djmpeterson.weebly.comdjmpeterson.weebly.com/uploads/1/2/6/7/12672666/lesson_6... · Web viewSetup: Dissolve the metal chloride salts in water (0.5 M works) (NaCl, CuCl 2, CaCl 2,

Doug Peterson

Chem 419

Atomic Structure and Models Unit: Lesson #6

Flame Lab (Inquiry)

HSCE:

· C1.1C: Conduct scientific investigations using appropriate tools and techniques (e.g., selecting an instrument that measures the desired quantity—length, volume, wseven, time interval, temperature—with the appropriate level of precision).

· C1.1E: Describe a reason for a given conclusion using evidence from an investigation.

· C1.1g: Based on empirical evidence, explain the reasoning used to draw a scientific conclusion or explanation.

· C2.4a: Describe energy changes in flame tests of common elements in terms of the (characteristic) electron transitions.

· C2.4b: Contrast the mechanism of energy changes and the appearance of absorption and emission spectra.

· C2.4d: Compare various wavelengths of light (visible and nonvisible) in terms of frequency and relative energy.

Learning Objectives:

· I can connect the relaxation and excitation of electrons to specific wavelengths of light.

· I can use specific wavelengths of light to calculate the energy generated when the electron returns to its ground state.

· I can explain why specific elements emit different colors of light.

· I can recognize the dual nature of light (waves and particles).

· I can utilize the specific variable of these mathematical models.

a. Wavelength

b. Frequency

· I can recall that electrons behave as particles (similar to light).

· I can recall that electrons can be excited causing the absorption and emission of specific colors of light.

· I can describe energy changes in flame tests for common elements.

· I can identify elements based upon their emitted light.

Materials:

· Materials:

· Day 1

· Unit PowerPoint

· Bohr Model Practice Worksheet

· Bohr Model Worksheet

· Electromagnetic Radiation Worksheet

· Day 2

· See the teachers guide for the lab materials needed.

Methods

Day 1

*These concepts are covered very heavily in Kelsey's unit plan. For this reason, this class period will be devoted to reviewing the concepts of electromagnetic radiation, the light spectrum, the idea of particles as waves, and the Bohr model of the atom.

1. Hand out the Bohr Model Practice Worksheet.

2. Use the PowerPoint to review the concepts of electromagnetic radiation, light spectrum, particles as waves, and the Bohr model of the atom.

3. Be sure to show students how to utilize the equation (E = hc/ λ)

a. There are two problems embedded into the PowerPoint that will be useful.

b. Students should complete these problems in their notes.

4. When you reach the Bohr model of the atom, practice constructing Bohr model atoms as a class.

5. When finished with the PowerPoint, pass out the Bohr model and electromagnetic radiation worksheets.

6. Allow the remainder of the hour to complete these worksheets.

7. They will become homework if the students do not complete them.

*This is simply a review. Students should have already learned about these concepts. Normally, this concept would take more than one day to complete.

Day 2

1. Have students get their homework from Day 1 out and obtain a copy of the lab.

a. Quickly go over the electromagnetic radiation worksheet, students will need to be able to calculate this to complete the lab.

2. Break students into their lab groups.

3. Allow the students time to read the labs safety and background information.

4. Once they have finished this, allow them to complete the pre-lab.

5. Go over the pre-lab as a class.

6. Take students into the lab.

7. Explain part one and two of the lab.

a. Part 1: You will be burning seven different salts and observing the colors of the flames.

i. DO NOT BURN THE Q-TIP, they do not need to be burned to produce a colored flame.

ii. There are seven stations set up (one for each salt).

iii. You will generate your own procedure and table for observations.

1. When developing your procedure, be sure to mention any safety precautions. You will only be able to use a Bunsen burner, q-tips, and dissolved salts. Don't forget to mention your disposal methods.

b. Part 2: You will mix salts to attempt to produce the purple color of Melvin's fireworks.

i. You will be developing your own recipe here.

c. Following this, you will complete some analysis questions which will be due tomorrow.

8. Allow students to begin.

9. There are numerous stopping points and there are some hazards in this lab, so it is very important to facilitate all activities.

10. When students are finished, have them clean up the lab and then allow them to finish their analysis questions.

a. Their labs are due on the following day.

