Purpose
In the course of our instruction here at MHS we often end up with waste material that cannot just be flushed down the drain.  Often this waste will sit around for months until I have time to "clean it up" for disposal.  Since we pay by the pound to dispose of our nasties, it is best to get the water out if we can.  It is also a good idea to be sure the solid waste left behind is neutral (a "salt") instead of acidic or basic.  In this lab you will neutralize a solution of unknown acidity, filter out the solids, and dispose of the products properly.

Procedure
As much metal as possible should be precipitated out.  This may be accomplished by the addition of a sulfide compound (Na2S is most common) or often a hydroxide (NaOH, KOH, LiOH).  The solid should be filtered out before the acid is neutralized, as pH may affect solubility.

1. Obtain a sample of the waste, and record it's volume.
2. Determine the pH of your sample using a pH meter.  Use the pH to calculate the hydrogen concentration from the formula pH = -log[H+].
3. Determine the approximate amount of base to add.  You may wish to add the base drop-wise as a solution, or as a solid.  You may add LiOH, NaOH, or KOH.
4. Clean and neutralize your sample.  The solid goes in the metallic waste receptacle, the clean neutral water can be flushed down the drain.
5. Now get a much larger sample, and repeat the procedure you just carried out, but "scaled up."

[MHS AP Chem page]