Have you ever watched a firework show and wondered how all the different colors—amazing reds, yellows, reds, blues, purples, greens and more—are made? The color, or colors, that a firework makes depends on what color-producing chemicals are in it. These chemicals are various metals that burn when the firework goes off, and it's the burning metals that create the vivid colors. Different metals give off different, specific colors. In this science activity you will get to burn some metals at home to investigate what colors they make. Then at the next fireworks show you can impress friends and family with your knowledge of what may be causing some of the colors they see!
Astronomers can figure out what distant stars are made of (in other words, their atomic composition) by seeing what type of light the star produces. In this activity you will do something similar by observing the color of flames when various chemicals are burned. How does it work exactly? It comes down to atoms and energy.
All matter is made of atoms. Atoms have a nucleus that is surrounded by electrons. Electrons moving around the nucleus have certain amounts of energy, called energy levels. If electrons gain energy, they move from their energy level to a higher one through distinct steps. Likewise, if electrons lose energy, they drop to a lower energy level. The lost energy can be carried away in the form of heat or as light (a photon). Exactly how much energy is lost affects what kind of light is made, which we may perceive as a difference in its color.
- Adult helper
- Table salt (chemical name: sodium chloride)
- Small plastic bag
- Six bamboo skewers
- White glue
- Copper sulfate (This is available via pet or aquarium stores and is used to combat algae or it is sold by home improvement stores as a root killer. Make sure the product is pure copper sulfate and that it is in the form of powder or small crystals.)
- Matches or lighter
- Candle (Choose one that can either stand on its own or has a sturdy stand.)
- Outdoor surface (A place where you can safely burn a candle after it becomes twilight or dark outside. Be sure it is in an open area to allow good airflow.)
- Container of water
- Disposable gloves (These are strongly recommended for handling the copper sulfate.)
- Safety goggles (recommended)
- Flashlight (optional)
- Pour a small amount of table salt (roughly one tablespoon) into a small plastic bag.
- Apply a thin layer of glue to the top one inch of the tip of a skewer. Just a little bit of glue is enough.
- Dip the glue-coated tip of the skewer into the salt in the bag. Twist the skewer back and forth a bit to coat the skewer's tip with the salt. Set the skewer aside to dry. Repeat this with two more skewers so you have a total of three skewers that have their tips coated with salt.
- Next, have an adult coat three more skewers with copper sulfate. Read and follow all safety precautions on the packaging that the copper sulfate came in. Be careful not to let anybody inhale any copper sulfate dust or get any on their skin or face. If desired, use disposable gloves and safety goggles. If not using gloves, be sure not to touch the copper sulfate. Coat the last inch of the tip of a skewer in a thin layer of glue and dip the glue-coated tip into the bag of blue-colored copper sulfate, twisting it back and forth to coat the tip. Repeat this with two more skewers so that you have three with coated tips.
- Allow all six of your skewers to dry. This may take about half an hour.
- When you later burn the skewers, be sure to do it in an open, outdoor area and be careful not to breathe the fumes or smoke from the skewers coated in copper sulfate.
- Adult supervision is required when using fire, burning the skewers and handling the copper sulfate.
- When it is dark (or twilight), take your candle, matches and prepared skewers to an open area outside where you can safely burn a candle. Be sure there is good airflow and always stand upwind of the flame (so that the breeze carries the smoke away from you). Also have a container of water with you as a safety precaution.
- Have an adult light the candle.
- Once the candle is burning well and you are on the upwind side of the flame, carefully take out one of the prepared skewers and hold the chemical-coated end in the flame. Be sure not to breathe the fumes or smoke from the burning skewer! What color does the chemical burn? How does it compare with the normal color of the candle's flame? You may be able to see the color in the candle's flame or by holding the skewer away from the candle (once the chemicals have caught fire) and looking at the flame on the tip of the skewer.
- The skewer may also catch fire after a few moments. If this happens, remove it from the flame and extinguish it in the container of water.
- Repeat this process for the other five skewers. (To help you distinguish which chemical you are burning, remember that the skewers coated in sodium chloride (table salt) will have white-coated tips and those coated in copper sulfate will have blue-coated ones.) Which color does the sodium chloride burn? Which color does the copper sulfate burn?
- Extra: You could try this activity using other metals known to produce certain flame colors when burned. Check out the "More to explore" section for details on doing this. Be sure to always look into and follow all proper safety precautions when handling different chemicals and burning them. What colors do other metals make when burned?
Observations and results
Did the sodium chloride–coated tip burn pure yellow-orange and the copper sulfate burn bluish-green?
A typical flame will burn yellow-orange with a little bit of blue near the base of the wick. When you burned the skewer tip coated with sodium chloride, you should have seen that the flame was pure yellow-orange (without any blue). This is because when the metal sodium is burned, it makes intense yellow-orange light. When you burned the skewer tip coated with copper sulfate, you should have seen that the flame gained blue-green traces. This is because when the metal copper is burned, it makes bluish-green light.
If an atom's electrons lose energy, they drop down to a lower energy level, and the lost energy can be released as light. Different types of atoms, or elements, have different gaps between their energy levels, which causes them to make light of different colors when they're burned and lose that energy.
Be sure to extinguish the candle and the skewers when you are done with the activity. When you are sure they have been extinguished (after dipping them in the water container), you can dispose of the used skewers in the garbage.
More to explore
Flame Tests, from University of California, Davis, ChemWiki
Flame Tests: Flame Coloration by Element, from Mineral News
Fun, Science Activities for You and Your Family, from Science Buddies
Rainbow Fire, from Science Buddies
This activity brought to you in partnership with Science Buddies