Assessment

· Bohr Model Practice Worksheet

· Bohr Model Worksheet

· Electromagnetic Radiation Worksheet

· Lab Documents

· Facilitation

References

· See teacher Copy of lab.

NAME:_____________________

DATE:_____________________

HOUR:_____________________

This Lab May Go Down in Colorful Flames (Student)

· Problem/ Question

Which combination of chemicals is needed to produce a purple color in fireworks?

· Prior Knowledge

Atomic structure (composition of the nucleus and the space surrounding it)

Light and atomic spectra

Absorption and emission of excited electrons

· Safety

Be sure to wear goggles and an apron at all times

· Materials

Set of metal chloride solutions (NaCl, CuCl2, CaCl2, SrCl2, LiCl, CoCl2, BaCl2)

Bunsen Burner

8 – 10 Q-tips

Cobalt glass plates

· Background Information

For the past 25 year, The Firework Company has supplied our community with fireworks for our Independence Day celebration. For all 25 years, The Firework Company has been lead by Melvin Blank. After many years of service, Melvin finally decided to call it quits. He retired and promptly moved to Florida to spend the rest of his days soaking up the sun with his wife. Unfortunately Melvin took his “recipe” for his spectacular purple fireworks with him. The Firework Company has tried to contact Melvin, but as he spends all his time on the beach, he cannot be reached.

The Firework Company needs help! They have to learn how Melvin made his purple fireworks or this year’s firework display will be ruined. The Firework Company is willing to pay quite a hefty amount for the “recipe”.

You have learned quite a bit about Chemistry thus far, and our school could use the money. So, rather than wasting our time with lecture, we need you to determine the “recipe” of Melvin’s purple fireworks. We have gathered a few chemicals from the stockroom. CAN YOU FIND THE CHEMICALS THAT WILL MAKE PURPLE FIREWORKS?

· Pre-Lab: Unfortunately for you, Mr. Peterson wants to make sure that you have all the information that you need to complete this lab. So, before you can move on, you must complete the following pre-lab questions.

1. What happens to an electron when energy is absorbed?

2. What happens to the electron when it emits energy?

3. What is released when an electron emits energy?

4. What determines the color of the released particle?

STOP!!!! Teacher Checkpoint:__________

· Part 1: Before we can find Melvin’s “recipe”, we must first test the chemicals that we have.

You will be burning 7 different elements over an open flame and observing the colors of the flames. You will be given seven salts of elements: lithium, sodium, potassium, calcium, strontium, cobalt, barium, and copper. Each element is dissolved in a solution of its chloride salt.

There is a different solution at each of the seven lab stations. You will go around to all 7, perform the flame test using the procedure that you generate.

· Procedure (Develop your procedure here).

· Be sure to include safety pre-cautions.

· You will only have a Bunsen burner, dissolved salts, and q-tips to work with.

· Be sure to mention how you will dispose of waste.


· Observations (Make a table here to label the colors observed)


· Part 2: Now that you have observed the colors that are created when lithium, sodium, potassium, calcium, strontium, barium, and copper are heated over an open flame, it is your job to use these colors to determine the “recipe” for Melvin’s famous purple fireworks.

Before you just randomly put chemicals together, answer these questions:

1. Which elements must be put together to create Melvin’s purple fireworks?

2. Why did you choose these elements?


Now try out your “recipe”. Did it work?

· Analysis

1. Albert Einstein determined this equation: (ΔE = hc/ λ)

In this equation:

ΔE is the difference in energy between the two energy levels in Joules,

h is Plank’s constant (h = 6.626 × 10–34 J·sec),

c is the speed of light (c = 2.998 × 108 m/sec), and

λ is the wavelength of light in meters.

If the wavelength of a red spectrum line is 700 nm, how much energy does each photon of this light have? Show your work! (Notice that λ should be in meters)

If the wavelength of a purple spectrum line is at 400 nm, how much energy does each photon of this light have? Show your work! (Notice that λ should be in meters)

2. On the far ends of the visible spectrum of light, there exists ultraviolet (UV) radiation and infrared (IR) radiation.

- UV radiation is dangerous. UV radiation is located just past violet on the spectrum.

