Electrons and Light Flame Test Lab

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“Where does the violet tint end and the orange tint begin? Distinctly we see the difference of the colors, but where exactly does the one first blending enter into the other. So with sanity and insanity.” Herman Melville (1819 - 1891) Electrons and Light Lab

Introduction:

As electrons move between

excited states

and

ground states

, they emit distinct

wavelengths

of light. Some of these wavelengths fall in the visible color range and can be seen and therefore tested with the naked eye. Metal atoms, when placed in a flame, emit energy in the visible color range, and can therefore be identified using

flame tests

.

Pre-lab Discussion: Define the words found in bold in the introduction. ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ Purpose:

To understand and apply a flame test to the identification of metallic salts.

Question:

What color does each metallic salt sample emit in a flame test? Can these colors be used to identify an unknown sample?

Hypothesis: ________________________________________________________________________ ________________________________________________________________________ Procedure:

First make sure that you have a clean flame test wire. Do this by holding the metal loop in the hottest part of the Bunsen burner flame. If it is clean, there should be no change in the color of the flame when the metal loop is put in it. If it is not clean, clean it by dipping it into the concentrated acid provided, then holding the loop in the Bunsen burner flame. Repeat this cleaning until there is no more change in the color of the flame. The next job is to do your flame tests. Dip the flame test loop into one of the known test solutions, and then hold the metal loop in the hottest part of the Bunsen burner flame. Make a note of the

color

of the flame on your

Flame Test Chart

.

Clean the flame test wire, and then test another known test solution. Keep going until you have recorded the color of all of the known solutions. Get your results checked, then flame test the unknown solution and record the flame test results.

Data:

Flame Test Chart barium calcium copper lead potassium sodium Unknown flame: ______________________

Conclusion:

Answer the following questions in complete sentences. Attach your answers to this packet.

Due Thursday!

1.

2.

3.

4.

Why do you think the chemicals have to be heated in the flame first before the colored light is emitted? Colorful light emissions are applicable to everyday life. Where else have you observed colorful light emissions? Are these light emission applications related? Explain. Suppose you were a firefighter and you were called to a chemical plant fire. Upon arrival you see a bright violet/purple flame. What chemical would that tell you is burning? A fireworks employee works in a lab that designs fireworks. He wants to create a firework display that burns blue, red, and orange. If you were helping, what chemicals from the data above would you recommend? o o o o NaCI, CuSO CuSO Sr(NO 4 KCI, CuSO 3 ) 2 4 4 , and Fe(NO , KCI, and Fe(NO , and NaCI , CuSO 4 3 ) 3 3 ) , and NaCI 3

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