Green Chemistry – Colors in Flames
Have you ever observed fireworks in many different colors? Have you ever
wondered why?
The different colors of the flames of fireworks produced when energy is emitted
from the electrons. Electrons contain chemical energy in discrete
amounts. Energy can be added or released only in discrete amounts, or packets.
When electrons release energy, we see it as light. The color of the light depends
on the amount of energy released from the electrons.
Chemical energy is released through combustion of natural gas in the flame of a
Bunsen burner. Solutions containing metal salts are introduced into the flame in
tiny droplets. The electrons of the metal salts are excited by absorbing energy
from the flame. The electrons return to their ground state and the absorbed
energy is released. The electrons in different metals absorb and release energy
in different discrete amounts. The different colors come from the different
discrete amounts of energy released. Different metals show different flame
colors.
Learning Objectives
Students will perform a flame test on mineral salts, record observations and
report results.
Materials
Fisher burner (or Bunsen burner)
Striker
1 molar solutions of the following salts: CaCl2 CuCl2 LiCl2 NaCl SrCl2
Experimental Apparatus pictured below
Bunsen Burner Salt Solution Figure 1. Experimental Apparatus
Siena College Green Chemistry Institute Lucas Tucker, Michale O’Brien, Ann Klotz Page 1 Hazard Information
Chemical Name
Calcium chloride (aq)
Copper chloride (aq)
Potassium Chloride
Sodium chloride (aq)
Strontium chloride (aq)
Health Hazard
Low hazard
Harmful if
swallowed,
skin irritant
Low hazard
Low hazard
Irritant
Physical
Hazard
Low hazard
Low hazard
Environmental
Hazard
Low hazard
Moderate
Low hazard
Low hazard
Low hazard
Low hazard
Low hazard
Low hazard
Waste
Student will not dispose of any waste from this experiment. All solutions will be
saved for later use.
Procedure
1. Put on safety goggles
2. Your teacher will assemble the apparatus for this experiment. Do not
change the assembly unless instructed to do so by you teacher.
3. Turn on the gas and then light the Bunsen burner with a striker or match
4. Put the end of the fine tube into distilled or deionized water.
5. Observe the color of the flame and then record your observations.
6. Now move the end of the tube into a solution containing a metal salt and
water.
7. Pump air into the large tube. This causes tiny drops of water with
dissolved metal salt to enter the Bunsen burner.
8. Observe the color of the flame through the spectrometer. Record your
observations.
9. To clear out the metal salt, move the tiny diameter tubing into distilled
water and again pump air into the large tube.
Repeat the strategy with each of the known salt solutions.
CLEAN-UP and DISPOSAL
Turn off the Bunsen burner. Cap the bottles of salt solutions.
Siena College Green Chemistry Institute Lucas Tucker, Michale O’Brien, Ann Klotz Page 2 Student Name:___________________
Date: ___________________
TABLE 1: OBSERVATIONS
Viewing the flame through a spectroscope you can observe and record the
number of lines, the color of lines and whether the lines are narrow or broad.
Some spectroscopes also include a scale of wavelength.
Solution
Metal Color of flame
Water
None
Description of spectrum as viewed through
spectroscope.
CaCl2
CuCl2
LiCl2
NaCl
SrCl2
Lab Questions:
1.
The energy of visible light increases as follows: red, orange, yellow, green,
blue, violet. List the ions used in the flame test in increasing order of
increasing energy of emitted light.
2.
What color would you expect sodium nitrate to burn when introduced to a
flame?
3) Streetlights that glow with a slight yellow have sodium in them. Why do you
think that sodium was chosen rather than some of the others on this list?
4) In some country road where streetlights are infrequent they don’t use sodium
lights. Why might this be (hint: The advantage that you talked about above is
a disadvantage where there are less lights.)?
Siena College Green Chemistry Institute Lucas Tucker, Michale O’Brien, Ann Klotz Page 3 Green Question(s)
5) What is green about using a bike pump to provide the pressure to nebulize the
solutions?
Siena College Green Chemistry Institute Lucas Tucker, Michale O’Brien, Ann Klotz Page 4 TEACHER INFORMATION
Regents Core:
Atomic Concepts 1.10- When an electron returns from a higher energy state to a
lower energy state, a specific amount of energy is emitted. This emitted energy
can be used to identify and element (3.1k)
Teacher Tips:
Salts can be introduced into a flame in several different ways. Solid salt or a
solution of salt can be introduced into the flame of a Bunsen burner. Details of
this procedures are available on the American Chemical Society website.i
An alternative method is to introduce a mist of salt
solution into the air vent of the burner. This method
provides longer lasting flame color. Also, student’s
hands don’t need to be as close to the flame as they
are when using a wire or woodspint.
One way to do this is to put the mineral salt solutions
into a spray bottle and direct the spray at the air inlet
of a Bunsen burner. It is helpful to prevent overspray
by placing the burner inside a bottle. A T-shaped
opening is cut to allow the burner into the bottle. The
burner is positioned through the neck of the bottle.
Another opening is needed for the tubing for gas. A
third opening is needed for the spray bottle. This
third opening is located so that the spray is directed
near the burner inlet.
Figure 2: Spray Bottle Apparatus
Another way to introduce the salt solution into the
burner flame is to construct a nebulizer apparatus.
