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How to Test Compounds

Some chemists have the exciting task of finding out what a sample is. They run a myriad of tests, each one designed to confirm or eliminate the possibility of the sample's identity. The tests they perform are a mixture of manual bench top procedures, while others involve the use of high technology instrumentation. Each test result yields clues as to the identity of the compound. Early testing not only provides information but also helps to direct subsequent testing to narrow the identity. Comparison of the results of the testing with the information provided in the wealth of chemical literature occurs. The Handbook of Chemistry and Physics list the physical properties for a multitude of compounds.

Things You'll Need

Wire loop
Cork
Bunsen burner
Spatula
Litmus paper
Test tubes
Test tube racks
Solubility reagents

Instructions

General Tests
- 1
  Examine the compound visually. Record its color and the shape of the crystals if you can discern crystals in the sample.
- 2
  Twist a piece of nichrom wire into a small loop and thread the end opposite the loop through a cork to form a handle. Dip the loop into a small amount of your unknown compound and record the observations you make as the sample burns in the flame of a Bunsen burner. Many metal ions give off a characteristic color in the flame.
- 3
  Check the pH of the compound by adding a small amount of your compound to a test tube containing water. Use a small stirring rod to place a small drop on a piece of red and blue litmus paper. If the drop on a piece of blue litmus paper turns red, then the compound makes water acidic when it dissolves, but if the drop turns the red paper blue, then the compound makes the water basic when it dissolves.
Solubility Tests
- 4
  Examine the solubility of the compound by investigating how well the compound dissolves in various solvents.
- 5
  Place a row of test tubes in a test tube rack and place a small amount of solvent in each of the test tubes. Select solvents that will test some characteristic of the compound. Water, acids and bases will all examine the polarity of your compound. Solvents like alcohol and hexane will also investigate your compounds polarity, but will also look at the organic character of your compound.
- 6
  Add a spatula tip of your compound to each of the test tubes and record your observation of how the compound reacts with the solvent. Distinguish between the compound floating on the surface, sinking to the bottom of the tube, or dissolving in the solvent.
- 7
  Heat the tubes that contain compound that didn't dissolve. The heating process can change a compound's solubility.
- 8
  Evaluate all these pieces of information to discern which other tests you should perform.

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