Illustrated Guide to Home Chemistry Experiments

334 DIY Science: Illustrated Guide to Home Chemistry Experiments

PCEDURERO FIGURE 19-1: A positive flame test for sodium
1.f you have not already done so, put on your splash I
goggles, gloves, and protective clothing.

2. Fill a test tube about half full of concentrated
   hydrochloric acid and place it in the rack.


3. Light the gas burner and adjust it to produce a small,
   hot flame.


4. Hold the loop at the tip of the flame and heat it until the
   loop adds no color to the flame.


5. Test the hydrochloric acid for purity. Dip the loop into
   the hydrochloric acid, allow it to drain momentarily, and
   then hold the loop at the tip of the flame. It should add
   no coloration to the flame. If color appears, particularly
   the intense yellow color of sodium, the hydrochloric acid
   is insufficiently pure. Replace it with purer acid.


6. Before you test each sample, verify that the loop is clean
   by holding it in the flame. If any color appears in the
   flame, clean the loop by dipping it in the hydrochloric
   acid and heating it. If necessary, repeat the acid rinse
   and heat until no color appears. (Hydrochloric acid
   reacts with any contaminants present on the loop
   to form chloride salts, which have low boiling points;
   heating the loop vaporizes the chloride salts, removing
   them from the loop.)

TABLE 19-2: Using flame tests to discriminate metal ions—observed data

Sample Observations

Sodium-free salt (example)

Medium yellow coloration, indicating presence of sodium; pale blue-violet

potassium coloration visible through cobalt glass

A. Barium

B. Boron

C. Calcium

D. Copper(I)

E. Copper(II)

F. Copper(II) halide

G. Iron(II)

H. Iron(III)

I. Lead

J. Lithium

K. Magnesium

L. Manganese

M. Potassium

N. Sodium

O. Strontium

P. Zinc

7. Test the first sample by touching the loop to the sample
   and holding it in the flame. If the sample is solid, dip the
   clean loop into the hydrochloric acid, allow it to drain
   momentarily, and then touch the loop to the sample. If
   the sample is liquid, dip the clean loop into the liquid.
   Record your observations in Table 19-2. If a sample does
   not produce a clear coloration, repeat the test using a
   larger amount of the sample.


8. Repeat step 7 for each of your samples.