Download experiment 18: flame tests for metals

DATE
PERIOD
NAMES
EXPERIMENT 18: FLAME TESTS FOR METALS
PURPOSE
To 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.
SUBSTANCE IS HEATED IN A FLAME, THE SUBSTANCE’S ELECTRONS ABSORB ENERGY FROM THE FLAME.
THIS
WHEN
A
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
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.
DOWN TO THE GROUND STATE.
GROUND STATE
THE
COLOR OF LIGHT OBSERVED WHEN A SUBSTANCE IS HEATED IN A FLAME VARIES FROM SUBSTANCE TO SUBSTANCE.
ELECTRONIC CONFIGURATION, THE ELECTRONIC TRANSITIONS FOR A GIVEN SUBSTANCE ARE UNIQUE.
THEREFORE,
BECAUSE
EACH ELEMENT HAS A DIFFERENT
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/phys
ics/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/phy0
3.sci.phys.matter.fanatomy/

Pyrotechnically Speaking HTML Document
http://www.teachersdomain.org/resource/phy0
3.sci.phys.matter.pyrotech/

Name That Shell HTML Interactive
http://www.teachersdomain.org/resource/phy0
3.sci.engin.design.nameshell/

Pyrotechnics: It's Elemental HTML
Interactive
http://www.teachersdomain.org/resource/phy0
3.sci.phys.matter.kaboom/

On Fire Flash Interactive
http://www.teachersdomain.org/resource/phy0
3.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 • 2H2O
Cesium chloride, CsCl
Cobalt (II) chloride, CoCl2 • 6H2O
Copper (I) chloride, CuCl
Copper (II) chloride, CuCl2 • 2H20
Iron (III) chloride, FeCl3 • 6H2O
Lead (II) nitrate, Pb(NO3)2
Lithium chloride, LiCl
Magnesium chloride, MgCl2 • 6H2O
Manganese (II) chloride, MnCl2 • 4H2O
Nickel (II) chloride, NiCl2 • 6H2O
Potassium chloride, KCl
Sodium chloride, NaCl
Strontium chloride, SrCl2 • 6H2O
Spray Bottles (with 0.5 M Solutions of Salts)
Tirrill Burner or Meker Burner
Cobalt Glass
Matches
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
WASH YOUR HANDS.
TEACHER .
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 TABLE
ION
DETAILED OBSERVATIONS
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
UNKNOWN I
UNKNOWN I (COBALT GLASS)
UNKNOWN II
UNKNOWN II (COBALT GLASS)
GLASS)
FLAME COLOR
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