In this lesson, we’ll be learning how to use the flame test to identify different metal ions. By the end, you’ll be able to explain how to do the test and predict which metals will produce which color flames.
What Is a Flame Test?
Picture a New Year’s Eve celebration. You can’t wait to see the fabulous fireworks display. As you all count down to the New Year, bursts of light dazzle the sky. Bright reds, oranges, blues, and greens explode, leaving a light haze in the air.
Have you ever thought about what makes those brilliant colors? Surprisingly, all that fun comes down to chemistry. Inside fireworks are different metals, and when they are ignited they give off different colored light.
Chemists use this same principle to determine the identity of unknown metals using a flame test. During a flame test, chemists take an unknown metal and put it under a flame. The flame will turn different colors based on which metal is in the substance. The scientists can then identify their unknown substance. Let’s take a detailed look at how this works.
How Does the Flame Test Work?
Metals are composed of individual atoms, which contain a nucleus of protons and neutrons and outer shells of electrons, which float freely around the nucleus. Metal atoms usually exist as ions, or an atom with a charge. Metal ions are usually cations, meaning they carry a positive charge.
The electrons of metal ions circle the nucleus in layers called orbitals. As the orbitals get farther away from the nucleus, their energy level increases. Electrons need to absorb energy to move to a higher energy orbital.
As it turns out, this is exactly what happens during the flame test. During the flame test, metal ions are exposed to thermal energy, or heat, from the flame. The electrons in the outer orbital absorb the energy and temporarily bounce to a higher energy level. However, the electrons don’t stay put there. Eventually, they fall back to their original, ground energy level. As they fall back to the lower energy level, they release the energy they absorbed as light.
Light can be all different colors, depending on a property of light waves, called wavelength. Wavelength is the distance between peaks on the light waves. Light with longer wavelengths appears red, and light with shorter wavelengths appears purple.
Metals all have different configurations of electrons, which will produce different wavelengths of light during the flame test. The different wavelengths are seen as different colors. Thus, each particular metal will give off a characteristic color of light, which makes the flame change colors. Lithium is a metal that produces light with a longer wavelength during the flame test, which makes the flame turn red. Substances containing sodium turn orange, while substances containing calcium turn more of a yellow-red color. Substances with potassium ions produce a light purple flame and copper produces a characteristic blue-green color.
|Metal Ion||Flame Test Color|
How Do You Use the Flame Test?
So now that you’re excited about the flame test, let’s learn how to use it safely. Like any experiment involving chemicals and heat, you’ll need to take all the safety precautions. Use heat resistant gloves, goggles, and a chemistry apron to protect yourself. Be extremely careful when using the flame and always move anything flammable away from your workspace. If you have long hair, be sure to tie it back so it doesn’t swing into the flame.
First, make sure your flame test loop is totally clean. If it has any residue on it, it could affect the color of the flame and your results. If your loop needs to be washed first, you can dip it in acid and then rinse with water and dry.
Next, light your bunsen burner after carefully connecting it to the gas. Make sure the flame isn’t too low, but not so high that it’s blowing in the air. Dip your clean loop into your substance and bring the loop to the edge of the flame. Pass it through the flame and observe the color change. You can then look at a table of known color changes to decide which metal is contained in your substance.
Metal ions are positively charged atoms that give off a characteristic color during the flame test. When thermal energy is absorbed by the electrons in the metal ion, they jump to a higher orbital. When they fall back to their ground level orbital, they release energy as light. Each metal ion has a unique configuration of electrons, so each metal releases light of a different wavelength, which corresponds to a different color.
|Metal Ion||Flame Test Color|
To perform the flame test, dip a clean loop into the substance and pass it through a flame, observing the color. Then compare the color to the known emissions of different metal ions.