Materials Included In Kit

Additional Materials Required

Prelab Preparation

There are enough materials to set up 9 stations:

• Three stations can be designated as computer stations for the students to run through the virtual reality activity.
• Three stations can be set up for the phosphorescence activity.
• Three stations can be set up for the wet lab “Make Your Own Glow Stick Solution” activity.

Safety Precautions

Hydrogen peroxide is an oxidizer and skin and eye irritant. Sodium hydroxide solution is corrosive, very dangerous to eyes, and skin burns are possible. Much heat is evolved when sodium hydroxide is added to water. If heated to decomposition or in contact with concentrated acids, potassium ferricyanide may evolve poisonous hydrogen cyanide fumes. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information. 

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The resulting solutions may be disposed of according to Flinn Suggested Disposal Method #26b. The phosphorescent vinyl sheet and LEDs may be saved and reused for future labs.

Lab Hints

• Enough materials are provided in this kit for 30 students working in groups of 3 or for 10 groups of students. All three activities can reasonably be completed in one 50-minute class period. The Prelaboratory Assignment may be completed before coming to lab, and the data compilation and calculations may be completed the day after the lab.
• The phosphorescent vinyl sheet may be cut into three equal parts for the activity station.
• Student groups that are not at a station may work on any Open Education Resources available.
• The phosphorescent vinyl sheet has an adhesive backing and can be used as phosphorescent tape. It can also be easily cut into letters, shapes or smaller pieces with scissors.
• Store the phosphorescent vinyl sheet in its flat envelope or some other container that protects it from light. This will lengthen the life of the phosphorescent material in the sheet.
• Another means of displaying luminol’s luminescence is to take the two solutions (A and B), place them in spray bottles, and spray them at each other creating a luminescent cloud. The key to this procedure is to get the solutions into as fine a mist as possible. Caution: Do not spray the solutions toward anyone or in a manner in which they can be easily inhaled.

Answers to Prelab Questions

1. How does the OER simulation of the Bohr model of the atom relate to this lab’s topics?

Every atom has a unique emission spectrum because it has a unique electronic structure. The OER activity served as a means to illustrate the different parts that make up the atom: protons, neutrons and electrons. The electrons absorb energy from a source, are excited and release photons when relaxing back down to the ground state.

2. Observe the following visible spectrum values.

a. Which colors of visible light correspond to short wavelengths?

The colors of visible light that correspond to short wavelengths are violet and blue. Violet and blue have short wavelengths and high energy.

b. Which colors of visible light correspond to long wavelengths?

The colors of visible light that correspond to long wavelengths are orange and red. Orange and red have long wavelengths and low energy.

3. Refer to Figure 1 of the Background section. How is this figure similar to the emission spectra witnessed in the virtual reality activity?

Figure 1 is similar to the emission spectra witnessed in the virtual reality activity because distinct emission lines were observed, similar to those in Figure 1, depending on the element. Each spectrum tube had a specific spectral “finger print.”

4. Activity 3: Make Your Own Glow Stick Solution is a wet lab, which means that aqueous solutions and other chemicals will be mixed. What proper precautions should be taken before performing the lab?

All proper PPE of chemical splash goggles, apron and gloves should be worn. No food or drink are allowed on the benchtop during the experiment.

Sample Data

Activity 1: Atomic Spectra, A Virtual Reality Experience

The unknown spectrum tube in the virtual reality activity is air (a); it is considered a mixture. When a spectrum tube contains several gases, the resulting emission spectrum is a sum of the individual species’ spectra. The spectrum of air clearly has emission lines due to nitrogen and oxygen, which are the two largest components of air.

Activity 2: Phosphorescence

Students should have observed that the red LED did not cause the phosphorescent strip to glow, but the blue and white LED did cause the phosphorescent strip to glow. The blue LED has the required energy to promote electrons to an excited state, as does the white LED because it contains all of the energies of the electromagnetic spectrum.

References

Harvey, E. N., A History of Luminescence. The American Philosophical Society: Philadelphia, PA, 1957; p 5.

