OBJECTIVES/OVERVIEW

This experiment is very similar to the previous experiment.  However, you will work in a team of four to find the molar mass of a carboxylic acid in order to determine its identity.  This experiment will test your ability to work within a group to achieve a common goal.  I would recommend that the team of four split the responsibilities or you will not finish on time.

This lab can be split into two sections.  In the first section, you will prepare and standardize the NaOH solution like in the previous lab.  In this lab, you will use solid potassium hydrogen phthalate (KHP) instead of sulfuric acid.  KHP is a monoprotic carboxylic acid, which means that for every mole of KHP, one mole of NaOH will be required to neutralize it.

Once you determine the concentration of the NaOH solution very precisely, you can use this information to determine the number of moles of an unknown carboxylic acid.  If you have an accurate mass of the unknown carboxylic acid you used, you can determine its molar mass and identity.

Your unknown carboxylic acid will either be a monoprotic, diprotic, or triprotic carboxylic acid.  This means that you will need either one, two, or three moles of NaOH to neutralize each mole of your unknown carboxylic acid.  You need to take this into account on set-up 20.

This is an example of a monoprotic carboxylic acid.  For every mole of carboxylic acid, one mole of NaOH is needed to completely neutralize it.

 

This is an example of a diprotic carboxylic acid.  For every mole of carboxylic acid, two moles of NaOH are needed to completely neutralize it.

 

This is an example of a triprotic carboxylic acid.  For every mole of carboxylic acid, three moles of NaOH are needed to completely neutralize it.