume of the strong base required to reach the endpoint and using the known concentration of the base, the concentration of the weak acid can be calculated using the equation: Concentration of weak acid = (Volume of strong base x Concentration of strong base) / Volume of weak acid.

5. What are some sources of error in this titration?

Some sources of error in this titration include inaccurate measurements of volumes, human error in identifying the endpoint, and impurities in the chemicals used. To minimize these errors, it is important to use precise measuring equipment, repeat the titration multiple times, and ensure the purity of the chemicals being used.

Similar threads

  • Biology and Chemistry Homework Help
Replies
3
Views
1K
  • Biology and Chemistry Homework Help
Replies
2
Views
2K
  • Biology and Chemistry Homework Help
Replies
3
Views
1K
  • Biology and Chemistry Homework Help
Replies
1
Views
1K
  • Biology and Chemistry Homework Help
Replies
1
Views
1K
  • Biology and Chemistry Homework Help
Replies
7
Views
4K
  • Biology and Chemistry Homework Help
Replies
2
Views
2K
  • Biology and Chemistry Homework Help
Replies
23
Views
2K
  • Biology and Chemistry Homework Help
Replies
16
Views
3K
  • Biology and Chemistry Homework Help
Replies
1
Views
1K
Back
Top