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

K12 Standards

Texas Essential Knowledge and Skills

High School

Chemistry and Physics

IPC.7

IPC.7.E

Metal Flame Emission

O teste de chama é uma técnica analítica em que uma amostra é aplicada a uma chama e o espectro de emissão característico é usado para identificar diferentes elementos. Quando essa técnica é usada para identificar espécies de metal, ela é chamada de teste de emissão de chama de metal. Quando energia suficiente é aplicada a alguns metais por meio de uma chama quente, eles emitem luz com um comprimento de onda ou cor característicos. Você pode ver claramente esse fenômeno ao assistir a uma queima de fogos de artifício.
Metais diferentes emitem cores diferentes. Assim, podemos usar a cor da luz emitida para determinar o metal presente. Mas antes de nos aprofundarmos na técnica, vamos dar um passo para trás. Os átomos têm vários níveis de energia para seus elétrons, que são diferentes para cada elemento.
Quando um elétron está em seu nível de energia mais baixo possível, diz-se que está em seu estado fundamental. Quando um átomo absorve energia, ele fica excitado e os elétrons no átomo se movem do estado fundamental para um nível de energia mais alto. Quando os elétrons relaxam de volta a um estado inferior, ou ao estado fundamental, o excesso de energia ganho é liberado na forma de luz emitida.
O comprimento de onda da luz emitida depende do nível de energia para o qual o elétron foi excitado e do nível para o qual ele relaxa de volta. Este comprimento de onda emitido, ou cor da luz, é específico para o átomo presente e é usado para identificar uma amostra de metal no teste de emissão de chama de metal.
No teste de emissão de chama de metal, aplicamos uma amostra de metal a uma chama quente e observamos a cor da luz emitida. Por exemplo, o bário emite uma cor verde-amarelada na chama, enquanto o cobre emite um verde-azulado e o potássio um roxo-rosado.
Agora, uma amostra na verdade consiste no metal, íons metálicos, óxidos metálicos, hidróxidos metálicos e sais metálicos. E como átomos e moléculas absorvem e liberam energia de maneira diferente, a luz emitida na verdade contém uma faixa de comprimentos de onda e intensidades formando um espectro de emissão.
Um espectrofotômetro é usado para medir a faixa de comprimentos de onda da luz emitida. 
Neste laboratório, você usará o teste de emissão de chama de metal para identificar vários metais e, em seguida, analisar a luz emitida e absorvida usando um espectrofotômetro.

