MHS AP Chemistry
Identification of an Unknown Polyprotic Acid
In this experiment, you will be applying concepts learned in chapters
15-17 (and earlier, I guess) to identify an unknown polyprotic acid by
determining the Ka values and the molar mass.
-
Measure between 0.100 and 0.200 g of the unknown polyprotic acid.
mass of weighing dish |
__________ |
___ |
mass of weighing dish + acid |
__________ |
___ |
mass of acid |
__________ |
___ |
-
Dissolve the acid in about 50 mL of distilled water.
-
Titrate with 0.1 N NaOH solution.
-
Graph the titration curve, and determine the values of Ka for the acid.
Clearly indicate the lines you are using on your graph. If a value
is not present, leave it blank.
|
pH (=pKa) |
Ka |
first equivalence ½ way point |
__________ |
__________ |
second equivalence ½ way point |
__________ |
__________ |
third equivalence ½ way point |
__________ |
__________ |
-
Determine the number of moles of base required to reach the first equivalence
point.
-
How many equivalents of acid were neutralized as of the first equivalence
point? Remember what an "Equivalent of Acid" is!
-
Use your results so far to calculate the molar mass of the acid.
-
Use the table on page 1016 of your textbook to identify the polyprotic
acid. Compare the accepted values for the acid you choose with the
experimental values you determined today. If there is more than one
possibility, show them.
[MHS AP chem page]