DATE PERIOD NAMES

EXPERIMENT 18: FLAME TESTS FOR METALS

PURPOSETo observe and identify metallic ions using flame tests.

INTRODUCTION

JUST AS A FINGERPRINT IS UNIQUE TO EACH PERSON, THE COLOR OF LIGHT EMITTED BY METALS HEATED IN A FLAME IS UNIQUE TO EACH METAL. 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 EXCITED ENERGY LEVELS. FROM THESE EXCITED ENERGY LEVELS, THE ELECTRONS NATURALLY WANT TO MAKE A TRANSITION, OR RELAX, 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. A PHOTON IS COMMONLY REPRESENTED BY A SQUIGGLY LINE (SEE FIGURE 1). 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.

GROUND STATE

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 DIFFERENCES 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.

IN THIS LABORATORY ACTIVITY, THE CHARACTERISTIC COLOR OF LIGHT EMITTED FOR BARIUM, CALCIUM, CESIUM, COBALT, COPPER, LEAD, LITHIUM, MAGNESIUM, MANGANESE, NICKEL, POTASSIUM, SODIUM, AND STRONTIUM WILL BE OBSERVED.PRE-LAB ASSIGNMENT – IGNITING CHEMISTRY IN FIREWORKS

Fireworks capture our attention with their beautiful colors and controlled explosions, both of which link directly to fundamental concepts taught in basic chemistry classes. The media resources featured in this lesson provide a visually rich way to tie together spectral chemistry, combustion, and the nature of fire. Students watch a video segment and read text about the color of fireworks (particularly useful when following a chemistry lab in which powders of elements are placed over a flame to observe their spectral emission). They also watch a video segment and do an interactive activity on the mechanics of a firework, which leads to optional interactive activities for those wanting a slightly more advanced chemistry lesson involving chemical reactions. They wrap up by viewing video segments of many different types of fireworks and explaining the principles of chemistry and pyrotechnics that create all their glory.

Objectives Learn that the specific colors in a firework display are created when atoms of a particular

element or a combination of elements are energized by the firework's heat.

Learn that the shape of the firework display is determined by the shape and structure of one particular component inside the firework.

Discover that each component of a firework has a role in the timing, sound, and visual display that make up a firework.

Understand that the chemical reaction necessary for the ignition of a firework is an oxidation reaction in which energy is released by the combination of oxygen with other elements.

Understand that when the energy produced by the chemical reactions inside a firework is trapped in a small space, heat is created much more rapidly than it is dissipated, resulting in combustion that causes the firework material to burn.

Resources Fireworks! Making Color QuickTime Video

http://www.pbs.org/wgbh/nova/education/physics/fireworks-making-color.html

Fireworks! Lifting Charge QuickTime Video http://www.pbs.org/wgbh/nova/education/tech/fireworks-lifting-charge.html

Anatomy of a Firework Flash Interactive http://www.teachersdomain.org/resource/phy03.sci.phys.matter.fanatomy/

Pyrotechnically Speaking HTML Document http://www.teachersdomain.org/resource/phy03.sci.phys.matter.pyrotech/

Name That Shell HTML Interactive http://www.teachersdomain.org/resource/phy03.sci.engin.design.nameshell/

Pyrotechnics: It's Elemental HTML Interactive http://www.teachersdomain.org/resource/phy03.sci.phys.matter.kaboom/

On Fire Flash Interactive http://www.teachersdomain.org/resource/phy03.sci.phys.matter.onfire/

Part I: The Colors of Fireworks

1. Watch the Fireworks! Making Color video and type your answers to the following questions:

How are different elements used to make firework displays more enjoyable for spectators?

How does this relate to the lab activity in which elements were tested over a flame? (if the students have already done this in class)

What element is used to make your favorite color firework? Are some colors made by more than one element?

What advances have been made over the years in creating color in fireworks, and what advances can you imagine for the future?

Why does each element emit its own unique combination of spectral lines?

What causes the electrons to move up and down in energy levels within atoms in a firework?

2. Watch the Fireworks! Lifting Charge video and type your answers to the following questions:

What factors control the shape of a firework display?

How is a firework launched, and what other applications of this technology can you think of?

What components of a firework are designed for safety, for example, when launching near a crowd of people?

What advances have been made over the years in the structure and launching of fireworks, and what advances can you imagine for the future? Give examples.

3. Complete the Anatomy of a Firework interactive activity.

4. Read the Pyrotechnically Speaking document. Type your answers to the following questions:

How do particular elements determine the color of a firework and how does the structure of a firework determine its shape and timing?

Part II: The Chemical Reactions in Fireworks

5. Predict which chemicals are used to make the different colors of fireworks. Use the Pyrotechnics: It's Elemental interactive activity to check your predictions.

6. Complete the On Fire interactive activity. For each investigation, type your answers to the following: (1) Identify the key chemical principles that lead to fire: oxidation, combustion and chain reactions and (2) Explain what chemical reactions are involved.

Part III: Wrap-up 7. Complete the Name That Shell Interactive activity. Type your answers to the following: (1) Identify your favorite firework, (2) Explain how it is created, (3) Name the element that creates its color, (4) Name the shape of the "star" that is used to create the shape of the firework. (5) How many stages are needed to create the timing of the firework?PYROTECHNICS IS THE SCIENCE OF MATERIALS CAPABLE OF UNDERGOING SELF-CONTAINED AND SELF-SUSTAINED EXOTHERMIC CHEMICAL

REACTIONS FOR THE PRODUCTION OF HEAT, LIGHT, GAS, SMOKE AND/OR SOUND. PYROTECHNICS INCLUDE NOT ONLY THE MANUFACTURE OF FIREWORKS, BUT ITEMS SUCH AS SAFETY MATCHES, OXYGEN CANDLES, EXPLOSIVE BOLTS AND FASTENERS, AND COMPONENTS OF THE

AUTOMOBILE SAFETY AIRBAG.

