How Do You Calculate the pH at Equivalence Points in Malonic Acid Titration?

I will try to work it out using the amphiprotic salt concept.In summary, malonic acid is a dibasic acid with pKa1 and pKa2 values of 2.85 and 5.70 respectively. The first and second equivalence points of a titration of 10cm^3 of 0.1 M malonic acid with 0.1 M sodium hydroxide have a pH of 7.77 and an unknown value, respectively. The pH at the first endpoint is incorrect and requires further calculation using the concept of an amphiprotic salt.
  • #1
nmr
7
0
Malonic acid can ionise in two stages as it is a dibasic acid.
The values of pKa1 and pKa2 of malonic acid are 2.85 and 5.70 respectively. Calculate the pH of the first and second equivalence points of the titration of 10cm^3 of malonic acid of concentration 0.1 M with sodium hydroxide of concentration 0.1 M.

my attempt at a solution:
maximum buffering capacity before first endpoint: pH=pKa1 = 2.85

[OH-] = [(Kw/Ka1)*(0.05)]^(0.5)
therefore pOH = 6.23
pH = 14-6.23 = 7.77

im stuck here as the answer given for the pH of the first endpoint is 3.50 and I have no idea how to work it out
 
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  • #2
First endpoint pH given as an answer is wrong, so don't worry if you can't reproduce it.

At first endpoint you have a solution of an amphiprotic salt.
 
  • #3
so is my pH value correct ?
 
  • #4
Nope.
 
  • #5
how would i go about solving for the pH then?
 
  • #6
I have pointed you in the right direction in my first answer.

If you plan to ignore hints please tell, so that I don't waste my time answering.
 
  • #7
ah ok sorry
 

1. What is dicarboxylic acid titration?

Dicarboxylic acid titration is a laboratory technique used to determine the concentration of a dicarboxylic acid in a solution. This involves adding a known amount of a base solution to the acid solution until the reaction reaches the equivalence point, at which the moles of acid and base are equal. By knowing the volume and concentration of the base solution, the concentration of the acid can be calculated.

2. How is dicarboxylic acid titration performed?

Dicarboxylic acid titration is typically performed using a burette, which allows for precise measurement of the base solution being added to the acid solution. The acid solution is placed in a flask or beaker, and the base solution is slowly added while stirring. An indicator is often used to signal when the equivalence point has been reached, such as phenolphthalein which turns the solution pink at a basic pH.

3. What are some common applications of dicarboxylic acid titration?

Dicarboxylic acid titration is commonly used in the pharmaceutical industry to determine the purity of drugs and active ingredients. It is also used in food and beverage production to measure the amount of acid in products like wine and fruit juices. Additionally, it is used in environmental testing to analyze the acidity of water samples.

4. What are some potential sources of error in dicarboxylic acid titration?

Some potential sources of error in dicarboxylic acid titration include inaccurate measurements of the base solution, incomplete mixing of the solutions, and the use of expired or contaminated chemicals. Human error, such as misreading the burette or flask markings, can also contribute to inaccuracies in the results.

5. How can the accuracy of dicarboxylic acid titration be improved?

To improve the accuracy of dicarboxylic acid titration, it is important to use high-quality and calibrated equipment, as well as fresh and properly stored chemicals. Taking multiple measurements and calculating the average can also help increase accuracy. Careful technique and attention to detail, such as ensuring complete mixing and accurate readings, can also improve the accuracy of the results.

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