Download Part 1: Elements and light

Name: ____________________________ Period: _____ Date: ___________________________
Stellar spectra
Inquiry Questions:
1. Why do objects appear the color they are (why is something red, red?)
2. Do objects that have a color give off (not reflect!) all wavelengths of light or just
certain ones? Explain.
3. What is a spectrum and what info does it tell you?
Part 1: Elements and light
Materials: salts
flame
Procedure:
1. I’m going to put certain salts into a flame and you need to record the appearance
of the powder and the color of the flame
Data:
Salt:
Strontium Chloride
Formula
CuCl2
CuSO4
Sodium Bicarbonate
NaHCO3
Sodium Chloride
LiCl
Barium Chloride
Potassium Chloride
CoCl2
Calcium Chloride
Appearance dry
Flame color
Conclusions:
1. Did any have the same color? Which ones?
2. Does it seem to be the first part of the chemical formula or the second part that
decides the flame color (is it the calcium or the chloride)? Explain.
What color would you predict for:
3. Potassium nitrate
Potassium sulfate
4. Calcium nitrate
Cobalt carbonate
5. How is the colored light produced? This really involves 2 things we studied this
year…electrons/energy levels (pg. 107) and star color (pg. 669).
6. Is each element unique in the color it gives off? Explain.
Part 2: Stellar spectra
Background:
We are going to look at some spectra (plural of spectrum) of light that certain
elements give off. We can measure them using a spectroscope, which has a diffraction
grating, which is a small piece of plastic with slits cut in it.
What you are seeing is called a bright line or emission spectrum. It represents
the wavelengths of light given off by each element. The opposite (all light with a few
dark bands in the same place) is called a dark line or absorption spectrum and
represents wavelengths of light absorbed by that element when white light shines
through it.
Materials: gases
diffraction gratings
colored pencils
Procedure:
1. Look at the tube and draw the spectrum you see. Try to be as accurate as possible
about the spacings/numbers. For the description, write the number of lines,
colors and numbers. For example, 1 purple line at 7, 2 blue/green ones at 5.8
Data:
Light source/element
Spectrum:
Describe:
White light (outside)
7
6
5
4
Light bulb
7
6
5
4
Fluorescent light
7
6
5
4
Hydrogen
7
6
5
4
Helium
7
6
5
4
7
6
5
4
Neon
Conclusions:
1. Describe what happens to waves during diffraction. (pg. 473)
2. Why are the spectra from different gases, different? (what is happening to the light
to make it look different)
3. Describe how a scientist can tell what elements a star is made of .
4. How are the spectra like fingerprints?
5. What would our star’s spectrum most likely look like? You can draw or describe,
but please use numbers for a scale.
Part 3: More spectroscopy
Procedure:
1. Cut out the 4 unknown stars (A, B, C, D) You can either separate them (but make
sure they’re labeled or keep them as one “chunk” and just fold over the ones
you’re not using. You can also color the lines, if you wish.
2. Hold each unknown star next to each element on the figure on the next page. Note
in Data Table 1 the elements present.
3. Use Data Table 2 to find the stellar class and temperature of each star. Note this in
Data Table 1. Strong lines are ones that are thicker. Weak lines are ones that
are thinner.
4. Use the HR diagram provided to find the color of each star. Note this in
Data Table 1.
Data Table 1:
Star: Elements present:
A
B
C
D
Stellar class:
Temperature:
Color:
Data Table 2:
Stellar class:
O
B
A
F
G
K
M
Temperature:
> 25,000 K
11,000 - 25,000 K
7,500 - 11,000 K
6,000 – 7,500 K
5,000 – 6,000 K
3,500 – 5,000 K
< 3,500 K
Elements present:
Helium and weak hydrogen lines
Helium and strong hydrogen lines
Very strong hydrogen lines, others present
Weak hydrogen lines, others present, esp. calcium and iron
Similar to F, weaker lines, stronger calcium
Metals (like iron, mercury) some molecules
No elements, strong molecules
Conclusions:
1. Can you tell the type of star (dwarf, main sequence or giant) from the stellar class?
2. Look at your HR diagram. What stellar class is the Sun?
3. The sun is class… because…
Describe what the spectrum would look like for a
4. Blue Giant
5. Main sequence blue star
6. Main sequence orange star
7. Red Giant
8. White dwarf
Giant stars get hot enough to make metals in their cores, while main sequence do not
get that hot.
9. How can you tell the spectrum of a main sequence red from a red giant? Could
they be different classes?
Sometimes the lines don’t fit the usual pattern. They are spaced apart the same, but
shifted towards one end of the spectrum.
10. What is this shift called (there are 2)?
11. What does it tell you about the star?
12. Why does it shift (what is happening to wavelength and what’s this called)?
13. Compare star B and D. how are they different and what does this mean?
Sometimes the lines are in the right place, but are thicker than usual. This may
mean it is spinning faster than usual.
14. Compare stars B & C. What do you notice and what does this mean?
Cut out the 4 unknown stars (A, B, C,
D) below. You can either separate
them (but make sure they’re
labeled or keep them as one
“chunk” and just fold over the ones
you’re not using. You can also
color the lines, if you wish.
Hold each unknown star next to each
element on the figure to the left.
You may have to move them a little
to see the match. Note in Data
Table 1 the elements present.