Carnegie Mellon University

Suspicious Groceries: Procedure

  1. Data charts have been placed in plastic protector sheets. Put them on the bench top. The experiment will be done directly on the data sheets. Results should be recorded immediately on your result sheets. Wear safety glasses at all times.
  2. Using a straw scoop, place a pea-sized amount of corn starch on the blocks below the column marked CORN STARCH. Repeat with the other powders, except for the one marked “evidence". We will test that after all of the other tests have been completed. Be careful not to use a scoop in more than one sample, or to bump the data sheet and mix up the powders.
  3. Using a dropper, put 2-3 drops of vinegar onto the corn starch in the vinegar row. Carefully observe the powder-vinegar mixture and record what happens on your result sheet. Repeat with the other powders in the vinegar row. Use a stirring rod if necessary.
  4. Continue using iodine on the powders in the iodine row, and then with water in the water row. Record what happens after each test. Do not bump the data sheet and do not discard it yet!  A positive reaction to the iodine test indicates the presence of starch due to the formation of a colored starch-13 complex.
  5. At this point, we can use a strip of litmus paper to determine if the substances are acidic, basic, or neutral. Dip the end of a strip of litmus paper into the corn starch-water test solution on the data sheet. Record the color of the litmus paper on your results sheet. Repeat with all of the other water test solutions in the water row.
  6. Finally, look over your test results. Do you think that you could tell the powders apart on the basis of your results? Try it by analyzing the evidence by performing all of the tests. Record the results on your result sheet. Determine its possible identity.

See Suspicious Groceries relevant data sheets and charts [.pdf].


Discard used scoops and stirring rods.  Discard powder samples into a waste container and then wipe off test sheets.  Make sure all container lids are on securely.