What is the science behind fireworks? How do they appear in different colors? Our Class 10 scholars have the answer — and they can replicate the process themselves.
Spread across three lab tables in Room 805 were 250 mL beakers, laboratory burners, weighing dishes and wooden splints soaked in distilled water. Surrounding each lab table were Class 10 students, eagerly prepping their materials and securing their safety goggles.
As part of their electrons unit, these Upper School chemists were commencing a hands-on investigation to determine the color emitted by different metal salts when heated in a flame.
Among their laboratory supplies were the six metal salts they would be testing: calcium, copper, lithium, potassium, sodium and strontium. The students began by filling one beaker halfway with distilled or deionized water and another with tap water for extinguishing.
After the students labeled their weighing dishes, placed a small scoop of each metallic salt into the appropriate dish, they were ready to begin their tests.
The students took turns dipping the damp end of the wooden splints into a specific metal and carefully placing it into the flame. Each lab group watched in awe as the flame flickered in hues of bright green, vibrant blue, deep orange or pinkish/red. After recording their observation, they placed the burning wood into the rinse water.
When a metal ion is heated, its electrons can absorb energy and move to excited energy levels, the students learned. As they return to lower levels, the electrons release energy in the form of light, called a photon. The energy of each emitted photon determines the color observed in the flame. As different metals have different electron arrangements, each produces its own flame color.
During their class discussions, the scientists also learned about the electromagnetic spectrum, of which the visible portion is quite small. Light of 400 nm appears violet while light of 700 nm appears red. According to the equation provided in their lab, wavelength is inversely proportional to energy and the colors observed include red, orange, yellow, green, blue, indigo and violet. As the color of light changes, so does the amount of energy.
In their lab, the students were provided with a table that listed each color’s representative wavelength in nanometers. Once finished with the flame tests, the students grabbed their calculators and pencils to complete the mathematical component on the following pages.
The students were required to convert each of the wavelengths from the given data table from nanometers to meters. They were also tasked with calculating the change in energy for each metal and predicting what the color of the flame would be if they heated cupric nitrate, sodium sulfate and potassium nitrate.
Throughout this active lesson, our scientists’ enthusiasm and confidence was on full display!