- IR radiation is much less dangerous. It is located just past red on the spectrum.

Based on what you calculated in question 1, explain why UV is more dangerous than IR:

3. The energy of visible light increases from the least energetic color, red, to the most energetic color, violet. List the elements used in the flame tests in increasing order of the energy of their emitted light.

· Discussion

4. What conclusion can you draw about the relationship between elements and the emission of light?

This Lab May Go Down in Colorful Flames (Teacher Guide)

· MI HSCE

· C1.1C: Conduct scientific investigations using appropriate tools and techniques (e.g., selecting an instrument that measures the desired quantity—length, volume, wseven, time interval, temperature—with the appropriate level of precision).

· C1.1E: Describe a reason for a given conclusion using evidence from an investigation.

· C1.1g: Based on empirical evidence, explain the reasoning used to draw a scientific conclusion or explanation.

· C2.4a: Describe energy changes in flame tests of common elements in terms of the (characteristic) electron transitions.

· C2.4b: Contrast the mechanism of energy changes and the appearance of absorption and emission spectra.

· C2.4d: Compare various wavelengths of light (visible and nonvisible) in terms of frequency and relative energy.

· Type of Inquiry

Guided

· Time

Setup: Dissolve the metal chloride salts in water (0.5 M works) (NaCl, CuCl2, CaCl2, SrCl2, LiCl, CoCl2, BaCl2) in the morning of the lab (or the night before). This will save class time and allow for more exploration by the students.

Lab: This lab should be relatively quick and allow for explanation following the laboratory. The entire lab should only take about 30 minutes; however, be prepared to spend the entire hour (just in case.)

· Educational Objectives

1. The learner will be able to connect the relaxation and excitation of electrons to specific wavelengths of light.

2. The learner will be able to use specific wavelengths of light to calculate the energy generated when the electron returns to its ground state.

3. The learner will be able to explain why specific elements emit different colors of light based upon their transition from higher energy to ground states.

· Concepts Addressed

Light and atomic spectra, atomic emission, and will also re-enforce the quantum mechanical model of the atom and electron configuration.

· Misconceptions

Students view an atom as a sphere, where the atoms orbit the nucleus, similar to the orbit of planets in the solar system. Students struggle with the concept that the location of electrons cannot be exactly determined at a given time. This lab will begin to breakdown this misconception. Students should see that if electrons are excitable, they cannot orbit the nucleus like the planets in a solar system (Cokelez, 2011).

· Prerequisite Knowledge

This activity will follow lecture on the quantum mechanical model of the atom, atomic orbitals, electron configuration, light and atomic spectra, and atomic emission. This lab will serve as a method for re-enforcing the significance of the excitation of electrons as well as how this relates to the equation (ΔE = hc/ λ).

· Teacher Background

Absorption and Emission of Light in a Flame

When a substance is heated in a flame, the substance’s electrons absorb energy from the flame. This absorbed energy allows the electrons to be promoted to higher energy levels. From these excited energy levels, the electrons naturally want to make a transition back down to the ground state. When an electron makes a transition from a higher energy level to a lower energy level, a particle of light called a photon is emitted.

An electron may relax all the way back down to the ground state in a single step, emitting a photon in the process. Or, an electron may relax back down to the ground state in a series of smaller steps, emitting a photon with each step. In either case, the energy of each emitted photon is equal to the difference in energy between the excited state and the state to which the electron relaxes. The energy of the emitted photon determines the color of light observed in the flame. Because colors of light are commonly referred to in terms of their wavelength, the following equation is used to convert the energy of the emitted photon to its wavelength (ΔE = hc/ λ).

In this equation:


h is Plank’s constant (h = 6.626 × 10–34 J_sec),



Wavelengths are commonly listed in units of nanometers (1 m = 1 × 109 nm), so a conversion between meters and nanometers is generally made.

The color of light observed when a substance is heated in a flame varies from substance to substance. Because each element has a different electronic configuration, the electronic transitions for a given substance are unique. Therefore, the difference in energy between energy levels, the exact energy of the emitted photon, and its corresponding wavelength and color are unique to each substance. As a result, the color observed when a substance is heated in a flame can be used as a means of identification.

