Name: flame test metal color clues
Uploaded: 2020-03-26T07:22:25.000Z
Duration: 2 min 47 s
Channel: JoVE

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IPC.7.E

Metal Flame Emission

La prueba de llama es una técnica analítica en la que se aplica una muestra a una llama y se utiliza el espectro de emisión característico para identificar diferentes elementos. Cuando esta técnica se utiliza para identificar especies metálicas, se denomina prueba de emisión de llamas metálicas. Cuando se aplica suficiente energía a algunos metales a través de una llama caliente, emiten luz con una longitud de onda o color característico. Se puede ver claramente este fenómeno cuando se observa un espectáculo de fuegos artificiales.
Diferentes metales emiten diferentes colores. Por lo tanto, podemos usar el color de la luz emitida para determinar el metal presente. Pero antes de profundizar en la técnica, demos un paso atrás. Los átomos tienen múltiples niveles de energía para sus electrones, que son diferentes para cada elemento.
Cuando un electrón está en su nivel de energía más bajo posible, se dice que está en su estado fundamental. Cuando un átomo absorbe energía, se excita y los electrones del átomo pasan del estado fundamental a un nivel de energía más alto. Cuando los electrones se relajan a un estado más bajo, o al estado fundamental, el exceso de energía obtenida se libera en forma de luz emitida.
La longitud de onda de la luz emitida depende del nivel de energía al que se excitó el electrón y del nivel al que se relaja. Esta longitud de onda emitida, o color de luz, es específica del átomo presente y se utiliza para identificar una muestra de metal en la prueba de emisión de llama metálica.
En la prueba de emisión de llama metálica, aplicamos una muestra de metal a una llama caliente y observamos el color de la luz emitida. Por ejemplo, el bario emitirá un color verde amarillento en la llama, mientras que el cobre emite un azul verdoso y el potasio un púrpura rosado.
Ahora, una muestra en realidad consiste en el metal, iones metálicos, óxidos metálicos, hidróxidos metálicos y sales metálicas. Y dado que los átomos y las moléculas absorben y liberan energía de manera diferente, la luz emitida en realidad contiene un rango de longitudes de onda e intensidades que forman un espectro de emisión.
Un espectrofotómetro se utiliza para medir el rango de longitudes de onda de la luz emitida. 
En este laboratorio, utilizará la prueba de emisión de llama metálica para identificar varios metales y luego analizará la luz emitida y absorbida con un espectrofotómetro.

emisión de llamas metálicas

<h4>Emisión de llamas metálicas</h4>
La prueba de llama es una técnica analítica en la que se coloca una muestra en una llama y se utiliza el color característico de la llama para identificar la sustancia. Cada elemento tiene una emisión de luz característica cuando se coloca en una llama, lo que significa que cada elemento produce un color único. Este fenómeno se utiliza en espectáculos de fuegos artificiales, donde el color de los fuegos artificiales corresponde a una característica específica de un metal. La emisión de luz coloreada de una muestra en combustión es el resultado directo de que el componente metálico absorba energía debido a la excitación de la llama y emita luz como resultado.
<h4>Emoción de electrones</h4>
Cuando una especie atómica o molecular absorbe energía, la energía se utiliza de cuatro maneras diferentes. En primer lugar, la energía se utiliza en la traducción, lo que hace que las moléculas se muevan más rápido. En segundo lugar, la energía se utiliza en vibración, lo que hace que la distancia entre las especies cambie rápidamente. En tercer lugar, la energía provoca la rotación, que induce la rotación de los átomos alrededor de los enlaces de la molécula. Finalmente, la energía absorbida da como resultado la excitación de electrones, lo que hace que los electrones se muevan a un nivel de energía más alto desde el estado más estable o fundamental.
Según el modelo de Bohr del hidrógeno, los electrones de un átomo existen en estados discretos, que corresponden a capas individuales u orbitales alrededor del núcleo. El estado de energía más bajo se denomina estado fundamental y se representa mediante la notación de n = 1. Los estados de energía excitados tienen energías más altas y se representan mediante la notación de n = 2, 3, 4, etc.
Para que los electrones se muevan a un estado de energía más alto, deben absorber una cantidad de energía que sea igual a la diferencia entre su estado fundamental y el estado de energía más alto. Por ejemplo, si un electrón absorbe una cantidad de energía que es igual a la diferencia entre el estado fundamental y el nivel de energía n = 3, el electrón se moverá al nivel de energía n = 3. Un electrón puede relajarse espontáneamente hasta el estado fundamental o cualquier otro nivel de energía más bajo. Cuando esto ocurre, se emite un fotón que libera la energía absorbida.
La energía liberada se emite en forma de luz. La luz emitida tiene una energía característica, y por lo tanto, una longitud de onda, que se correlaciona con los niveles de energía del átomo. La luz visible, que es la luz que los humanos pueden ver con sus ojos, oscila entre unos 400 nm y 700 nm en el espectro electromagnético.
Las absorciones y emisiones atómicas son longitudes de onda discretas, llamadas líneas. Estas líneas son características únicas de un elemento, como un código de barras, y se pueden usar para identificar el elemento.
<h4>Prueba de emisión de llama metálica</h4>
En la prueba de emisión de llama metálica, se coloca una muestra de metal en una llama. La llama proporciona la energía para excitar electrones a un nivel de energía más alto. A medida que los electrones se relajan hasta el estado fundamental, la luz se emite con una energía específica en relación con los niveles de energía de los átomos en la muestra. Dado que los diferentes átomos tienen diferentes niveles de energía, la energía absorbida y emitida por una muestra, y por lo tanto la longitud de onda, es específica de la muestra.
Los metales tienen longitudes de onda de emisión atómica características en el rango visible que se determinan fácilmente mediante inspección visual. Por ejemplo, el litio emite un color rojo, el sodio emite un color amarillo, el potasio emite un color rosa-púrpura y el bario emite un color amarillo-verde.
Si bien las emisiones atómicas son longitudes de onda o líneas discretas, la mayoría de las muestras de metales contienen no solo el metal, sino también varios iones metálicos, óxidos y sales. Dado que cada átomo absorbe y emite una longitud de onda característica de la luz, la luz absorbida y emitida de la prueba de llama contiene un rango de longitudes de onda. Por lo tanto, los espectros de absorción y emisión atómica se pueden medir para la muestra utilizando un espectrofotómetro.
Las longitudes de onda y las formas de los espectros son únicas para cada sustancia. Por ejemplo, la intensidad relativa de las características del espectro depende de la concentración de las especies. Las intensidades absolutas dependen de la distancia de la muestra al espectrofotómetro.
<h4>Referencias</h4>
<ol>
	<li style="font-size:17px">Kotz, J.C., Treichel Jr, P.M., Townsend, J.R. (2012). Química y reactividad química. Belmont, CA: Brooks/Cole, Cengage Learning.</li>
	<li style="font-size:17px">Silderberg, M.S. (2009). Química: La naturaleza molecular de la materia y el cambio. Boston, MA: McGraw Hill.</li>
	<li style="font-size:17px">Harris, D.C. (2015). Análisis químico cuantitativo. Nueva York, NY: W.H. Freeman and Company.</li>
</ol>

