The below write-up is best designed for a high school-level chemistry class, not for elementary or middle school students, and it should be conducted by an experienced chemistry teacher. An alternative approach to this activity that can be conducted at the middle school level is to take a piece of nichrome wire and embed it in a wooden dowel. Prepare the same solutions as below except omit the methanol. Take the wire loop and heat it in a propane flame. Dip the wire loop in one of the metal salt solutions and then place the wet loop in the propane flame. The flame will take on a color characteristic of the element.
Science Discipline(s)
Chemistry
Topics
- Forms of energy
- Physical properties
- Light transmission
Activity Title
Colored Flames
Materials
- 5 liters Methanol
- 5 spray bottles (1/2 liter each)
- Bunsen burner
- 50 g lithium chloride
- 50 g copper sulfate
- 50 g sodium chloride
- 50 g potassium chloride
- 50 g magnesium sulfate
- 50 g Borax
- Protective gloves
- 5 Safety goggles
Procedure
- Use gloves when preparing the salt solutions!
- Take 25 g of lithium chloride salt and add it to a ½ L pray bottle then fill the spray bottle with methanol, put the spray lid on the bottle and shake to dissolve the lithium chloride salt.
- Repeat step 2 for all five salts. For the copper sulfate solution, add 25 g of Borax for green color.
- Distribute the spray bottles to a group of 5 students and have them put on safety goggles.
- Ignite the Bunsen burner.
- Allow each student to spray their salt solution into the flame of the Bunsen burner (make sure the students don’t get too close to the flame and make sure they only spray the flame!).
- Rotate each salt solution amongst the 5 students so each of them get a chance to spray the 5 different salt solutions.
Questions
- Which variables are important in this activity? How could you design an experiment to test whether the variables are important?
- What kind of energy does the flame provide?
- What process takes place when metal salts emit light?
- Would you expect metal salts different from the metal salts we used to have the same flame colors? Why or why not?
Explanation
All atoms have electrons traveling around their nucleus in what is called orbitals. These orbitals are areas around an atom in which the electrons have the highest probability of being found. There are many different orbitals found within an atom and each orbital has its own specific energy level associated with it. Provided enough energy, electrons can go up in energy levels. However, electrons prefer to be in lower energy levels and as a result, they fall back down to their lower energy levels. When this process happens, electrons emit electromagnetic radiation (light) with energy that is proportional to the difference in energy levels that the electron has traveled. Furthermore, each element has its own unique ground state energy level which means that every element emits its own unique spectra of light when its electrons undergo a transition in energy levels.
Next Generation Science Standards
This activity could be implemented at the middle school grade level as a simple and fun science experiment. Kids will learn about different forms of energy, characteristic properties of elements and light transmission. A demonstration of how electrons emit light can be done by drawing the Bohr model of an atom and explaining how electrons jump from one orbit to another and that when they undergo this jump, electrons either absorb or emit light.
Areas of the NGSS that this activity links to are: 1-PS4-2 Objects can be seen if light is available to illuminate them or if they give off their own light. 2-PS1-4 Heating or cooling a substance may cause changes that can be observed, 4-PS3-2 & 4-PS3-3 Energy can be moved from place to place by moving objects or through sound, light, or electric currents. 4-PS3-2 & 4-PS3-3 Energy is present whenever there are moving objects, sound, light, or heat. 4-PS3-2 Light also transfers energy from place to place. 5-PS1-3 Measurements of a variety of properties can be used to identify materials. MS-PS3–5 Energy may take different forms (e.g., energy in fields, thermal energy, energy of motion), MS-PS1-3 Each pure substance has characteristic physical and chemical properties that can be used to identify it. MS-PS1-4 The term “heat” as used in everyday language refers both to thermal energy (the motion of atoms or molecules within a substance) and the transfer of that thermal energy from one object to another. MS-PS4-2 When light shines on an object, it is reflected, absorbed, or transmitted through the object, depending on the object’s material and the frequency (color) of the light.