The Visible Portion of the Electromagnetic Spectrum

Visible light is a form of electromagnetic radiation. Other familiar forms of electromagnetic radiation include γ-rays such as those from radioactive materials and from space, X-rays which are used to detect bones and teeth, ultraviolet (UV) radiation from the sun, infrared (IR) radiation which is given off in the form of heat, the microwaves used in radar signals and microwave ovens, and radio waves used for radio and television communication. Together, all forms of electromagnetic radiation make up the electromagnetic spectrum. The visible portion of the electromagnetic spectrum is the only portion that can be detected by the human eye—all other forms of electromagnetic radiation are invisible to the human eye.

The visible portion of the electromagnetic spectrum is only a small part of the entire spectrum. It spans the wavelength region from about 400 to 700 nm. Light of 400 nm is seen as violet and light of 700 nm is seen as red. According to the equation ((ΔE = hc/ λ), wavelength is inversely proportional to energy. Therefore, violet light (400 nm) is higher energy light than red light (700 nm). The color of light observed by the human eye varies from red to violet according to the familiar mnemonic ROY G BIV: red, orange, yellow, green, blue, indigo, and violet. As the color of light changes, so does the amount of energy it possesses.

The following table lists the wavelengths associated with each of the colors in the visible spectrum. The representative wavelengths are used as a benchmark for each color. For example, instead of referring to green as light in the wavelength range 500–560 nm, one may simply refer to green light as 520 nm light.

· Safety

Lithium chloride is moderately toxic by ingestion and is a body tissue irritant. Cobalt chloride is a possible carcinogen as fume or dust and is moderately toxic by ingestion; causes blood damage. Barium chloride is highly toxic by ingestion. Do not allow students to light the q-tips on fire. This is not necessary to observe the color. In fact, it is more obvious if the q-tip is not allowed to burn. If this does occur, fully extinguish the q-tips by immersing them in a beaker of water before discarding them in the trash to avoid trashcan fires. Wear chemical splash goggles, chemical-resistant gloves, and a chemical resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory.

· Materials, Preparation, and Disposal

At seven lab stations, students will be provided with:

1. A dissolved metal chloride salt (NaCl, CuCl2, CaCl2, SrCl2, LiCl, CoCl2, and BaCl2).

2. Q-tips

3. Bunsen burner

4. Cobalt glass plate

5. Waste container for disposal of q-tips

Solutions should be evaporated and added to solid metal waste containers for disposal. Be sure to wear goggles and a chemical resistant apron at all times. Wash hands thoroughly with soap and water before leaving the laboratory.

· Pre-lab Engagement/ Questions

1. What happens to an electron when energy is absorbed?

The electron is excited and is promoted to a higher energy level.

2. What happens to the electron when it emits energy?

The electron makes a transition from a higher energy level to a lower energy level (ground state.

3. What is released when an electron emits energy?

A photon.

4. What determines the color of the released particle?

The wavelength of the emitted photon.

Students should be allowed to work through this portion of the lab in their lab groups. There is a stop built into the lab, the instructor should then discuss this portion of the lab with either each group or with the entire class. Now students should have the right frame of mind for the lab.

· Procedure/ Data

Student information will be given in italics. The background will be read prior to the pre-lab. Following class discussion of the pre-lab, students will begin the lab.

Background Information

For the past 25 year, The Firework Company has supplied our community with fireworks for our Independence Day celebration. For all 25 years, The Firework Company has been lead by Melvin Blank. After many years of service, Melvin finally decided to call it quits. He retired and promptly moved to Florida to spend the rest of his days soaking up the sun with his wife. Unfortunately Melvin took his “recipe” for his spectacular purple fireworks with him. The Firework Company has tried to contact Melvin, but as he spends all his time on the beach, he cannot be reached.

The Firework Company needs help! They have to learn how Melvin made his purple fireworks or this year’s firework display will be ruined. The Firework Company is willing to pay quite a hefty amount for the “recipe”.

You have learned quite a bit about Chemistry thus far, and our school could use the money. So, rather than wasting our time with lecture, we need you to determine the “recipe” of Melvin’s purple fireworks. We have gathered a few chemicals from the stockroom. CAN YOU FIND THE CHEMICALS THAT WILL MAKE PURPLE FIREWORKS?

