FLAME TESTS LAB
Objective: To observe the relationship between various elements and their emission spectrum.
Introduction: Flame tests provide a way to qualitatively test for the presence of specific elements by seeing colored flames. The heat of the bunsen burner excites the electrons in the atom, and this energy is released as the electrons “fall back” to their ground states. The color we see is a combination of the visible wavelengths of light emitted by the atoms.
If you have a spectroscope you can also make quantitative observations. A spectroscope can be used to see a pattern of narrow lights called an emission (bright-line) spectrum. The actually wavelengths of the spectrum serve as a quantitative test to determine atoms identities. Each element has a different “pattern” of electrons so it will show a different combination of colors.
In this lab, you will perform flame tests on seven different elements. You will use your observations to identify an unknown solution.
1, Why do we see colors in the flame tests?
We see colors in the flame tests because of the heat from the flame excites the electrons and causes it to move to another shell, the energy is released once the electrons “fall back” to their ground state. The color we see is a combination of a visible wavelength that produces the visible light that we see. Each element has a different “pattern” of electrons. So the color combination may be different.
2, How will we be testing the substances qualitatively?
We will be testing the substances qualitatively by observing the flame colors.
Materials: Safety goggles, wood splints, tongs/tweezers, Bunsen burner, test tubes with various compounds
1, Safety goggles must be worn at all time
2, Many of these salts are toxic. If you come into contact with any of the compounds make sure to notify the teacher and wash the contacted area thoroughly. Wash your hands before leaving the lab!
1, Light the Bunsen burner (turn the gas on so you can just hear it, then use the striker)
2, Place the wood splint for each compound into the flame using tongs or tweezers- ONE AT A TIME!
3, Take note of the color of the flame and return the wood splint to the solution.
4, CLEAN UP YOUR STATION! Carefully put the stoppers back on the solutions! Make sure the station looks like it did when you started! Let me know if you need new splints!
5, Wash your hands thoroughly before leaving the laboratory
Data Table: make a section of your lab labeled Data Table and make a data table similar to the one below to record your observations.
|Compound||The color of Flame (qualitative)||Wavelengths of light (in Å) (quantitative)|
|Barium Chloride||Orange||5900 – 6200A|
|Calcium Chloride||Red||6200 – 7500A|
|Copper (II) Chloride||Green||4950 – 5700A|
|Lithium Chloride||Violet||3800 – 4500A|
|Potassium Chloride||Orange||5900 – 6200A|
|Strontium Chloride||Red||6200 – 7500A|
Discussion and Analysis: (In a section labeled Discussion and Analysis answer the following questions in complete sentences)
1, How do your results from the flame test provide support for quantized energy levels? Explain your answer.
By heating the compound, the electrons got excited and jump to a higher energy. At the electrons “fall back” to their ground state, they emit energy (photon). The different element has a different pattern of electrons, therefore it has a different energy level. While releasing the energy, they also produce visible light as a result of a combination of visible wavelengths. This allows us to see the colors of the flame (qualitative data). The result collected from the flame test provide support for quantized energy levels as it provides the color for different compound and allowed us to look up the wavelength of different light color.