Fireworks are a spectacular demonstration of chemistry in action.
Early fireworks, invented by the Chinese in the 9th century were largely associated with golden sparks, flashes and bangs. Over the next 12 centuries advances in chemistry have made fireworks more colourful giving us brighter displays on a larger scale but behind every display is some real science.
How do fireworks produce their colours?
The colours in fireworks are produced by certain chemical compounds containing metal ions. When these compounds are heated to high temperatures, energy excites electrons within the atoms. As the electrons return to lower energy levels, they release energy as light. Different elements have different arrangements of electrons and energy levels. So, they emit light at particular wavelengths, which we see as distinct colours.
This is known as atomic emission and is the principle behind flame tests and atomic emission spectroscopy.
The colours
Different metal ion compounds can produce characteristic firework colours:
| Colour | Metal commonly responsible | Typical flame-test colour |
| Red | Lithium | Crimson red |
Yellow | Sodium | Intense yellow |
| Lilac | Potassium | Pale violet |
| Orange | Calcium | Brick red or orange-red |
| Green | Barium | Pale green |
| Blue-green | Copper | Blue-green or emerald green |
Flame-test practical
A flame test is a simple way to investigate the relationship between chemical composition and colour. It gives you the chance to see, record and compare results while connecting practical observations to atomic structure.
Equipment
Samples need to be small amounts of the salt chlorides solutions, following the school's risk assessments and relevant safety data sheets.
Method
- Put on safety glasses, tie back long hair and set up the bunsen burner on a heat-resistant mat.
- Use separate, wooden splints soaked in distilled water and then in the chosen salt solutions labelled appropriately.
- Hold the treated end of a splint at the edge of the burner flame. It would be advisable to carry out the sodium chloride solution last
- Observe the flame colour and record it in a results table.
- Extinguish and dispose of each used splint in a beaker of water. Never reuse a contaminated splint for another sample.
Safety first: This experiment involves an open flame and chemical solutions. It must be supervised, with safety eyewear and normal laboratory safety procedures in place. Barium salts require particular care because of their toxicity, if used. Chemical residues should be disposed as per CLEAPSS advice
Record your observations.
Make a table of your colours and use it to identify an unknown solution based on your observations.
From the Bunsen burner to atomic spectroscopy
The flame test is more than a colourful practical. It leads to a complex analytical technique used by chemists to identify elements.
When emitted light is examined using a spectroscope, it can be separated into characteristic wavelengths. The resulting emission spectrum acts like a chemical fingerprint. More advanced instruments can use these wavelengths to identify elements and, under suitable conditions, measure their concentrations.
Make the most of this Bonfire Night this year with SLS Select Education
Explore these laboratory essentials to support flame-test practicals and help students investigate the science behind the colours.
Explore the products and bring the science behind every spark into your classroom. Ensure all practicals follow your school's risk assessments and relevant safety guidance.