Question

1. Discuss what the following errors or changes in procedure will have on your titration and on the calculated molar mass of your acid

a.Reached the endpoint prior to all of the acid dissolving.

b.You stopped the titration and recorded the final buret volume when a deep

pink/red color was seen.

c.You used twice the amount of water to dissolve the acid.

**Correct answers will clearly state if the calculated molar mass is higher or lower than the correct value or if there is no effect.

2. What if the unknown acid was really a triprotic acid (three H+ ions to be donated) instead of a diprotic acid

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a. Write the formula for the triprotic acid and a balanced equation for the titration reaction.

b. Using your experimental data from trial #2 (assuming the acid mass is really that of the triprotic acid), calculate the molar mass of the triprotic acid.

c. Compare the calculated molar masses of the triprotic acid with the diprotic acid molar mass.

3. Consult the supplemental page on Canvas with a list of possible diprotic acids. Using molar masses, what is/are the most likely identity(ies) of the unknown acid?

Answer 1

1. Discuss what the following errors or changes in procedure will have on your titration and on the calculated molar mass of your acid

a.Reached the endpoint prior to all of the acid dissolving:

If the endpoint reaches before all of the acid is dissolved then we will have less volume of basic solution used in titration. This will result in less number of moles of base used. This further results in less calculated molar mass of unknown acid and which gives rise to lesser molarity of the unknown acid than the correct value.

b.You stopped the titration and recorded the final buret volume when a deep pink/red color was seen.

Deep pink/red color indicates more volume of basic solution used in titration. This will result in more number of moles of base used. This further results in higher calculated molar mass of unknown acid and which gives rise to higher molarity of the unknown acid than the correct value.

c.You used twice the amount of water to dissolve the acid.

This has no influence on the titration value of basic solution used. This it does not influence the calculated molar mass and molarity of the unknown acid.   

2. What if the unknown acid was really a triprotic acid (three H+ ions to be donated) instead of a diprotic acid

—

a. Write the formula for the triprotic acid and a balanced equation for the titration reaction.

H₃PO₄ + 3 NaOH ----------------------> Na₃PO₄ + 3 H₂O

b. Using your experimental data from trial #2 (assuming the acid mass is really that of the triprotic acid), calculate the molar mass of the triprotic acid.

experimental data from trial #2 NOT GIVEN.

c. Compare the calculated molar masses of the triprotic acid with the diprotic acid molar mass.

3. Consult the supplemental page on Canvas with a list of possible diprotic acids. Using molar masses, what is/are the most likely identity(ies) of the unknown acid?

Supplemental page NOT SHOWN.