Name: ______Date: ______Period: _____

Introduction: The color of light emitted by an element heated in a flame is unique to each element. It is a diagnostic tool used in chemistry to help identify elements. In this experiment, the characteristic color of light emitted by calcium, copper, lithium, sodium, potassium, and strontium will be observed.

Background: When a substance is heated in a flame, the atoms absorb energy from the flame. This allows the electrons to be promoted to excited energy levels. From this excited state, the electrons will eventually drop back to the ground state. A photon is then emitted. The energy of this emitted photon determines the color of light observed in the flame.

Materials:

Safety Goggles

7 Cotton Swabs

Bunsen Burner

Matches

2 - 250mL Beakers

Water

Well Plate

Calcium Chloride (CaCl2)

Copper Chloride (CuCl2)

Lithium Chloride (LiCl)

Sodium Chloride (NaCl)

Potassium Chloride (KCl)

Strontium Chloride (SrCl2)

Unknown Chloride

Procedure:

1.  Fill both 250mL beakers halfway with distilled water.

2.  Collect a small amount of each sample in the well plate following the template.

3.  Obtain cotton swabs and place them in one beaker of water.

4.  Light the Bunsen burner.

5.  Dip the soaked swab into the first well making sure that some of the solid sticks to the swab.

6.  Hold the swab into the flame. Observe the color of the flame. DO NOT allow any of the solid chloride to fall into the barrel of the Bunsen burner.

7.  Immerse the swab in the other beaker of water to extinguish it.

8.  Record your observations in the data for the flame produced by this chloride.

9.  Repeat steps 5-8 for the other metal chlorides. Remember to record your observations for the color produced by each metal ion.

10.  Perform the flame test on an unknown metal chloride. Record its’ characteristic color and attempt to identify it.

Data:

Metal Chloride / Observations
Calcium Chloride (CaCl2)
Copper Chloride (CuCl2)
Lithium Chloride (LiCl)
Sodium Chloride (NaCl)
Potassium Chloride (KCl)
Strontium Chloride (SrCl2)
Unknown Chloride

Questions:

1.  Consider the following terms: quanta, ground state, excited state, atomic spectra. What do these terms have to do with this lab?

2.  Summarize the process that produces the colors seen in the flame test.

3.  What evidence is there from your results that the characteristic color observed for each compound is due to the metal ion in each case.

4.  Yule logs are commercially available that burn with a red and green flame. What two chemicals would produce this effect?

5.  The alkali metal cesium (Cs) and rubidium (Rb) were discovered based on their characteristic colors. Cesium is named after the sky and rubidium after the gem color. What colors of light do you think these metals give off when heated in a flame?

6.  Identify the unknown chloride. Was the flame test an adequate way to identify it? Why or why not?