Atomic Spectra Answer sheet



Atomic Spectra Answer sheet

Computer number_____________________________

Group Members Names Role

_________________________ Leader (manages people and time, makes sure all participate)

__________________________ Recorder (keeps track of results and records lab report)

__________________________ Checker (makes sure all results are correctly reported)

Part I: Diffraction grating glasses:

Look at a variety of light sources and practice careful recording of your observations. Some suggested objects are the fluorescent lights above, an incandescent light (desk lamp), the computer screen, and sunlight (if available!)

Part II: Spectrometer Calibration

Before making measurements with the spectrometer, you must calibrate your instrument.

Note: Light is usually measured either in nm (nanometers) or Ǻ (Angstroms). A nanometer is 10-9 m while an Angstrom is 10-10 m. In this lab, record your values in nanometers. Note that you will see additional numbers (in the range of 1.7-3.4 ) on the top of the scale. You may ignore these numbers. The numbers that correspond to wavelength are on the bottom of the scale and are in the range of 350-750 nm.

Instructions: Calibrate your spectrometer using the information on the top of the device and the fluorescent lights in the lab room. You will see a very faint continuous spectrum along with bright emission lines.

You should see a bright green emission line at approximately 546 nm. Record the position of the green line that you see in the first row of the second column in the following table. Do the same for the 436 and 405 nm wavelengths and write down the color you see in the third column.

Fluorescent Tube Data

|Wavelength given on top of |Wavelength You Measured (nm) |Difference between your |Line Color |

|spectrometer (nm) | |wavelength and the given | |

| | |wavelength | |

|546 | | |Green |

|436 | | | |

|405 | | | |

Question: How will the information you just collected be useful when you observe other light sources? Think about error and exact positioning of lines.

Question: On the top of the spectrometer, it indicates that fluorescent lights should produce a spectral line at around 577 and 579 nm, in addition to the wavelengths shown in the first column of the table above. Do you see a spectral line near these wavelengths?

Question: Do you see any spectral lines at wavelengths that are not mentioned on the top of the spectrometer? If so, list them here and propose two possible reasons why you see them though they are not listed by the manufacturer on the top of the spectrometer. Of these two reasons, state which one you think is more likely and why.

Part III: Measurements of Hydrogen and another known gas

Answer the following questions:

1. Do you expect different elements such as hydrogen, helium, oxygen, and nitrogen to have emission lines that are the same or different from each other? Do you think all elements should have at least some lines in common, or do you expect them to be different for each element? Explain your reasoning.

2. Based on your results in the table for the fluorescent lights, how accurate (in nanometers) are the values for the locations of the spectral lines that you found. How precise (in nanometers) do you think your values are (are they plus or minus 2 nm for example, or 5 nm or 10?) Explain your reasoning below.

Now that you have calibrated our instrument, you are ready to make measurements.

Warning: The tubes require high voltage. Turn off the power supply before changing tubes. Do not touch the connections between the tube and the power supply while the power supply is turned on.

Instructions:

1. Begin by viewing the tube your instructor has identified as Hydrogen. Place it in the power supply unit. After the overhead fluorescent lights have been turn off, turn on the power supply unit and use the spectrometer to view the spectrum produced by the gas.

2. From the Insert tab on Word choose Shapes, then select the line symbol. Draw lines on the ruler below to show where you viewed lines. Right click on the line and choose Format AutoShapes, then select the color closest to what you see and adjust the weight of the line to approximate its intensity as seen in the spectrometer. On or below the lines you draw, write down the wavelength and the color of the lines you viewed.

3. Use the spectral charts in the lab room and the lines you drew on the ruler to fill out the table below the ruler.

4. Repeat steps using a second gas tube assigned to you by your instructor.

Element: _____Hydrogen___________

General color of light emitted by tube:___________________________________

[pic]

Ruler 1: Record the positions of the lines shown on the spectrum on the chart in front of room

[pic]

Ruler 2: Record the positions of the lines that you measured with your spectrometer

|Lines on spectral chart (Ruler 1) but not on Ruler 2. |Lines not on spectral chart (Ruler 1) but on Ruler 2. |

|Wavelength |Color |Wavelength |Color |

| | | | |

| | | | |

| | | | |

| | | | |

Element assigned by instructor: _______________

General color of light emitted by tube:___________________________

[pic]

Ruler 1: Record the positions of the lines shown on the spectrum on the chart in front of room

[pic]

Ruler 2: Record the positions of the lines that you measured with your spectrometer

|Lines on spectral chart (Ruler 1) but not on Ruler 2. |Lines not on spectral chart (Ruler 1) but on Ruler 2. |

|Wavelength |Color |Wavelength |Color |

| | | | |

| | | | |

| | | | |

| | | | |

Part IV: Unknown element

1. Describe how you would go about determining what elements are present in a heated gas by observing the spectral emission lines from the gas.

What kinds of difficulties might you expect based on what you have already done when you looked at the two gases in Part III?

Outline the procedure you will follow to identify an unknown gas sample.

2. Your instructor will give you an unmarked gas tube. Use the procedure you developed in question 1 to attempt to identify the gas. Record your data and include a data table. Explain the steps your group went through as you gathered data and compared it to known sources. Based on your data, tell what gas you think your group was given to identify. Remember to use the calibration information from Part II of the lab to increase the accuracy of your observations.

General color of light emitted by tube:____________________________

[pic]

Ruler 1: Record the positions of the lines you see on the spectrometer here.

Write a short report that includes:

Procedure

How you carried out the investigation

Data in table form

Discussion of how your element’s spectrum compares to known gasses

Your conclusion about what element you were given

Analysis of that conclusion, what evidence supports your claim, what evidence contradicts it

What could you do to improve your observations?

Conclusion question: (Individual response, attach to end of group report, remember this should be independent work) Astronomers say that stars are made mainly out of hydrogen and helium, but that all elements we know were created in stars by fusion or other processes. Explain how what you have learned in this lab might help astronomers understand the nature of stars.

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