Using drying agents

Some salts readily incorporate water into their crystal lattice.  Thus if the salt starts out without any water (the anhydrous form of the salt), it may grab water from its surroundings- effectively drying the surroundings.

This should not be new to you since you did a CHEM1211 experiment with this concept.  You heated a hydrated salt with a flame and calculated the amount of hydration.  As a demonstration before this experiment, Ms. Nguyen heated a hydrated salt and there were visible differences- a copper salt turned from blue (hydrated) to greenish (anhydrous) or perhaps you saw a cobalt salt turn from red (hydrated) to purple/blue (anhydrous).

In order to dry and organic sample, you must also carefully observe the changes as the salt goes from anhydrous to hydrated.  You will most likely be using anhydrous sodium sulfate (Na₂SO₄) as a drying agent.

When anhydrous, sodium sulfate is a loose, granular solid. video (5 sec)

The hydrated form is clumped together and is NOT loose. video (5 sec)

To dry your sample

1.  Check to make sure you can't see any water layer or water droplets.  If there is enough there to see then it will require so much sodium sulfate that you will probably lose a tremendous percent of your yield.  Visible droplets are best removed with a pipette.

2. Add a small scoopful of anhydrous sodium sulfate and swirl the flask  The sodium sulfate will take any available water from the liquid, and as a result of becoming hydrated, the sodium sulfate will clump together.  One the three situations below will occur:

• If the sample was already dry, the sodium sulfate will remain loose and granular.  Give it several minutes to make sure.  You are done with adding sodium sulfate.
• If there was just a little bit of water, and you added enough sodium sulfate to remove all of it, you will see some of the sodium sulfate clumped (it removed the water), while the rest of the sodium sulfate is loose and granular (there is no water for it).  Give it several minutes to make sure.  You are done with adding sodium sulfate.
• If there was more water than the sodium sulfate could handle, then all of the sodium sulfate will clump and none of it will be loose and granular.  YOU ARE NOT DONE.  You need to add another scoopful of sodium sulfate.  Eventually you will have some of the sodium sulfate remain loose and granular.  Only at that point will you be done adding sodium sulfate.

Bottom line:  your sample is not dry until you have sodium sulfate present that does not clump.

3.  Keep the top of the sodium sulfate bottle closed!!!!!!!!  The sodium sulfate will remove humidity from the air to become hydrated (and therefore useless to you).

4.  To remove your sample from the drying agent, pour off the liquid while leaving the solid behind (a process called decanting).

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