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

K12 Standards

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Chemistry and Physics

IPC.7

IPC.7.E

Metal Flame Emission

Il test di fiamma è una tecnica analitica in cui un campione viene applicato a una fiamma e lo spettro di emissione caratteristico viene utilizzato per identificare diversi elementi. Quando questa tecnica viene utilizzata per identificare le specie metalliche, si parla di test di emissione di fiamma metallica. Quando viene applicata energia sufficiente ad alcuni metalli attraverso una fiamma calda, emettono luce con una lunghezza d'onda o un colore caratteristico. Questo fenomeno è chiaramente visibile quando si guarda uno spettacolo pirotecnico.
Metalli diversi emettono colori diversi. Pertanto, possiamo utilizzare il colore della luce emessa per determinare il metallo presente. Ma prima di addentrarci ulteriormente nella tecnica, facciamo un passo indietro. Gli atomi hanno più livelli di energia per i loro elettroni, che sono diversi per ogni elemento.
Quando un elettrone è al suo livello di energia più basso possibile, si dice che è al suo stato fondamentale. Quando un atomo assorbe energia, si eccita e gli elettroni nell'atomo si spostano dallo stato fondamentale a un livello di energia più elevato. Quando gli elettroni si rilassano di nuovo in uno stato inferiore, o stato fondamentale, l'energia in eccesso guadagnata viene rilasciata sotto forma di luce emessa.
La lunghezza d'onda della luce emessa dipende dal livello di energia a cui l'elettrone è stato eccitato e dal livello a cui si rilassa di nuovo. Questa lunghezza d'onda emessa, o colore della luce, è specifica per l'atomo presente e viene utilizzata per identificare un campione di metallo nel test di emissione di fiamma metallica.
Nel test di emissione della fiamma metallica, applichiamo un campione di metallo a una fiamma calda e osserviamo il colore della luce emessa. Ad esempio, il bario emetterà un colore verde-giallastro nella fiamma, mentre il rame emette blu-verde e il potassio un viola-rosato.
Ora, un campione è costituito dal metallo, dagli ioni metallici, dagli ossidi metallici, dagli idrossidi metallici e dai sali metallici. E poiché gli atomi e le molecole assorbono e rilasciano energia in modo diverso, la luce emessa contiene in realtà una gamma di lunghezze d'onda e intensità che formano uno spettro di emissione.
Uno spettrofotometro viene utilizzato per misurare la gamma di lunghezze d'onda della luce emessa. 
In questo laboratorio, utilizzerai il test di emissione di fiamma del metallo per identificare vari metalli e quindi analizzare la luce emessa e assorbita utilizzando uno spettrofotometro.

