# with "Triprotic Acid Titration" Question

• pandamonium786
In summary, the unknown triprotic acid H3X has a molar mass of 31.9g/mol, a first ionization constant of 1.94x10-5 M-1, and a second ionization constant of 5.78x10-5 M-1.
pandamonium786
Hey guys! So I have this chemistry problem which I'm finding very difficult.

QUESTION:
You have an unknown triprotic acid, H3X, and have titrated it with 22.53mL of NaOH. The pH of the unknown solution is 2.04 and the concentration is 48.028g/2L. While the concentration of the NaOH is 0.251mol/L. What is the molar mass, as well as the first and second ionization constant (Ka1) for the unknown triprotic acid H3X?

WORK SO FAR:
H3X + 3NaOH --------> Na3X + 3H2O
I know that if I solve for the concentration of the unknown by using the formula 3CaVa=CbVb I get 0.334 mol/L , but then what was the point of being given a concentration?

I really don't understand how to move forward from this point. So any help would be appreciated.

Hint: both concentrations are in different units. How can you convert between them?

Borek said:
Hint: both concentrations are in different units. How can you convert between them?

So could I do this then:

H3X + 3NaOH --------> Na3X + 3H2O

NaOH = 3[H3X] = 3(0.251mol/L) = 0.753mol/L

H3X=48.028g/2L=24.014g/L

Therefore, 0.753mol/L = 24.014g/L
Molar Mass = 24.014/0.753
= 31.9g/mol

You have titrated what volume of the acid? Not stated.
The volume of NaOH is not mentioned in your calculation. So the calculation is about no experiment.

It is basically quite simple. You can calculate the number of moles of NaOH used in the titration, from its molarity and volume used. This equals the number of moles of protons removed from the acid in the titration. That is probably a 3× 'the number of moles of the tribasic acid originally present that you titrated. (It might be a twice but you give no details of what you mean by 'a titration'.)

You give no information that enables us to say anything about pKa2. Once you know the molarity of the acid, from the pH 2.04 you can give a reasonable figure for pKa1.

If this was a real experiment anyone would need to know more about what it was than you have stated to say anything more.

For the diprotic acid full titration, the steps are outlined in this pdf: http://www.chem.purdue.edu/courses/chm321/lectures/lecture%2018%20(10-10).pdf
when it says: "The pH of the unknown solution is 2.04 and the concentration is 48.028g/2L." do you mean that the initial volume of H3X was 2L, and there were 48.028 g dissolved in the initial solution that was then titrated?
It says: "You have an unknown triprotic acid, H3X, and have titrated it with 22.53mL of NaOH." I think it means that this was the end-point of the 3 de-protonations, therefore:
mols of H3X = 1/3 * mol NaOH = 1/3 * [NaOH] * Vol NaOH
Also mols H3X = mass H3X / FW
So you can figure out the FW.
For the rest refer to the henderson-Hasselbalch equation as it pertains to the intermediate titration steps.
in the beginning (see step 1 in the pdf above)
[H+] ~= sqrt(Ka1*[H3X])
so you can calculate Ka1.
Then, at the first equivalence point you would have exhausted all the H3X and you are left with H2X- that is starting to deprotonate. Follow the formulas to figure out Ka2, etc.

## What is Triprotic Acid Titration?

Triprotic acid titration is a laboratory technique used to determine the concentration of a triprotic acid solution. It involves gradually adding a standardized base solution to an acid solution until the solution reaches a neutral pH, at which point the volume of base added is used to calculate the acid concentration.

## What is a triprotic acid?

A triprotic acid is a type of acid that contains three ionizable hydrogen atoms per molecule. These hydrogen atoms can be released as protons, making the acid capable of donating three protons in an acid-base reaction. Examples of triprotic acids include phosphoric acid and citric acid.

## What is the purpose of triprotic acid titration?

The purpose of triprotic acid titration is to determine the concentration of a triprotic acid solution. This information can be useful in various scientific and industrial applications, such as in the production of pharmaceuticals or in studying the properties of acids in solution.

## What equipment is needed for triprotic acid titration?

The equipment needed for triprotic acid titration includes a burette, a standardized base solution, an acid solution, an indicator (such as phenolphthalein or methyl orange), and a flask or beaker for mixing the solutions. A pH meter may also be used for more accurate measurements.

## What are some factors that can affect the accuracy of triprotic acid titration?

Some factors that can affect the accuracy of triprotic acid titration include incorrect measurement of solutions, improper mixing of solutions, and the presence of impurities or contaminants in the solutions. It is important to carefully follow the titration procedure and properly calibrate and maintain equipment to ensure accurate results.

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