Flame Test INTRODUCTION: By placing atoms of a metal into a flame, electrons can be induced to absorb energy and jump to an excited energy state, a quantum jump. They then return to their ground state by emitting a photon of light (the law of conservation of energy indicates that the photon emitted will contain the same amount of energy as that absorbed in the quantum jump). The amount of energy in the photon determines its color; red for the lowest energy visible light, increasing energy through the rainbow of orange yellow green blue indigo, and finally violet for the highest energy visible light. Photons outside the visible spectrum may also be emitted, but we cannot see them. The arrangement of electrons in an atom determines the sizes of the quantum jumps, and thus the energy and colors of the collection of photons emitted, known as an emission spectrum. In this way, the emission spectrum serves as a ‘fingerprint’ of the element to which the atoms belong. We can view the emission spectrum of colors all at once with the naked eye. It will appear to be one color, which we will carefully describe. A flame test is a procedure used to test quantitatively for the presence of certain metals in chemical compounds. When the compound to be studied is excited by heating it in a flame, the metal ions will begin to emit light. Based on the emission spectrum of the element, the compound will turn the flame a characteristic color. This technique of using certain chemical compounds to color flames is widely used in pyrotechnics to produce the range of colors see in a fireworks display. In this lab, we will record the flame test color of several metals by making solutions of salts, or ionic compounds, of those metals then igniting them with a match. We will observe the separate colors of the emission spectra, as the solution burns. If time permits, we will also compare the flame tests of crystals of a compound with that of a solution of the same compound. BACKGROUND: The electrons in an atom occupy different energy levels, as you know. When all of the electrons are at the lowest possible energy level, they are said to be in the ground state. Electrons do not always stay in the ground state. Sometimes they can be promoted to a higher-energy electron shell. This can happen in two ways. First, the electron can absorb a photon of just the right amount of energy to move it from one quantum shell to another. Second, when atoms are heated their electrons can gain energy from the heat. This promotes them to the higher-energy shell. When an electron is in a higher-energy shell it is said to be in an excited state. Electrons in excited states do not usually stay in them for very long. When electrons lose their energy, they do so by emitting a photon of light. Photons are particles with energy but no mass. Their energy is directly proportional to the frequency of the light (remember: E = hf; E is energy, h is Planck’s constant; f is frequency). The photons emitted precisely match the quantum energy difference between the excited state and the ground state. The spacing between the ground state and the higher energy levels is different for different elements. This gives rise to a way to uniquely identify elements based on their spectrum. A spectrum is the scientific name for a rainbow: light broken into the different wavelengths that make it up.
Flame Test PRE-LAB QUESTIONS Submit your answers to these questions (on a separate sheet of paper if more room is needed) before you begin the lab. What color of light is the lowest in energy? What color of light is the highest in energy? What color of light is the highest frequency? What color of light is the lowest frequency? How are electrons “excited”? What does it mean when the electrons are “excited”? In your own words, write a short explanation of how an electron absorbs energy and re-emits it as light and why different elements have different spectra.
1. red is the lowest light for energy.
2.violet is the highest light for energy
3. When an electron is in a higher energy state it is said to be in excited.
I think electrons absorb energy depending on how bright the color is. I think it might re emit it as a light because the colors can be so bright that it looks like a light.
Flame Test PRE-LAB QUESTIONS Submit your answers to these questions (on a separate sheet of paper if more room is needed) before you begin the lab. What color of light is the lowest in energy? What color of light is the highest in energy? What color of light is the highest frequency? What color of light is the lowest frequency? How are electrons “excited”? What does it mean when the electrons are “excited”? In your own words, write a short explanation of how an electron absorbs energy and re-emits it as light and why different elements have different spectra.
1. red is the lowest light for energy.
2.violet is the highest light for energy
3. When an electron is in a higher energy state it is said to be in excited.
I think electrons absorb energy depending on how bright the color is. I think it might re emit it as a light because the colors can be so bright that it looks like a light.