Flame Test Lab for Lachsa Chemistry Students

Activity No. 3

Flame Tests

CA Standard 1j: Students know that spectral lines are the result of transitions of electrons between energy levels and that these lines correspond to photons with a frequency related to the energy spacing between levels by using Plank's relationship (E=hv).

Purpose: To be able to observe the colors emitted by the metallic ions when heated or subjected to flame.

Hypothesis: (make up your own)

Materials: Q-tips; water; crucible tongs; Bunsen burner; Crystals of lithium chloride, sodium chloride, potassium chloride, calcium chloride, strontium chloride, barium chloride, copper (II) chloride

Introduction:

When elements are heated to high temperatures, they may enter an excited state. In an excited state, the electrons move to higher energy levels. The changes in energy that occur when the excited electrons return to their ground state (lower energy level) causes the substance to be luminous or emit light. The observed colors or spectrum of the substance is caused by the set of visible wavelengths of light emitted. Since each element emits a unique set of wavelengths, emission spectra can be used as a tool to identify the elements.

One method used to demonstrate the emission spectrum of a substance is the flame test. Using this method, a small amount of a substance is heated and the characteristic glow of the substance is observed. In this experiment, you will develop a reference table which lists the flame color for each metal ion.

Procedure:

1. Dip a q-tip (cotton swab) in water. Dip the moistened q-tip into the lithium chloride so that a few crystals stick to the cotton. Put the crystals on the q-tip into the flame of the Bunsen burner. Observe the color of the flame and record it in your data table.

2. Repeat step 1 for each of the metallic chlorides (sodium chloride, calcium chloride, potassium chloride, strontium chloride, barium chloride, and copper (II) chloride). Be sure to record the color of each flame in your data table.

Data Table:

Flame Test Results

Compound Flame color

Lithium chloride

Sodium chloride

Potassium chloride

Calcium chloride

Strontium chloride

Copper (II) chloride

Barium