MATERIALS

Barium chloride, BaCl2 • 2H2O

Calcium chloride, CaCl2 • 2H2OCesium chloride, CsCl Cobalt (II) chloride, CoCl2 • 6H2O

Copper (I) chloride, CuClCopper (II) chloride, CuCl2 • 2H20Iron (III) chloride, FeCl3 • 6H2O

Lead (II) nitrate, Pb(NO3)2

Lithium chloride, LiClMagnesium chloride, MgCl2 • 6H2O

Manganese (II) chloride, MnCl2 • 4H2ONickel (II) chloride, NiCl2 • 6H2OPotassium chloride, KClSodium chloride, NaClStrontium chloride, SrCl2 • 6H2OSpray Bottles (with 0.5 M Solutions of

Salts)Tirrill Burner or Meker BurnerCobalt GlassMatches

SAFETY FIRST ! ! !

IN THIS LAB, THE SOLUTIONS YOU WILL BE USING CONTAIN HARMFUL MATERIALS. AVOID SKIN CONTACT WITH THESE CHEMICALS. OBSERVE ALL PRECAUTIONS, ESPECIALLY THE ONES LISTED BELOW.

WEAR YOUR SAFETY GOGGLES AND APRON. DO NOT TASTE ANY OF THE SUBSTANCES OR TOUCH THEM WITH YOUR HANDS. DO NOT SPRAY THE CHEMICALS AT ANYONE. DO NOT SPRAY EXCESS CHEMICALS. IF YOUR FLAME GOES OUT, TURN OFF THE GAS IMMEDIATELY AND THEN RELIGHT! RETURN OR DISPOSE OF ALL MATERIALS ACCORDING TO THE INSTRUCTIONS OF YOUR TEACHER. WASH YOUR HANDS.

PROCEDURE

1. Light the Tirrill (or Meker) Burner.

2. Take one of the spray bottles filled with 0.5 M solution of chloride (or nitrate) salt and spray a fine mist into the flame of the burner. DO NOT OVERSPRAY. Observe the color of the flame.

3. Record your observations for the flame color produced by the metallic salt solution in the Data Table.

4. To cleanse the flame, spray a fine mist of distilled water until the previous flame color is no longer present.

5. Repeat steps 2-4 for each of the remaining metallic salt solutions.

6. After viewing the flame colors produced by MgCl2, NaCl, and KCl with the naked eye, view the flame colors through a piece of cobalt glass. Record your observations in the Data Table.

7. Using the spray bottle with the mixture of NaCl, and KCl, perform a flame test. View with the naked eye and through a piece of cobalt glass. Record your observations in the Data Table.

8. Repeat Steps 2-6 AS NEEDED using UNKNOWN I AND UNKNOWN II.

9. CLEAN UP your lab equipment, lab area, and return all materials.

10. WASH YOUR HANDS ! ! !

data tableION DETAILED OBSERVATIONS FLAME COLOR

BARIUM, BA2+

CALCIUM, CA2+

CESIUM, CS1+

COBALT, CO2+

COPPER, CU+

COPPER, CU2+

IRON, FE3+

LEAD, PB2+

LITHIUM, LI+

MAGNESIUM, MG2+

MANGANESE, MN2+

NICKEL, NI2+

POTASSIUM, K+

SODIUM, NA+

STRONTIUM, SR2+

MAGNESIUM, MG2+ (COBALT GLASS)

POTASSIUM, K+ (COBALT GLASS)

SODIUM, NA+ (COBALT GLASS)

POTASSIUM/SODIUM MIXTURE

POTASSIUM/SODIUM MIXTURE (COBALT GLASS)

UNKNOWN I

UNKNOWN I (COBALT GLASS)

UNKNOWN II

UNKNOWN II (COBALT GLASS)

QUESTIONS

1. Is flame coloration a test for the METALLIC ION OR for the CHLORIDE (OR NITRATE) ION?

2. List the ELEMENTS that produced the MOST easily identified colors.

3. Which ELEMENTS are LEAST easily identified? EXPLAIN.

4. Which ELEMENT produces the MOST intense color?

5. Identify the IONS in UNKNOWN I.

6. Identify the IONS in UNKNOWN II.

7. Would flame tests be useful for detecting metal ions present in a mixture of metal ions? EXPLAIN.

8. What is the purpose of using the cobalt glass in the identification of sodium and potassium? What differences did you observe in the flame, from the mixture of sodium and potassium, between your naked eye and the cobalt glass? Explain some reasons for the differences.

9. What difficulties may be encountered in the use of the flame test for identification?

10. Why do we see colors in the flame tests, and why are there different colors for different metal ions?

11. How does the flame test provide support for quantized energy levels? EXPLAIN YOUR ANSWER.

12. ELECTRON CONFIGURATIONS

WRITE THE SHORT-HAND AND NOBLE GAS ELECTRON CONFIGURATIONS FOR ALL OF THE IONS (EXCEPT NITRATE) USED IN THIS EXPERIMENT.HINT: TRANSITION METALS USUALLY LOSE S ORBITAL ELECTRONS FIRST.

ION SHORT-HAND ELECTRON CONFIGURATION NOBLE GAS ELECTRON CONFIGURATION