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

2. 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	_______	_______	_______	_______

3. How can you recognize a saturated solution in a test tube?
4. Make one test-tube-full of a saturated solution of the unknown provided. Write your name on it with a pencil or a sharpie.
5. 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? ]
6. 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? ]
7. Put all your data into a clearly constructed table, so you can understand it tomorrow. Include which unknown you had.
8. 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!
9. Using your calculated solubility, which known material from the table in #2 is your unknown material?
10. Calculate the % error of your measured solubility from the one you looked up. Refer to previous notes for the percent error formula.

OK, NOW WHAT?

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?

• PS-1.1.a Students demonstrate an understanding of the structure of matter by utilizing appropriate data (related to chemical and physical properties), to distinguish one substance from another or identify an unknown substance.
• PS-1.4.b Students demonstrate an understanding of the structure of matter by writing formulae for compounds and developing basic (excluding transition elements) models using electron structure.
• PS-1.3.b Students demonstrate an understanding of the structure of matter by predicting the relative physical and chemical properties of an element based on its location within the periodic table.
• PS-1.3.a Students demonstrate an understanding of the structure of matter by identifying and explaining the basis for the arrangement of elements within the periodic table (e.g. trends, valence electrons, reactivity, electronegativity, ionization)
  

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