Spectral Lab: Honors Chem
Introduction:
An ecology student is doing an experiment on some metal ions that she extracted from the soil at
the bottom of a local harbor. In the laboratory, the student injects the metal ions into a hot flame.
Energy from the flame excites the electrons of the metal ions and boosts the electrons to a
higher energy level. When they fall back to their home energy level, they give off energy in the
form of light. As we know, each atom produces a specific set of colors at wavelengths that are
characteristic to that atom.
The student observes the light given off by the metal ions in the flame through a diffraction
grating. The diffraction grating spreads the light into a line spectrum. The student observes that
the line spectrum has wavelengths of 563 nm and 615 nm. The student compares this to a chart
of known metal line spectra, and determines that the metal is tin. The student is able to advise
the harbor that a type of paint they are using is producing this toxic ion in the water.
This process of using line spectra to identify unknown elements is very helpful, and is what you
will be doing in your activity today.
You will:
-familiarize yourself with line spectra of different elements
-relate wavelength number to color of line spectra
-use this knowledge to identify what gas is in fluorescent light
Pre-Lab Questions: (on your own paper)
1. What instrument will you use to view/separate colors of light and identify their wavelengths?
2. When atoms are heated and emit light, what characteristic of light allows you to tell one atom
from another?
3. Why must you avoid touching gas spectrum tubes?
Hypothesis: What gas do you think is present in fluorescent light? (on your own paper)
Procedure:
1. Obtain your diffraction grating.
2. Go outside and observe incandescent/visible light. Sketch results in the observation section.
3. Now observe the light from each of the labeled gas spectrum tubes. Record the line spectra,
including the wavelength for each color, in your observations section.
4. Now raise your diffraction grating and look at fluorescent light. Look carefully at the line
spectra, and try to ignore any color you see in the background. Record the line spectra, including
the wavelength for each color, in your observations section.
Hint: make sure you record the correct units for wavelength. Check your diffraction grating to ensure accuracy.
Please record all observations on your student data sheet.
Analysis Questions:
1. Compare your observed wavelengths with the actual values you recorded in your table. Are
they consistently higher, lower, or similar? Note the lines you did not see.
2. What is the gas inside the fluorescent tube? Support your conclusion with data from the table
and your observations.
3. Could you successfully complete this experiment if you were color blind?
4. Why do you think some of the spectral lines observed were not visible to you?
5. Why is there concern about breakage and improper disposal of fluorescent bulbs?
Write a conclusion:
Include results and explain how the lab is connected to the atom and its electrons.
Line Spectra for Elements
Student Data Sheet:
Observations:
Sketch the spectrum of the incandescent/visible light here:
Sketch the line spectra of the gases you observed here:
(record the specific wavelength for each color)
Gas:
Gas:
Gas:
Gas:
Sketch the line spectra of the fluorescent light here: (record the specific wavelength for each color)
In the table below, enter the color and observed wavelength from the line spectra for each of the
known gases.
Element
Hydrogen
Helium
Mercury
Neon
Colors
Wavelength