Huntress, E. H.; Stanley, L. N.; Parker, A. S., J. Chem. Educ., 1934, 11, 145.

Shakhashiri, B. Z. Chemical Demonstrations: A Handbook for Teachers of Chemistry, Vol. 1; University of Wisconsin: Madison, 1985; p 189.

Introduction

How can we study particles that are so small? Evidence-based experiments are the key to answering this question. In this activity-stations lab kit, you will have a chance to perform several experiments that lead to discovering the model of the atom. A virtual reality spectrum tube activity allows the study of emission spectra and the identification of an unknown. Observe the resultant glow when different LEDs are shone on a phosphorescent sheet. Finally, a quick mix of chemicals produces light also known as chemiluminescence—in a beaker. What do all of these experiments have in common? Let’s find out!

Watch the introductory video.

Concepts

• Atomic emission spectrum
• Structure of the atom
• Electron energy levels
• Electron transitions
• Phosphorescence
• Chemiluminescence

Background

Activity 1: Atomic Spectra, A Virtual Reality Experience

Rutherford’s famous “black box” experiment led to major discoveries of the structure of the atom:

• Most of the mass of the atom is concentrated in a very small, dense central area (later called the nucleus), which is about 1/100,000 the diameter of the atom.
• The rest of the atom is apparently “empty space.”
• The central, dense core of the atom is positively charged, with the nuclear charge equal to about one-half the atomic mass.

Work through the “Build an Atom Simulation” to familiarize with the structure of the atom. http://www.rsc.org/learn-chemistry/resource/res00001433/build-an-atom-simulation?cmpid=CMP00003366

The virtual reality activity in this lab provides a means to understand the structure of the atom by observing the emission spectrum of various elements in the gas phase. When electrical energy is supplied to the atoms in a spectrum tube, the atoms absorb energy and the electrons are promoted to excited energy levels. Once excited, the electrons have a natural tendency to drop back down to a lower energy level, emitting light of the appropriate wavelength and energy. The emitted light for a given transition is observed through a diffraction grating as a bright line in the emission spectrum of hydrogen. The relationship between the energy of light and its wavelength is shown in Equation 1.

∆E is the difference in energy between the two energy levels in joules, h is Planck’s constant (h = 6.626 x 10^–34 J•sec), c is the speed of light (c = 2.998 × 108 m/sec), and λ (lambda) is the wavelength of light in meters. When the allowed energy levels for the electron in the hydrogen atom were calculated, the results correctly predicted the wavelengths of visible light observed in the emission spectrum of hydrogen (see Figure 1).

Activity 2: Phosphorescence

Phosphorescence, also known as “glow-in-the-dark,” is the process of light emission that occurs when electrons that have been promoted to a higher energy level or state return (“relax”) back down to the ground state at a later time. The time interval between when the electrons are excited and when they relax is the primary difference between phosphorescence and other types of luminescence, such as fluorescence. While fluorescent materials return immediately to the ground state following excitation, phosphorescent materials relax at a slower rate. This allows for light to continue to be emitted even after the exciting source has been removed. This is sometimes referred to as the “afterglow.”

In both phosphorescence and fluorescence, a light source is shone on the material and a photon is absorbed. The energy from the photon is transferred to an electron, which makes a transition to an excited electronic state. From this excited state, the electron naturally wants to relax back to its ground state. This relaxation process varies depending on whether the material is fluorescing or phosphorescing. In phosphorescence, the excited electron makes a series of transitions to return to the relaxed ground state. It first makes a slow transition to a second excited state very close in energy to the initial excited state. From this second excited state, the electron makes the transition down to a lower energy level and emits a photon in the process. The characteristic afterglow of phosphorescence is due to the delayed emission that occurs as a result of the slow transition between the first two excited states. A minimum light energy is needed to overcome the energy threshold of a material and initiate phosphorescence. The red, orange, yellow and green LEDs have lower energy and are unable to cause the material to phosphoresce. In contrast, the blue and purple LEDs have high enough energy able to cause phosphorescence.

