Firework colours: flame tests and spectral lines
About this app
Fireworks in the night sky for Guy Fawkes Night: every colour comes from one element in the star mix — strontium red (SrCl, SrOH), barium green (BaCl), copper blue (CuCl), sodium, lithium, calcium, potassium, magnesium white. A spectroscope shows lines and bands, an energy diagram the photon with E = h · c / λ. Why blue is so hard (CuCl breaks down in hot flames), plus a puzzle: identify the unknown rocket from its spectrum.
With explain mode: an AI tutor walks you through the app, points out what matters in the scene and answers your questions.
What it is about
The colours of fireworks come from the star compositions, mixtures containing metal salts. The flame excites atoms or small molecules. When an electron drops back to a lower energy level, it emits a photon with exactly the energy difference, E = h · f = h · c / λ. Atoms such as sodium or lithium give sharp spectral lines, molecules such as SrCl, BaCl or CuCl broader bands, because each electronic state comes with many vibrational levels. Glowing particles of magnesium or aluminium oxide, by contrast, emit a continuous spectrum and look white.
What the app shows
Rockets rise above a city at night and burst into stars. Eight star compositions are available: strontium, lithium, calcium, sodium, barium, copper, potassium, and magnesium with aluminium. A spectroscope panel shows the line or band spectrum next to the spectrum of white light, with the emitter and signature wavelengths. An energy diagram lifts the electron and lets it drop back, stating wavelength, frequency and photon energy. For copper, a temperature slider shows how CuCl breaks down above about 1200 °C.
Try it yourself
Launch strontium and then lithium. Both glow red, yet their spectra are easy to tell apart. Make the flame hotter for copper and watch the blue fade. In the puzzle a rocket without a label goes up: identify the element from its spectrum; a wrong answer shows the comparison spectrum. For Guy Fawkes Night on 5 November there is also a grand finale with five colours.
Frequently asked questions
- Which elements give fireworks their colours?
- Red comes from strontium, green from barium, blue from copper. Sodium colours yellow-orange, calcium orange and lithium crimson. Magnesium and aluminium provide white sparkle. Violet is usually mixed from strontium and copper.
- Why are blue fireworks so hard to make?
- The blue comes from the molecule CuCl. It breaks down in flames that are too hot, above about 1200 °C, and the blue fades. Blue star compositions therefore have to burn cooler and supply enough chlorine.
- What is the difference between a line and a band spectrum?
- Free atoms emit light at a few sharply defined wavelengths, sodium for example at 589 nm. Molecules also have vibrational levels. Their many closely spaced lines merge into bands in the spectroscope.
- What can I adjust in the app?
- You choose one of eight star compositions and launch rockets, set the flame temperature for copper, switch the automatic fireworks on or off, view the spectrum and energy diagram, and solve puzzles from the spectrum.
Subject: Chemistry
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