Illustrated Guide to Home Chemistry Experiments

392 DIY Science: Illustrated Guide to Home Chemistry Experiments

POCEDURER
This lab has two parts: preparation of the reagents and running
the tests.

PI: RTA pREREpA REAGENTS
Before running the tests, we need to prepare the reagents. The
amount of each reagent you need depends on the number of
tests you plan to run and whether you run the tests on a spot
plate or in test tubes. We decided to prepare about 5 mL of each
reagent, which is sufficient for many tests using a spot plate. If
you are using test tubes, we recommend preparing at least 10 mL
of each reagent, depending on how many tests you plan to run.

1. If you have not already done so, put on your splash
   goggles, gloves, and protective clothing.


2. To prepare the Marquis reagent, add five drops (0.25 mL)
   of 40% formaldehyde to 5.0 mL of concentrated sulfuric
   acid. Stir thoroughly to mix, and store the Marquis
   reagent in a labeled Barnes bottle or other airtight
   container.


3. The nitric acid reagent is simply concentrated (~70%)
   nitric acid. For convenience, you may wish to transfer
   5.0 mL of concentrated nitric acid to a dropper bottle or
   whatever other container you’re using for reagents. Note
   that concentrated nitric acid may react with rubber or
   plastic stoppers, so a dropper bottle with a ground glass
   seal is the best choice.


4. To prepare the ferric chloride reagent, dissolve 0.10 g
   of anhydrous ferric chloride (or 0.17 g of ferric chloride
   hexahydrate) in 5.0 mL of water.

Use freshly prepared reagents to ensure that your results
are reproducible.

PII: RTA RHENU T TESTS

Although you can run several tests simultaneously if time is short,

it’s better to make a separate test run for each substance. We

suggest that you test each substance with each reagent both in

solid form and dissolved in the solvent recommended for that

reagent (chloroform for Marquis reagent and the nitric acid

reagent, and methanol for the ferric chloride reagent.) For each

substance you are testing, take the following steps:

1. If you have not already done so, put on your splash
   goggles, gloves, and protective clothing.


2. Add a few granules of the substance (if solid) or a few
   drops of the substance (if liquid) to a well in the test plate.
   If you are testing a solid substance in solution, add a few
   drops of the appropriate solvent and allow the solid to
   dissolve.


3. Add a few drops of the reagent and start the timer. Record
   any obvious changes in color in Table 22-2, noting the
   time required for the change to occur. After the change
   appears to be complete, continue observing for 15 to 30
   seconds to see if any further change occurs. For example,
   a sample may immediately turn a bright color that fades
   or changes color over a short period. Figure 22-2 shows
   our spot plate with several positive and negative tests.
   (We won’t tell you which reagents or which substances are
   shown; run your own experiment and see for yourself.)


4. Repeat steps 2 and 3 for all of your samples, recording
   the names or descriptions of samples that are not labeled
   in the table.

oALIpToN ACTIvITIES

If you have time and the required materials, consider

performing these optional activities:

• If you have access to a Munsell color chart, match the
  color of the positive test results you obtain as closely
  as possible to the standard colors, and compare
  your results to published color standards for the
  substances you tested.


• Test various household substances using one or more
  of the other presumptive test reagents described in
  the 183258 document referenced earlier. (Before you
  consider doing this, look up each of the chemicals
  used in each reagent and decide whether it is
  worth using that reagent, based on cost and safety
  considerations.)

FIGURE 22-2: A spot plate showing positive and negative results

for various substances