emissão de chama de metal

<h4>Emissão de chama de metal</h4>
O teste de chama é uma técnica analítica em que uma amostra é colocada em uma chama e a cor característica da chama é usada para identificar a substância. Cada elemento tem uma emissão de luz característica quando colocado em uma chama, o que significa que cada elemento produz uma cor única. Esse fenômeno é usado em exibições de fogos de artifício, onde a cor dos fogos de artifício corresponde a uma característica específica de um metal. A emissão de luz colorida de uma amostra em chamas é o resultado direto do componente metálico absorvendo energia devido à excitação da chama e emitindo luz como resultado.
<h4>Excitação de elétrons</h4>
Quando uma espécie atômica ou molecular absorve energia, a energia é usada de quatro maneiras diferentes. Primeiro, a energia é usada na tradução, fazendo com que as moléculas se movam mais rápido. Em segundo lugar, a energia é usada na vibração, o que faz com que a distância entre as espécies mude rapidamente. Terceiro, a energia causa rotação, que induz a rotação dos átomos em torno das ligações na molécula. Finalmente, a energia absorvida resulta em excitação de elétrons, o que faz com que os elétrons se movam para um nível de energia mais alto do estado mais estável ou fundamental.
De acordo com o modelo de Bohr de hidrogênio, os elétrons em um átomo existem em estados discretos, que correspondem a camadas ou orbitais individuais ao redor do núcleo. O estado de energia mais baixo é chamado de estado fundamental e é representado pela notação de n = 1. Os estados de energia excitados têm energias mais altas e são representados pela notação de n = 2, 3, 4, etc.
Para que os elétrons se movam para um estado de energia mais alto, eles devem absorver uma quantidade de energia igual à diferença entre seu estado fundamental e o estado de energia mais alto. Por exemplo, se um elétron absorve uma quantidade de energia igual à diferença entre o estado fundamental e o nível de energia n=3, o elétron se moverá para o nível de energia n=3. Um elétron pode relaxar espontaneamente de volta ao estado fundamental ou a qualquer outro nível de energia inferior. Quando isso ocorre, um fóton é emitido, liberando a energia absorvida.
A energia liberada é emitida na forma de luz. A luz emitida tem uma energia característica e, portanto, comprimento de onda, que se correlaciona com os níveis de energia do átomo. A luz visível, que é a luz que os humanos podem ver com os olhos, varia de cerca de 400 nm a 700 nm no espectro eletromagnético.
As absorções e emissões atômicas são comprimentos de onda discretos, chamados linhas. Essas linhas são características únicas de um elemento, como um código de barras, e podem ser usadas para identificar o elemento.
<h4>Teste de emissão de chama metálica</h4>
No teste de emissão de chama de metal, uma amostra de metal é colocada em uma chama. A chama fornece a energia para excitar os elétrons a um nível de energia mais alto. À medida que os elétrons relaxam de volta ao estado fundamental, a luz é emitida com uma energia específica em relação aos níveis de energia dos átomos na amostra. Como átomos diferentes têm níveis de energia diferentes, a energia absorvida e emitida de uma amostra e, portanto, o comprimento de onda, é específica para a amostra.
Os metais têm comprimentos de onda de emissão atômica característicos na faixa visível que são facilmente determinados por inspeção visual. Por exemplo, o lítio emite uma cor vermelha, o sódio emite uma cor amarela, o potássio emite uma cor rosa-púrpura e o bário emite uma cor verde-amarelada.
Embora as emissões atômicas sejam comprimentos de onda ou linhas discretas, a maioria das amostras de metais contém não apenas o metal, mas também vários íons, óxidos e sais metálicos. Como cada átomo absorve e emite um comprimento de onda característico de luz, a luz absorvida e emitida do teste de chama contém uma faixa de comprimentos de onda. Assim, os espectros de absorção e emissão atômica podem ser medidos para a amostra usando um espectrofotômetro.
Os comprimentos de onda e as formas dos espectros são únicos para cada substância. Por exemplo, a intensidade relativa das características no espectro depende da concentração da espécie. As intensidades absolutas dependem da distância da amostra ao espectrofotômetro.
<h4>Referências</h4>
<ol>
	<li style="font-size:17px">Kotz, J.C., Treichel Jr, P.M., Townsend, J.R. (2012). Química e Reatividade Química. Belmont, CA: Brooks / Cole, Cengage Learning.</li>
	<li style="font-size:17px">Silderberg, M.S. (2009). Química: A Natureza Molecular da Matéria e da Mudança. Boston, MA: Colina McGraw.</li>
	<li style="font-size:17px">Harris, D.C. (2015). Análise Química Quantitativa. Nova York, NY: W.H. Freeman and Company.</li>
</ol>

Emissão de chama de metal

Emissão de chama de metal
O teste de chama é uma técnica analítica em que uma amostra é colocada em uma chama e a cor característica da chama é usada 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

lab techniques

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Graphs, Curve Fit, and Standard Deviation

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Gas Laws Behind the Ideal Gas Equation

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acid and base concentrations

Acids, Bases, and pH in Titration

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buffers

Buffer pH and the Common Ion Effect

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solubility

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metal flame emission

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...

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beer's law

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concentration dependence

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temperature dependence

Reaction Rate, Arrhenius, and Catalysts

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galvanic cells

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proper lab notebook keeping

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basic organic chemistry techniques

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melting points

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boiling points

Boiling Point and Vapor Pressure

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Purifying Crystals by Solubility

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extraction

Separating Mixtures with Solvent Extraction

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simple distillation

Separating Liquids by Boiling Point

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steam distillation

Steam Distillation and Low-Boiling Separation

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thin-layer chromatography

TLC Separation by Polarity

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column chromatography

Separating Mixtures by Polarity

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synthesis of luminol

Luminol Chemiluminescence in Forensics

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esterification

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identification of unknown aldehydes and ketones

identification-of-unknown-aldehydes-and-ketones

Carbonyl Tests for Aldehydes and Ketones

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uv-vis spectroscopy of dyes

How Dyes Absorb Visible Light

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identifying alcohols

Alcohol Tests for Primary, Secondary, and Tertiary

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chemistry

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Learn how flame testing identifies metals by color, why electrons emit light in the flame, and how spectra reveal each element's unique wavelengths.

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The earliest recorded discussion of the basic structure of matter comes from ancient Greek philosophers. Leucippus and Democritus argued that all matter ...

Subatomic Particles

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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. ...

Noble Gases


The elements in group 18 are noble gases (helium, neon, argon, krypton, xenon, and radon). They earned the name &ldquo;noble&rdquo; because they were ...

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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