emissione di fiamma metallica

<h4>Emissione di fiamma metallica</h4>
Il test della fiamma è una tecnica analitica in cui un campione viene posto in una fiamma e il caratteristico colore della fiamma viene utilizzato per identificare la sostanza. Ogni elemento ha una caratteristica emissione di luce quando viene inserito in una fiamma, il che significa che ogni elemento produce un colore unico. Questo fenomeno viene utilizzato nei fuochi d'artificio, dove il colore dei fuochi d'artificio corrisponde a una caratteristica specifica di un metallo. L'emissione di luce colorata da un campione in fiamme è il risultato diretto dell'assorbimento dell'energia da parte del componente metallico dovuto all'eccitazione della fiamma e dell'emissione di luce di conseguenza.
<h4>Eccitazione elettronica</h4>
Quando una specie atomica o molecolare assorbe energia, l'energia viene utilizzata in quattro modi diversi. In primo luogo, l'energia viene utilizzata nella traslazione, facendo muovere le molecole più velocemente. In secondo luogo, l'energia viene utilizzata nella vibrazione, che fa sì che la distanza tra le specie cambi rapidamente. In terzo luogo, l'energia provoca la rotazione, che induce la rotazione degli atomi attorno ai legami nella molecola. Infine, l'energia assorbita si traduce in eccitazione degli elettroni, che fa sì che gli elettroni si spostino a un livello di energia più elevato dallo stato più stabile o fondamentale.
Secondo il modello di Bohr dell'idrogeno, gli elettroni in un atomo esistono in stati discreti, che corrispondono a singoli gusci o orbitali attorno al nucleo. Lo stato energetico più basso è chiamato stato fondamentale ed è rappresentato dalla notazione di n = 1. Gli stati di energia eccitata hanno energie più elevate e sono rappresentati dalla notazione di n = 2, 3, 4, ecc.
Affinché gli elettroni si muovano verso uno stato energetico più elevato, devono assorbire una quantità di energia pari alla differenza tra il suo stato fondamentale e lo stato energetico più elevato. Ad esempio, se un elettrone assorbe una quantità di energia pari alla differenza tra lo stato fondamentale e il livello di energia n=3, l'elettrone si sposterà al livello di energia n=3. Un elettrone può rilassarsi spontaneamente fino allo stato fondamentale o a qualsiasi altro livello di energia inferiore. Quando ciò si verifica, viene emesso un fotone, che rilascia l'energia assorbita.
L'energia rilasciata viene emessa sotto forma di luce. La luce emessa ha un'energia caratteristica, e quindi una lunghezza d'onda, che è correlata ai livelli di energia dell'atomo. La luce visibile, che è la luce che gli esseri umani possono vedere con i loro occhi, varia da circa 400 nm a 700 nm sullo spettro elettromagnetico.
Gli assorbimenti atomici e le emissioni sono lunghezze d'onda discrete, chiamate linee. Queste linee sono caratteristiche uniche di un elemento, come un codice a barre, e possono essere utilizzate per identificare l'elemento.
<h4>Test di emissione di fiamma in metallo</h4>
Nel test di emissione di fiamma metallica, un campione di metallo viene posto in una fiamma. La fiamma fornisce l'energia per eccitare gli elettroni a un livello di energia più elevato. Quando gli elettroni si rilassano tornando allo stato fondamentale, la luce viene emessa con un'energia specifica relativa ai livelli di energia degli atomi nel campione. Poiché atomi diversi hanno livelli di energia diversi, l'energia assorbita ed emessa da un campione, e quindi la lunghezza d'onda, è specifica per il campione.
I metalli hanno lunghezze d'onda di emissione atomica caratteristiche nell'intervallo visibile che possono essere facilmente determinate dall'ispezione visiva. Ad esempio, il litio emette un colore rosso, il sodio emette un colore giallo, il potassio emette un colore rosa-viola e il bario emette un colore giallo-verde.
Mentre le emissioni atomiche sono lunghezze d'onda o linee discrete, la maggior parte dei campioni di metalli contiene non solo il metallo, ma anche vari ioni, ossidi e sali metallici. Poiché ogni atomo assorbe ed emette una lunghezza d'onda caratteristica della luce, la luce assorbita ed emessa dal test della fiamma contiene una gamma di lunghezze d'onda. Pertanto, gli spettri di assorbimento atomico e di emissione possono essere misurati per il campione utilizzando uno spettrofotometro.
Le lunghezze d'onda e le forme degli spettri sono uniche per ogni sostanza. Ad esempio, l'intensità relativa delle caratteristiche nello spettro dipende dalla concentrazione della specie. Le intensità assolute dipendono dalla distanza tra il campione e lo spettrofotometro.
<h4>referenze</h4>
<ol>
	<li style="font-size:17px">Kotz, J.C., Treichel Jr, P.M., Townsend, J.R. (2012). Chimica e reattività chimica. Belmont, CA: Brooks/Cole, Cengage Learning.</li>
	<li style="font-size:17px">Silderberg, M.S. (2009). Chimica: la natura molecolare della materia e il cambiamento. Boston, MA: McGraw Hill.</li>
	<li style="dimensione del carattere:17px">Harris, D.C. (2015). Analisi chimica quantitativa. New York, NY: W.H. Freeman e compagnia.</li>
</ol>

Emissione di fiamma metallica

Emissione di fiamma metallica
Il test della fiamma è una tecnica analitica in cui un campione viene posto in una fiamma e il colore caratteristico della fiamma viene utilizzato per identificare ...

