2. Have the instructor light
your lab burner (Bunsen burner). Adjust the flame until it is totally blue. Look through the diffraction grating at the slit in the board. Have another team member move the lab burner so that you can see the brightest possible light from the
burner in the slit.
3. Obtain labeled bottles of
salts and write the chemical formula in a table in your lab notebook. Also obtain
a labeled bottle of an unknown salt. Recall that salts are combinations of metals
and a non-metal, or a metal and a polyatomic anion. Emission spectra that you
will be looking through the diffraction grating for will look like bars of colored light.
4. Now divide the work into three
A. One student will look through
the diffraction grating.
B. Another will use the white
card with the black line on it to mark the place where the student in A sees a spectral line (or light bar).
C. The third student will take
the salt and hold it into the flame.
Be very careful not to spill the salt into the Bunsen
burner. If you do spill salt into the Bunsen burner, all of your observations
that follow that accident will be affected.
5. Once all the materials are
assembled, the apparatus is set up and the burner has been lit, it’s time to turn out the lights. Student A observes the burner flame through the diffraction grating and slit. Student C should take a spatula,
dampen it slightly, and dip it into the small container of one of the salts so that a small amount clings to the tip. Student C then eases the salt on the tip of the splint or spatula into the flame. Be sure to ease the salt into the flame a few centimeters from the top of the burner
and on the side of the flame that is closest to the slit in the black card. The
idea is to get the salt into the flame without allowing the spatula into the flame.
If the spatula gets too hot, it will emit spectra (light cars) that will interfere with your observations and measurements. Once student C sees a color change in the flame, student C should hold the spatula
steady and not move it further into the flame. Be careful not to allow any of
the salt to drop into the burner as this will contaminate the burner and ruin your results for other salts.
6. Student B will hold the white
card with the vertical black line behind the meter stick that is forming the top of the “T”. Student A will look through the diffraction grating, locate the colored spectral line, and will have student
B move the white card until the line on the white card is directly in line with spectral line.
Student C can now remove the salt from the flame. Then, while student
B continues to hold the card in place, the team will use the flashlight to determine the distance from the slit to the spectral
line. This distance and the color of the spectral line should be recorded in
a table in your lab notebook. The name of the student performing each job should
also be recorded.
7. Repeat steps 5-6 with the
other salts but changing jobs so that no student has the same job a second time. Every
student in each group should do each job at least once.