Activity 3: Make Your Own Glow Stick Solution

This part of the lab involves chemiluminescence. Chemiluminescence occurs when light is produced through a chemical reaction in a gas or in solution. The energy for light emission comes from a chemical reaction, usually involving considerable change in the composition of the chemiluminescent material. The appearance of colors when different metal salts are placed in the flame of a Bunsen burner are examples of a variation of chemiluminescence known as pyroluminescence. Out of a wide variety of “cool light” demonstrations, where little or no heat is produced, the use of luminol (3-amino-phthalhydrazide) has been one of the most popular.

Luminol was discovered to be luminescent 1928. Since that time, numerous procedures have been developed that produce light using luminol. Experimentation has demonstrated that for luminol to luminesce, an oxidizing agent, an alkaline pH and some type of catalyst (such as copper or iron compounds) are required. This procedure gives just that condition. Sodium hydroxide acts as a base and converts luminol into a dianion, which is oxidized by hydrogen peroxide to an aminophthalate ion. The aminophthalate is found in an excited state, which will decay to a lower energy state through chemiluminescence, and one of the products is the emission of light. This light has a wavelength of 425 nm, which is in the blue zone of the visible spectrum.

Experiment Overview

This is an atomic and electron structure activity stations lab. Spend about 8–10 minutes at each station, make observations and take notes in your lab notebook.

Materials

Prelab Questions

1. How does the OER simulation of the Bohr model of the atom relate to this lab’s topics?
2. Observe the following visible spectrum values.

1. Which colors of visible light correspond to short wavelengths?
2. Which colors of visible light correspond to long wavelengths?

3. Return to Figure 1 in the Background section. How is this figure similar to the emission spectra witnessed in the virtual reality activity?
4. Activity 3: Make Your Own Glow Stick solution is a wet lab, which means aqueous solutions and other chemicals will be mixed. What proper precautions should be taken before performing the lab?

Safety Precautions

Hydrogen peroxide is an oxidizer and skin and eye irritant. Sodium hydroxide solution is corrosive, very dangerous to eyes, and skin burns are possible. Much heat is evolved when sodium hydroxide is added to water. If heated to decomposition or in contact with concentrated acids, potassium ferricyanide may evolve poisonous hydrogen cyanide fumes. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron.

Procedure

Activity 1: Atomic Spectra, A Virtual Reality Experience

1. Click on the Atomic Spectra virtual reality activity.
2. Follow the screen prompts to observe the emission spectra of the spectrum tubes.
3. After viewing the emission spectra of all the known spectrum tubes, insert the unknown spectrum tube and observe its emission spectra.
4. The unknown spectrum is a mixture of gases. Select the best answer from the following options, and explain your answer based on the emission spectrum.

1. Air
2. Water vapor
3. Mercury and iodine

Activity 2: Phosphorescence

1. In a darkened room or dark area of the classroom, remove the phosphorescent vinyl sheet from its package.
2. Switch the three provided LEDs to the ON position.
3. Have one group member hold the phosphorescent vinyl sheet against a wall or solid surface.
4. One-by-one, bring the LEDs right up against the top of phosphorescent vinyl sheet and slowly drag the LED down the sheet. Make observations and collect notes in the lab notebook.

Activity 3: Make Your Own Glow Stick Solution

1. Prepare Solution A by adding 0.05 g of luminol and 25 mL of 5% sodium hydroxide solution to approximately 400 mL of distilled or deionized (DI) water. Stir to dissolve the luminol. Once dissolved, dilute this solution to a final volume of 500 mL with DI water.
2. Prepare Solution B by adding 0.3 g of potassium ferricyanide and 8 mL of 3% hydrogen peroxide to approximately 400 mL of DI water. Stir to dissolve the potassium ferricyanide. Once dissolved, dilute this solution to a final volume of 500 mL with DI water.
3. Set up the equipment as shown in Figure 3.

4. Turn down the lights. The room should be as dark as possible.
5. Pour Solutions A and B into the large funnel simultaneously. As the two solutions mix, chemiluminescence begins.
6. Consult your instructor for appropriate disposal procedures.
7. (Optional) Watch the conclusion video.