Experiment 6
| The Identification of Unknown Substances |  |
Procedure and Results
Stockroom
 | Pick up your unknowns. |
Procedure
One Component Unknown Use any of the tests described in the Background section to eliminate compounds as possible components from your unknown. Solubility and the effect of acid are especially helpful tests to start with because they can eliminate the largest number of possible candidates. It is useful to compare the properties with those listed in the Table. Once you have reduced your list of candidates to a manageable number, all of your tests should be done both on your unknown and on authentic samples. Record the results that you find for both your unknown and the authentic samples. Carry out the tests until only one compound remains as a possibility and its properties agree with the properties that you obtain for an authentic sample of that compound.
Two Component Unknown Because this unknown contains two compounds that differ greatly in their solubility in water, the first step in your analysis is to use this to separate the two compounds. Take approximately one-third of your unknown sample and put it into a small test tube. Add water and mix thoroughly using a stirring rod. Centrifuge this mixture and remove and save the clear solution. This is the soluble component of your unknown. Wash the remaining solid by adding water and again mix thoroughly and centrifuge. Remove the clear liquid and discard it. Repeat this washing step one more time. The remaining solid should be a pure sample of the insoluble component of your unknown.
Analyze each of the samples (soluble and insoluble) as you did for the One Component Unknown.
Both of the samples contain compounds chosen from the Table below.
Candidates for Unknowns
| NAME | FORMULA | MELTING POINT(ºC) | SOLUBILITY (g/100mL) |
| ammonium bicarbonate | (NH4)HCO3 | 107.5 | 12 |
| ammonium carbonate | (NH4)2CO3 | d58 | 100 |
| ammonium sulfate | (NH4)2SO4 | d280 | 76 |
| calcium carbonate | CaCO3 | d825 | 0.0015 |
| calcium chloride | CaCl2 | 772 | 60 |
| calcium hydroxide | Ca(OH)2•H2O | 580 | 0.185 |
| calcium sulfate | CaSO4•1/2H2O | -1/2H2O, 163 | 0.3 |
| dextrose | C6H12O6 | 146 | very soluble |
| magnesium carbonate | MgCO3 | d350 | 0.01 |
| magnesium chloride | MgCl2 | 708 | 54 |
| magnesium sulfate | MgSO4•7H2O | -6H2O, 150 | 71 |
| potassium bicarbonate | KHCO3 | d100 | 22 |
| potassium carbonate | K2CO3 | 891 | 112 |
| potassium chloride | KCl | 776 | 35 |
| potassium sulfate | K2SO4 | 588 | 7 |
| sodium bicarbonate | NaHCO3 | -CO2, 270 | 7 |
| sodium carbonate | Na2CO3•H2O | -H2O, 32 | 17 |
| sodium chloride | NaCl | 801 | 209 |
| sodium sulfate | Na2SO4 | 884 | 5 |
| sand | SiO2 | --- | i |
| sucrose | C12H22O11 | 186 | 180 |
Results
Record the results for each of the tests on your unknown samples along with the results for the authentic compounds when tests on these were also done. You will need the record of these results to help to eliminate the unlikely compounds and to refer to in the Conclusion section of your write-up of this experiment.
02.03.04