Middletown High School
Chemsitry in the Community

Solubility of an Unknown Substance

The purpose of this activity is to remind ourselves of solution concepts while determining the identity of an unknown substance based on its solubility. Answer each of the questions below in your bound lab notebook.

  1. Know the definition of the following words:

    Solution Solute Solvent Decant
    Concentration Solubility Saturated Filtration
  1. Look up the following compounds in the CRC Handbook of Chemistry & Physics, or Lange's Handbook of Chemistry. Look for a table called "Physical Constants of Inorganic Compounds" or something similar (the title varies slightly depending on the edition). Fill in the table below. For solubility, use the one listed for "cold water."

    Name Formula Color Solubility Unit of Measure
    Cesium Chloride _______ _______ _______ _______
    Lithium Chloride _______ _______ _______ _______
    Potassium Bromide _______ _______ _______ _______
    Potassium Chloride _______ _______ _______ _______
    Rubidium Chloride _______ _______ _______ _______
    Sodium Bromide _______ _______ _______ _______
    Sodium Chloride _______ _______ _______ _______
    Sodium Iodide _______ _______ _______ _______
  1. How can you recognize a saturated solution in a test tube?
  2. Make one test-tube-full of a saturated solution of the unknown provided. Write your name on it with a pencil or a sharpie.
  3. Describe how you would obtain a test tube that contained only the saturated solution, without any extra material or impurities. Show what you just wrote to your teacher. If you get the OK, then do it.
    [ _____ OK? ]
  4. Describe how you would/can separate the solvent from the solute of your solution. Include steps required to determine the amount of each by the time you are finished. Show what you just wrote to your teacher. If you get the OK, then do it.
    [ _____ OK? ]
  5. Put all your data into a clearly constructed table, so you can understand it tomorrow. Include which unknown you had.
  6. Determine the mass of solute, mass of solvent, and solubility (in g/100 g of water) of your unknown. Make sure you understand your calculations. There may be a quiz later!
  7. Using your calculated solubility, which known material from the table in #2 is your unknown material?
  8. Calculate the % error of your measured solubility from the one you looked up. Refer to previous notes for the percent error formula.


In your notebook, you should have:

  1. Looked up a bunch of solubilities.
  2. Made a saturated solution of an unknown X, Y, or Z.
  3. Measured the mass of solute and of solvent that you used, and calculated its solubility.
  4. Identified your unknown based on solubility.
  5. Determined the % error of your measurement.

To pass in, each student should make a graph.

  1. The x-axis should be the atomic number of the anion attached to potassium, or sodium (if the anion was oxygen, that number would be 8). Start at zero.
  2. The y-axis should be solubility, in grams per 100 g water. Start at zero.
  3. Make one trend-line for sodium compounds, and another for potassium compounds.
  4. Use your graph to predict the solubility of sodium fluoride. Show this work on the graph.

Read those instructions twice. It's not that bad. But, as I mentioned, there may be a quiz on any part of this later. So make sure you know of what you write.

Wait a second, what about GSEs or Standards?

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