Following class discussion of the pre-lab, students will begin the lab.

Part 1: Before we can find Melvin’s “recipe”, we must first test the chemicals that we have.

You will be burning 7 different elements over an open flame and observing the colors of the flames. You will be given seven elements: lithium, sodium, calcium, strontium, cobalt, barium, and copper. Each element is dissolved in a solution of its chloride salt.

There is a different solution at each of the seven lab stations. You will go around to all 7, perform the flame test using the procedure that you generate.

Here students will develop their own procedure and observation table for testing their dissolved chloride salts.

Procedure (Develop your procedure here)

Sample student procedure.

1. Be sure to wear goggles and a chemical resistant lab coat at all times.

2. Carefully start the Bunsen burner.

3. Dip a q-tip in a dissolved salt.

4. Expose the q-tip to the open flame of the Bunsen burner.

5. Observe and record the color of the flame.

6. Allow the flame to burn out and dispose of the q-tip in the proper waste receptacle.

Observations (Make a table here to label the colors observed)

Sample student observation table.

Metal ion

Color of Flame

Sodium

Yellow

Lithium

Red

Strontium

Red

Calcium

Orange

Barium

Green/ Yellow

Copper

Blue/ Green

Cobalt

White

Now that students have a good grasp of the colors observed with the seven salts, they should be able to figure out how to create a purple color.

· Part 2: Now that you have observed the colors that are created when lithium, sodium, potassium, calcium, strontium, barium, and copper are heated over an open flame, it is your job to use these colors to determine the “recipe” for Melvin’s famous purple fireworks.

Before you just randomly put chemicals together, answer these questions:

3. Which elements must be put together to create Melvin’s purple fireworks?

Strontium (or lithium) and copper.

4. Why did you choose these elements?

Strontium and lithium produced a red color, copper produced a blue color. Mixing red and blue will give us a purple color.

· Analysis

1. Albert Einstein determined this equation: (ΔE = hc/ λ)

In this equation:


h is Plank’s constant (h = 6.626 × 10–34 J·sec),



If the wavelength of a red spectrum line is 700 nm, how much energy does each photon of this light have? Show your work! (Notice that λ should be in meters)

E=((6.626x10-34J·sec)(2.998x108m/sec))/ (700nm/1x109nm)= 2.83 x 10-19 J

If the wavelength of a purple spectrum line is at 400 nm, how much energy does each photon of this light have? Show your work! (Notice that λ should be in meters)

E=((6.626x10-34J·sec)(2.998x108m/sec))/ (400nm/1x109nm)= 4.96 x 10-19 J

2. On the far ends of the visible spectrum of light, there exists ultraviolet (UV) radiation and infrared (IR) radiation.

- UV radiation is dangerous. UV radiation is located just past violet on the spectrum.

- IR radiation is harmless. It is located just past red on the spectrum.

Based on what you calculated in question 1, explain why UV is more dangerous than IR:

It has much more energy.

3. The energy of visible light increases from the least energetic color, red, to the most energetic color, violet. List the elements used in the flame tests in increasing order of the energy of their emitted light.

Lithium (or strontium), Strontium (or lithium), Calcium, Sodium, Copper, Barium (or Cobalt), Cobalt (or Barium).

· Discussion

4. What conclusion can you draw about the relationship between elements and the emission of light?

Student answers will vary, but they should mention that the higher the energy level the element is in will result in less energy because it releases less energy when it returns to its ground state. For example, Lithium emits lower energy than cobalt, which occupies a higher energy level.

· References

Chemistry (1993). Addison-Wesley. Chapter 4: Atomic Structure (p. 67-84.)

Chemistry (1993). Addison-Wesley. Chapter 11: Electrons in Atoms (p. 245-270.)

ChemSource (2010). Atomic Structure. Mary Virginia Orna Department of Chemistry at the College of New Rochelle. New Rochelle, NY.

Flinn Scientific (2007). Flame Test Kit: Student Laboratory Kit. In Flinn Scientific, Inc. Chem Fax. Catalog No. AP5607. Batavia, IL: Flinn Scientific.