Materials:
Rubber stopper size 10
T-Type Connector size ¼ inch (Thermofisher product 6252-0250)
Microtubing, tygon, size 010 in ID x 030 inch OD and approximately 12 inches
long (Cole-Palmer product EW06419-00)
Tygon tubing ¼ inch ID
Tip for pipette that has opening to fit T-Type connector
Rigid tubing, plastic, approximately 5 inches long and ¼ inch OD
Epoxy glue
Put the t-connector in the end of the pipet tip. Thread the microtubing straight
across the t-connector and out the end of the pipet tip so that is it even or just
beyond the end of the pipet tip. Epoxy the microtubing into the end of the tconnector to form an airtight seal. Allow the epoxy to dry.
Siena College Green Chemistry Institute Lucas Tucker, Michale O’Brien, Ann Klotz Page 5 Cut two holes in the rubber stopper. Thread the 5-nch tubing through one of the
holes. Put the pipet tip in the second hole. Connect the ¼ inch ID tubing to the
other side of the T-connector.
Insert the stopper apparatus in a 250 mL Erlenmeyer flask. Secure the flask with
the attached apparatus to a support stand with a three-finger clamp. Position it
on its side so that the ridged tubing is at the air vent for the burner. Put the micro
tubing into the solution containing the metal ion. Connect the larger tubing to a
source of air. The source of air may be a bicycle hand pump , a small electronic
air pump or laboratory air. Light the burner and turn on the air. The gas
regulator valve may need to be adjusted when the air flow increases.
Sample Data
Solution Metal
Color of flame
Water
No metal
Blue
CaCl2
Calcium
Yellow-Orange
CuCl2
Copper
Green-Yellow
Green 540 nm, Sharp Yellow 590 nm, Red
610 nm
No lines visible
NaCl
Sodium
Yellow-Orange
Bright Sharp Yellow line at 590 nm
SrCl2
Strontium
Red
KCl
Potassium Light Violet
Green 500 nm, Yellow 590 nm, Orange
600 nm
No lines visible
Description of spectrum as viewed
through spectroscope.
No lines visible
Answers to Questions:
1. The energy of visible light increases as follows: red, orange, yellow, green,
blue, and violet. List the ions used in the flame test in increasing order of
increasing energy of emitted light.
Lowest Energy >(Ca2+ Sr2+), Na+, Cu2+, K+ >Highest Energy
2.
What color would you expect sodium nitrate to burn when introduced to a
flame? Yellow
3. Streetlights that glow with a slight yellow have sodium in them. Why do you
think that sodium was chosen rather than some of the others on this list?
Sodium emits a brighter light than the other metals.
Siena College Green Chemistry Institute Lucas Tucker, Michale O’Brien, Ann Klotz Page 6 4. In some country road where streetlights are infrequent they don’t use sodium
lights. Why might this be (hint: The advantage that you talked about above is
a disadvantage where there are less lights.)?
5. What is green about using a bike pump to provide the pressure to nebulize
the solutions?
When using a bike pump, the energy to move the air is supplied by the
individual using the pump and electricity is not used.
Energy is only expended when the pump is being used and not all the time.
Waste: Salt solutions may be stable for many years. When no longer
needed, then dispose of in a manner consistent with federal, state and local
regulations.
Solution
1 M CaCl2
1 M CuCl2
1 M NaCl
1 M SrCl2
1 M KCl
Environmental Disposal Method
Hazard
Low hazard
Consult your local water authority to determine if this
solution can be safely disposed into the sanitary sewer.
Moderate
Consult your local water authority to determine if this
toxicity
solution can be safely disposed into the sanitary sewer.
Low hazard
Consult your local water authority to determine if this
solution can be safely disposed into the sanitary sewer.
Low hazard
Consult your local water authority to determine if this
solution can be safely disposed into the sanitary sewer.
Low hazard
Consult your local water authority to determine if this
solution can be safely disposed into the sanitary sewer.
Which of the 12 principles of Green Chemistry were employed to make this
lab greener?
VPrevention It’s better to prevent waste than to treat or clean up waste
afterwards.
mAtom Economy Design synthetic methods to maximize the
incorporation of all materials used in the process into the final product.
mLess Hazardous Chemical Syntheses Design synthetic methods to use
and generate substances that minimize toxicity to human health and the
environment.
VDesigning Safer Chemicals Design chemical products to affect their
desired function while minimizing their toxicity.
mSafer Solvents and Auxiliaries Minimize the use of auxiliary
substances wherever possible make them innocuous when used.
mDesign for Energy Efficiency Minimize the energy requirements of
chemical processes and conduct synthetic methods at ambient
Siena College Green Chemistry Institute Lucas Tucker, Michale O’Brien, Ann Klotz Page 7 temperature and pressure if possible.
mUse of Renewable Feedstock’s Use renewable raw material or
feedstock rather whenever practicable.
mReduce Derivatives Minimize or avoid unnecessary derivatization if
possible, which requires additional reagents and generate waste.
mCatalysis Catalytic reagents are superior to stoichiometric reagents.
mDesign for Degradation Design chemical products so they break down
into innocuous products that do not persist in the environment.
mReal-time Analysis for Pollution Prevention Develop analytical
methodologies needed to allow for real-time, in-process monitoring and
control prior to the formation of hazardous substances.
VInherently Safer Chemistry for Accident Prevention Choose
substances and the form of a substance used in a chemical process to
minimize the potential for chemical accidents, including releases,
explosions, and fires.1
EPA: Twelve Principles of Green Chemistry. Retrieved from http://www.epa.gov/sciencematters/june
i American Chemical (2014) Safety Alert Rainbow experiment. Retrieved from Society.http://www.acs.org/content/acs/en/about/governance/committees/chemi
calsafety/safety-­‐alert-­‐rainbow-­‐demonstration.html?cq_ck=1392229885202. August 2014. Siena College Green Chemistry Institute Lucas Tucker, Michale O’Brien, Ann Klotz Page 8