Emisión de llamas metálicas

Emisión de llamas metálicas
La prueba de llama es una técnica analítica en la que se coloca una muestra en una llama y se utiliza el color característico de la llama para identificar ...

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flame test metal color clues

Flame testing uses a metal sample and a flame to identify a substance by its color. Each element gives off a characteristic light emission in the flame, so the color can help distinguish one element from another. This same idea appears in fireworks, where different metal components create different colors.

The color comes from energy absorbed by the metallic component. When a species absorbs energy, that energy can go into translation, vibration, rotation, or electron excitement. Electron excitement is the key step in flame emission because it moves electrons from the ground state, the lowest energy state, to a higher energy level.

In the Bohr model of hydrogen, these energy states are separate, or discrete. The ground state is written as n = 1, and higher states are written as n = 2, 3, 4, and so on. An electron moves up only if it absorbs the exact energy difference between its current level and the higher one.

The electron can then relax back to the ground state or another lower level. When that happens, a photon is released as light. The emitted light has a specific energy and wavelength, and visible light ranges from about 400 nm to 700 nm. These atomic absorption and emission wavelengths are discrete lines, and they act like a barcode for identifying an element.

In a metal flame emission test, the flame supplies the energy that excites the electrons. As the electrons fall back down, the sample gives off light with a wavelength tied to its atomic energy levels. Because different atoms have different energy levels, the emitted wavelength is specific to the sample.

Many metals show visible colors that are easy to spot by eye. Lithium gives a red color, sodium gives yellow, potassium gives pink-purple, and barium gives yellow-green. Real samples often contain metal ions, oxides, and salts as well as the metal itself, so the light from the flame test can include a range of wavelengths.

That range can also be measured with a spectrophotometer as atomic absorption and emission spectra. The shapes and wavelengths of the spectra are unique for each substance. The relative intensity of spectral features depends on concentration, while the absolute intensity depends on the distance from the sample to the spectrophotometer.

Flame Test Metal Color Clues

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Physical and Chemical Properties of Matter

The characteristics that enable us to distinguish one substance from another are called properties.

Physical Properties of Matter

A physical property is ...

atomic-radii-and-effective-nuclear-charge

Atomic Radii and Effective Nuclear Charge

The elements in groups of the periodic table exhibit similar chemical behavior. This similarity occurs because the members of a group have the same number ...

Ionic Radii

Ionic radius is the measure used to describe the size of an ion. A cation always has fewer electrons and the same number of protons as the parent atom; it ...

Ionization Energy

The amount of energy required to remove the most loosely bound electron from a gaseous atom in its ground state is called its first ionization energy ...

Electron Affinity

The electron affinity (EA) is the energy change for adding an electron to a gaseous atom to form an anion (negative ion).



This process can be either ...

Alkali Metals

Group 1 elements are soft and shiny metallic solids. They are malleable, ductile, and good conductors of heat and electricity. The melting points of the ...

Halogens

Group 17 elements, known as halogens, are nonmetals. At room temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine a solid. ...

Use patterns within the Periodic Table to predict the relative physical and chemical properties of elements.

IPC.7.B

Science concepts. The student knows that relationships exist between the structure and properties of matter. The student is expected to:

Flame Test Metal Color Clues

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