Deduce the Identity of Unknown Compounds
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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.
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Set up another reaction chart. This time use the unknowns chart.
It has a lot of room for you to experiment.
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click here for full-size
.pdf
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You will also want to label the wells you keep your unknown
microburettes in, as well as the microburettes themselves.
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Observe the color of your unknowns.
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Test each unknown with the Universal Indicator.
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Mix each unknown with your known compounds.
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Binary mix your unknowns with each other.
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You may want to redo some of the known reactions for comparison.
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When you think you know the identity of your compounds, show your
results to your TA.
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