From Warfare to Entertainment: The Chemistry of Fireworks By Emily Peterson, Ryan Stroud and Will Witwer

Introduction Since the first fireworks of ancient China, fireworks have been modernized significantly. The gunpowder present in the fireworks is no longer intended to frighten enemies, but is now used as a form of entertainment. Thus, compounds used to produce colors in fireworks have become commonplace over the years. Compounds that produce color in fireworks vary, though, depending on the preference of the maker and the ultimate height of the firework. However, different compounds will emit varying wavelengths of light. Inspired by the progress fireworks have made over the years, our goal was to find out what compounds were used in fireworks that we set off by simply observing the fireworks and comparing our observations to a color spectrum.

History The first fireworks in ancient China were made out of green bamboo that would be thrown into a fire to keep away evil spirits, Nian. The first accounts of gunpowder, though, is during the Sui and Tang dynasties (~ A.D.) when alchemists were experimenting with sulfurous mixtures in order to discover an elixir of life. The mixture of sulfur, saltpeter (potassium nitrate), honey, and arsenic disulfide was heated over a flame and resulted in a large explosion. The alchemists began experimenting with the mixture and resulted in huo yao, or the "fire chemical,” a crude form of gun powder. These explosions were used a form of entertainment initially but then made their way to warfare, used in the forms of fire arrows and noise bombs; the Chinese would use the explosives to frighten and confuse their enemies during battle. Eventually, this primitive form of gunpowder was advanced and was used in weapons such as cannons, guns, and grenades.

Equations Black powder, or gun powder, is commonly used as fuel in fireworks. Chemically, it is an age old mixture of nitrates, charcoal, and sulfur in a ratio of 75:15:10, respectively. Nitrates are the commonly used oxidizing agent, with potassium nitrate (KNO3) being the most commonly used. The below chemical equation represents what happens to the nitrate as it decomposes when a firework is lit: 2KNO3––>K2O + N2(g) + 2.5O2(g) As nitrates react like the one above, they release two of their three oxygen atoms. But because not all available oxygen is released, the reaction is less robust. Thus, the reactions of nitrates are more controlled than other oxidizing agents, and so they are safer and used as the major component of gunpowder. The combustion of gunpowder is quite complicated, but below is a commonly cited, simplified version: 2 KNO3 + S + 3 C → K2S + N2 + 3 CO2. The oxygen released by nitrates and other oxidizing agents combines with the reducing agents to produce hot, rapidly expanding gasses. Oxygen produces sulfur dioxide and carbon dioxide when reacting with the reducing agents, the most common of which are sulfur and carbon (charcoal): O2(g) + S(s)––>SO2(g) O2(g) + C(s)––>CO2(g)

Research Question How do varying chemicals alter the visual effects of fireworks? Hypothesis We predict that based on observation and research that we will be able to determine the color producing compounds present in each of the five different fireworks.

Experiment For our experiment, we wanted to find out how changing the color-producing chemicals in fireworks would effect the ultimate explosion. We decided that we would observe the fireworks at varying distances (20, 40, and 60 feet) and then guess the compound present within the firework by comparing our observations to a color spectrum. Ultimately, we researched the actual color-producing compounds present in the fireworks we set off and compared them to our guesses.

Materials Safety goggles Fire pit Fire extinguisher Safety matches Digital camera Digital camcorder Tripod Observation sheets Pens Adult supervisor Fireworks, 2 each: ‘Golden Glittering Flower’, ‘Green Glittering Flower’, ‘Tri- Color Sprayer’, ‘Happy Silvery Flower’, ‘Violet and Butterfly’ Measuring tape Place markers Water bucket

Process I.Research legality of fireworks by calling a local police department. II.Collect materials and travel to testing site. III.Set up testing area. Create a fire pit, measure distances and use place markers to show where 20, 40, and 60 feet from the fire pit are. Set up digital camcorder and digital camera. Place fire extinguisher at an accessible distance. Distribute observations sheets and pens. Determine firework order, and set fireworks that are not being lit off in an area a safe distance from the fire pit. IV.Press ‘Record’ on the digital camcorder, go to specified observation station, and station first firework in fire pit. Put on safety goggles. V.Have the person stationed at the first station (the 20 foot marker) light firework and travel back to post very quickly before explosion occurs. VI.Record observations during the explosion. VII.Wait for explosion to stop and smoke to disperse before approaching firework shell to safely remove it from the fire pit. Put firework shell in water bucket, and make sure it is totally submerged so as to douse the shell. VIII.Repeat steps 4-7 with each firework for two trials. IX.When finished with both trials, collect and dispose the doused firework shells safely. Turn off camcorder and camera. Collect all materials. Return all materials to their specified areas.

Light Table Color of Light ProducedCompound BurnedWave Length of Light Produced nm Redstrontium or lithium652 Orangecalcium668 Yellowsodium Greenbarium589 Bluecopper halides Purplepotassium or strontium + copper Goldiron and carbon Whitealuminum, titanium, or magnesiumVisible light

Predictions and Literature Values Chemical Compositions Firework NamePredicted Compounds Present in Fireworks Literature Values of Compounds Present in Fireworks Golden Glittering Flower Potassium Nitrate (KNO­ 3 ), Charcoal (C), Sulfur (S), Calcium (Ca), and Iron (Fe) Potassium Nitrate (KNO 3 ) moles Charcoal (C) moles, Sulfur (S) moles, Calcium (Ca) moles, Iron (Fe) moles Green Glittering Flower Potassium Nitrate (KNO­ 3 ), Charcoal (C), Sulfur (S), Calcium (Ca), and Barium (Ba) Potassium Nitrate (KNO 3 ) moles, Charcoal (C) moles, Sulfur (S) moles, Calcium (Ca) moles, Barium (Ba) moles Tri- Color Sprayer Potassium Nitrate (KNO­ 3 ), Charcoal (C), Sulfur (S), Calcium (Ca), Barium (Ba), Copper (Cu), and Lithium (Li) Potassium Nitrate (KNO­ 3 ) moles, Charcoal (C) moles, Sulfur (S) moles, Calcium (Ca) moles, Barium (Ba) moles, Copper (Cu) moles, Lithium (Li) moles Happy Silvery Flower Potassium Nitrate (KNO­ 3 ), Charcoal (C), Sulfur (S), Calcium (Ca), and Aluminum (Al) Potassium Nitrate (KNO­ 3 ) moles, Charcoal (C) moles, Sulfur (S) moles, Calcium (Ca) moles, Aluminum (Al) moles Violet and Butterfly Potassium Nitrate (KNO­ 3 ), Charcoal (C), Sulfur (S), Calcium (Ca), Copper (Cu), and Strontium (Sr) Potassium Nitrate (KNO­ 3 ) moles, Charcoal (C) moles, Sulfur (S) moles, Calcium (Ca) moles, Copper (Cu) moles, Strontium (Sr) moles

How predictions were made These predictions of what compounds were present in the fireworks were based upon the wavelengths of the colors we observed. Longer wavelengths tend to be more visible while shorter ones are harder to see. Thus, the predictions of what color producing chemicals are present in the fireworks are based upon our own observations as well as the wavelengths of the color producing compounds. For example, we predicted that the ‘Tri-Color Sprayer’ had lithium present within it instead of strontium because strontium produces a bright red color, which none of us saw.