Deduce the Identity of Unknown Compounds

In this portion of the lab you will have four unknowns to identify. Two will be one of the compounds you've already worked with, one will contain an anion you've worked with, and another a cation you've worked with in this lab.

• The latter two are more difficult to determine because the observations won't match perfectly with the observations for any one compound. Rather, they will match with the observations for the reactions that involved that anion or cation as the reactive species. Think back to the spectator ions discussed in the introduction. They are not reactive species. For example, in the reaction between potassium iodide and lead(II) nitrate, it's the iodide anion and the lead cation that create the products you observe. If your unknown were Pb²⁺, you would expect the same results (formation of a yellow precipitate) from a reaction with potassium iodide. However, if your unknown was nitrate, you would not.
• You'll have to think carefully about what happens during reactions, but try not to get overwhelmed. You have several ways to determine your unknowns. Really, your experimental procedure is up to you! The following are suggestions. Just be sure to write down your methods and your observations.

Set up another reaction chart. This time use the unknowns chart. It has a lot of room for you to experiment.

click here for full-size .pdf

You will also want to label the wells you keep your unknown microburettes in, as well as the microburettes themselves.

Observe the color of your unknowns.

Test each unknown with the Universal Indicator.

Mix each unknown with your known compounds.

Binary mix your unknowns with each other.

You may want to redo some of the known reactions for comparison.

When you think you know the identity of your compounds, show your results to your TA.

Back

Next