Flame Test Fireworks How Are the Fireworks Colors Made? Have you ever wondered h
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Flame Test Fireworks How Are the Fireworks Colors Made?
Have you ever wondered how the beautiful colors of the fireworks are generated? Fireworks come in an array of colors from yellows and reds to blues and greens (Figure 1). The colors are produced by heating metal salts. For example, sodium chloride (NaCl) burns yellow, and calcium chloride (CaCl2) burns orange.
Electron States and Color
Many elements and crystalline salts have a distinct color when burned over a flame. This color can be used to identify a chemical compound. The distinct color produced by each element is the result of the different valence electrons in their specific orbitals.
The ground state of an element is a specific electron arrangement that is the most energetically favorable. When an element is heated, the valence electrons absorb the energy from the heat, or become excited, and move to a higher-energy orbital. Given that higher-energy orbitals are not stable, the excited electron quickly returns to the ground state.
For example, sodium ion has a 1s22s22p6 ground state electron configuration. When heated, the electrons gain energy and can be excited into a higher-energy level such as 4s as shown in Figure 2. Because this excited state is unstable, the excited electron will drop back down to the ground state level and emit energy as light.
Figure 2. Sodium Ion Electron Configuration and Flame Color
Electrons move from the ground state to an excited state when heated.
Depending on the amount of energy provided, more than one electron can be excited, and therefore more than one wavelength of light will be emitted. In addition, the electron may not return all the way to the ground state, so various wavelengths are possible from the same excited electron. The combination of the wavelengths emitted by an element gives the flame its color.
The energy the valence electron absorbed when it was excited is re-emitted as a photon of light. That photon has the precise amount of energy needed to move that valence electron and thus has a particular wavelength. Therefore, the particular color emitted by an element or compound when it burns is caused by the particular wavelength of light emitted when its valence electron moves from an excited state to ground state. Examples of colors emitted by substances are listed in Figure 3.
Metal
Flame Color
lithium
red
strontium
scarlet
calcium
orange-red
magnesium
bright white
zinc
light green
copper
blue-green to green
barium
apple green
phosphate
blue-green
manganese
yellow-green
lead
blue
bismuth
azure
arsenic
blue
potassium
violet
Figure 3. Flame Color of Selected Substances
Limitations of the Flame Test
Although the combinations of wavelengths of light emitted by each element are different, the colors produced may be similar enough that the naked eye may not be able to distinguish them. Contaminants may also alter the color of the flame. For example, sodium is present in most compounds and will color the flame. A blue glass can filter out the yellow from sodium if necessary. Another limitation of the flame test is that it cannot detect very low concentrations of ions.
About This Lab
In this lab, you will test a range of elements and compounds to observe the range of colors emitted by them when inserted into a flame. You will compare the colors you observe to the expected results provided in the background.
Take a Bunsen burner from the Instruments shelf and place it onto the workbench.
Turn the Bunsen burner to the low flame by clicking the knob at the bottom once.
Take the first culture tube from the Materials shelf and place it onto the workbench.
Note: Unlike most materials in our labs, the materials in this experiment can be placed directly on the workbench rather than adding them to a container.
Take a clean wire rod from the Instruments shelf and place it into the culture tube. You should observe the wire rod dipping into the culture tube.
Flame the wire rod by moving it onto the Bunsen burner.
Observe the color of the flame as the chemical compound is burned. Record the name of the material and the results in your Lab Notes.
Discard the culture tube and wire rod by dragging them to the recycling bin underneath the workbench.
Repeat steps 3 – 7 for each material on the Materials shelf. Remember to press Save Notes.
Lab Notes:
Bismuth =Blue
Lithium Nitrate = pink-purple Reddish
Strontium Nitrate = pink reddish
Calcium sulfate = pink reddish
Magnesium = white
Magnesium Nitrate = very light blue
Zinc = light blue
Coper (II) chloride = dark blue-green
Barium chloride = light green
Barium sulfate = greenish yellow
Magnesium sulfate = greenish yellow
Lead nitrate = med blue
Arsenic acid = blue-purple
Potassium iodide = violet-purple
Answer the following 4-part question:
Question 10
a. What is the ground state of an element?
A. It is the arrangement of electrons that occurs at room temperature or below.
B. It is the most energetically favorable arrangement of the element’s protons.
C. It is the most energetically favorable arrangement of the element’s electrons.
D. it is the arrangement of electrons that occurs after one or more electrons becomes excited.
b. Why do certain elements produce color when heated in a flame?
A. Electrons absorb energy from the flame and become excited, which causes them to emit light.
B. Electrons absorb energy from the flame and become excited. Upon returning to the ground state, they emit light.
C. Electrons absorb energy from the flame and turn into photons of light.
D. Electrons are in a constant state of excitation that causes them to emit light.
c. Which of the following statements is true?
A. Only one electron can be excited at a time.
B. Excited electrons do not return to ground state until they move away from the heat of the flame.
C. An electron may fall back to ground state in a single step or in multiple steps.
D. Each element emits a single, characteristic wavelength of light during the flame test.
d. A flame test could be used to distinguish which of the following two substances?
A. lithium nitrate and strontium nitrate
B. arsenic acid and lead nitrate
C. copper (II) chloride and calcium sulfate
D. bismuth and lead nitrate
Metal
Flame Color
lithium
red
strontium
scarlet
calcium
orange-red
magnesium
bright white
zinc
light green
copper
blue-green to green
barium
apple green
phosphate
blue-green
manganese
yellow-green
lead
blue
bismuth
azure
arsenic
blue
potassium
violet
Explanation / Answer
Ans. 10. Correct option: C. it is the most favorable arrangement of element’s electrons.
The native electronic configuration of an element in its elemental state is called its ground state. It is the most stable, thus, most favorable arrangement of the electrons in atomic orbitals.
The ground state of an element may be stable under various range of temperature and the conditions present around the element. For example, a piece of metal placed in dilute HCl at 100C reacts with HCl and it’s ground state configuration is changed. Thus, in this case, ground state is not dependent on temperature.
Ans. 11. B.
Heat energy (flame) is also a form of electromagnetic radiation.
Electrons absorb EMR and reach a higher energy level, called the excited state. The excited electron releases EMR while is returns backs to ground state.
For an EMR, Energy, E= hv , where, v= frequency of EMR
Also, speed of an EMR = v l , where, l = lambda = wavelength
If the radiation emitted by the excited electron while coming back to ground state has the wavelength in visible range (400-700 nm), the color change is noted depending on the wavelength.
Ans. 12. C. The excited electron returns to ground state in a single step or multiple steps.
About option D: Incorrect. Two or more elements can give similar/ identical flame test results undistinguishable by naked eye.
Ans 13. Correct option C.
A. Lithium nitrate (dark red) ; strontium nitrate (red) = difficult to distinguish
B. difficult to distinguish
c. Well -differentiated color
D. difficult to distinguish
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