Here you will find material for Experiment 9 - Light From Atoms. This includes detailed guides for the pre-lab, data sheet, post-lab, and quiz questions. Experiment will have you observe light and use a spectroscope. Remember, the lab may change or be modified from semester to semester!

Experiment 9 is broken up into three main parts - A. Flame Tests, B. Using the Spectroscope, and C. Atomic Spectra

A. Flame Tests

In Part A, your TA will put different metal chloride solutions into an open flame. You will note your observations, specifically the color of each.

B. Using the spectroscope

Part B will have you use a spectroscope. You will use it to observe the fluorescent ceiling light for calibration. The image to the right illustrates the entering light being separated and gives you an idea of what’s happening as well as what you should observe.

Once calibrated, you will use the spectroscope to observe an incandescent lap. This will be done with and without placing a piece of blue glass between the lamp and the spectroscope.

c. atomic Spectra

This part will have you observe a hydrogen discharge tube. DO NOT TOUCH IT. You will then observe the a sodium flame test and compare it with what you saw for the hydrogen discharge tube.This section will be important in your calculations.

CALCULATOR (LINK)

A scientific calculator is needed for calculations on quizzes. Some labs have calculations that need to be turned in before leaving.

LAB GOGGLES (LINK)

Required eye protection. Must be worn at the start of the experiment and until leaving

COMBINATION LOCK (LINK)

A combination lock is required to lock your equipment drawer for the semester.

what to expect

The information provided below are things you will need to know and understand to complete this experiment successfully. We have also included parts of the lab that may give you difficulties, potential bottlenecks and workarounds so you can finish the experiment efficiently. Remember, the information given by TA should have the highest importance and supersedes all information provided on this page.

bottlenecks

This experiment can be completed relatively quickly. However, it may drag on much longer because of the difficulty for many to correctly observe what is expected.

Repeat Tasks

Because many people may have trouble seeing anything or seeing the “correct” observations, have multiple lab partners observe with their own spectroscope. Accurate observations are very important since many are used to do calculations.

• Speed of Light (c) = 3.0 e8 m/s

• Plank’s Constant (h) = 6.63 e-34 Js/photon

• Rydberg’s Constant (R) = 3.25 e15 Hz

• Speed of light (c) = Frequency (v) x wavelength (λ)

• Energy (E) = hc/λ or hv

Observations

Be careful with your observations. The numbers you obtain from the spectroscope will affect the calculations you make in this experiment. Have multiple lab partners observe and compare your values.

calculating frequency & energy level

In part C, you will observe a hydrogen discharge tube using a spectroscope. Using the colors you observe and wavelengths, you can then calculate the frequency by rearranging the speed of light equation.

Speed of light (c) = Frequency (v) ÷ wavelength (λ) —> v = c / λ

With the frequency and understanding that it’s from hydrogen, you plug in frequency into the frequency equation that uses Rydberg’s constant. This will enable you to calculate the excited energy level and energy change and energy.