Question

A solution of a theoretical triprotic acid was prepared by dissolving 4.037 g of solid in enough DI water to make 500.0 mL of solution.   10.11 mL of a 0.592 M solution was required to titrate 20.00 mL of this acid's solution.

Part A

What is the concentration of the acid solution?

Part B

What is the molar mass of the acid?

Hint: You need to calculate the total moles in the 500.0 mL solution (the full 500.0 mL was NOT titrated).

2-

How is the experiment "Molar Mass of a Known Acid" relevant to the "Molar Mass of an Unknown Acid"? More specifically, how do they complement each other?

Note: more than one of the following responses is true, but only one addresses this question.

Both experiments will involve using the data collected in a titration experiment to calculate the molar mass of an acid.

The data we collect in the "Known Acid" experiment will enable us to compare the molar mass of the known acid to the acid studied in the "Unknown Acid" experiment.

Both experiments make use of primary and secondary standards.

The former experiment will make use of the same glassware that will be used in the latter.

The results of the former experiment will be used to evaluate the accuracy of the titration technique that will be used in the latter experiment.

3- The procedure you will follow in this experiment will be very similar to the one you followed in the "Molar Mass of a Known Acid" experiment, but will differ in one significant respect. What is it?

The procedure you will follow in this experiment will be very similar to the one you followed in the "Molar Mass of a Known Acid" experiment, but will differ in one significant respect. What is it?

We will perform the analysis on an acid we do not know the identity of, instead of one we do know the identity of.

Since the procedure will be performed on both a known and an unknown acid, we will have to standardize two different sodium hydroxide solutions in this week's lab period.

The sodium hydroxide solution will already have been standardized, so we won't have to complete this part(s) of the procedure (make an oxalic acid solution and perform the required titrations).

The unknown will be provided to us as a premade solution.

We will perform Part C twice in the "Unknown Acid" experiment: once with a known acid, and once with a unknown acid.

4- You were able to calculate the true molar mass of the known acid in the "Molar Mass of a Known Acid" experiment because you knew the stoichiometry of the reaction between the known acid and the sodium hydroxide. However, since the acid you will work with in this experiment is unknown, you will not know the ratio in which it reacts with NaOH. How will you get around this problem?

You were able to calculate the true molar mass of the known acid in the "Molar Mass of a Known Acid" experiment because you knew the stoichiometry of the reaction between the known acid and the sodium hydroxide. However, since the acid you will work with in this experiment is unknown, you will not know the ratio in which it reacts with NaOH. How will you get around this problem?

By performing the molar mass calculation three times: once assumin the acid is monoprotic, once assuming it is diprotic, and once assuming it is triprotic.

By assuming the stoichiometry of the reaction between the unknown acid and sodium hydroxide is the same as that between the known acid and sodium hydroxide.

By calculating the acid's equivalent molar mass instead of its true molar mass.

By referring to the notation on the unknown acid's bottle, which will say wheter the acid is monoprotic, diprotic or triprotic.

By assuming the stoichiometry of the reaction between the unknown acid and sodium hydroxide is the same as that between the primary standard (oxalic acid) and sodium hydroxide.

5- Define the term "equivalence point".

Define the term "equivalence point".

The point in a titration at which the number of moles of added titrant equals the number of moles of compound in the flask being titrated.

The point in a titration of a diprotic acid in which half as many moles of NaOH as there are moles of acid present have been added to the flask. This quantity of NaOH is "equivalent" to what would be required to titrate a monoprotic acid.

The point in a titration at which the same number of moles of titrant used to titrate a known sample has been added to an unknown sample; they are the same or "equivalent" at this point.

The point in a titration in which stoichiometry amounts of each reactant have been added to each other.

An observable change in a titrated solution that indicates sufficient titrant has been added to drive the reaction to completion.

Answer 1

Titration

A) concentration of acid solution = 0.592 M x 10.11 ml/3 x 20 ml = 0.099752 M

B) molar mas of acid = 0.437 g/0.099753 M x 0.02 L = 219.043 g/mol

3. For the molar mass determination of unknown acid,

we will perform part C once with known acid and second with unknown acid.

4. If the stoichiometry of acid to base is not known,

By calculating acid equivalent molar mass instead of true molar mass.

5. Equivalent point,

The point in a titration at which the number of moles of added titrant equals the number of moles of compound in the flask being titrated.