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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

Measuring with Accuracy in the Lab

Measuring with accuracy in the lab starts with careful records, the right tools, and correct reading of data. Scientists use lab notebooks to record how an experiment was done. These notes include the amounts of materials used and each step of the procedure. Without that record, an experiment cannot be repeated in the same way. Balances and glassware are used to measure solids and liquids for experiments. The precision of a measurement depends on the equipment used. Digital balances show the...

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Graphs, Curve Fit, and Standard Deviation

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stoichiometry, product yield, and limiting reactants

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Balancing Equations and Reactant Limits

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redox reactions

Oxidation States in Redox Reactions

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ideal gas law

Gas Laws Behind the Ideal Gas Equation

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acid and base concentrations

Acids, Bases, and pH in Titration

Acids, bases, and pH explain how acidic or basic a solution is. An Arrhenius acid releases hydrogen ions when it dissolves in water, while an Arrhenius base releases hydroxide ions. These reactions also create conjugate partners: an acid forms a conjugate base after losing hydrogen, and a base forms a conjugate acid after losing hydroxyl. Every acid has a conjugate base, and every base has a conjugate acid. pH measures the amount of hydrogen ions in a solution. The pH scale runs from 0 to 14...

buffers

Buffer pH and the Common Ion Effect

Buffer solutions help keep pH steady when acids or bases are added. In water, an Arrhenius acid (HA) dissociates into hydrogen ions, H+, and a conjugate base, A-. More hydrogen ions make a solution more acidic and lower its pH. An Arrhenius base (BOH) dissociates into a conjugate acid, B+, and hydroxide ions, OH-. Strong acids and strong bases usually change pH a lot because they react completely in water and raise the amount of H+ or OH-. Buffers reduce those pH changes. A buffer usually...

enthalpy of reaction

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solubility

Solubility in Water and Other Solvents

Solubility describes how much of a solute can dissolve in a specific solvent. It is usually reported as solute mass per solvent volume or as solute mass per solvent mass. For example, sodium chloride has a solubility of 36 g per 100 mL of water at room temperature. If solubility is given by solvent mass, that mass must be converted to volume for later calculations. Temperature changes solubility. Sodium carbonate dissolves at about 7 g per 100 mL of water at 0 °C, 22 g per 100 mL at room...

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...

balmer series

Hydrogen Emission Lines

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beer's law

Absorbance Spectra and Beer-Lambert Analysis

Absorbance spectra and the Beer-Lambert Law show how light can be used to study molecules in solution. When light hits a substance, it may be absorbed, transmitted, or reflected. A substance often interacts with a range of wavelengths, and each wavelength can affect the molecules or atoms in a different way. When a molecule absorbs light, that energy can be used for translation, vibration, rotation, or electron excitement. Electron excitement is especially important in spectroscopy because it...

concentration dependence

Reaction Order and Rate Constants

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temperature dependence

Reaction Rate, Arrhenius, and Catalysts

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galvanic cells

Battery Power from Redox Reactions

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electrolytic 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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recrystallization

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

Separating liquids by boiling point is the goal of distillation. A miscible mixture contains liquids that mix evenly, and it can be heated so that the more volatile liquid evaporates first. Volatility is a liquid’s tendency to vaporize, and boiling begins when bubbles form in the liquid phase. In a closed container, liquid and vapor can reach equilibrium, which means the rate of vaporization equals the rate of condensation. The pressure from the vapor above the liquid is called vapor pressure.

steam distillation

Steam Distillation and Low-Boiling Separation

Steam distillation is a separation method for temperature-sensitive organic compounds. It works best when the organic compound is immiscible in water, meaning the two liquids do not mix. The method helps remove the organic molecule from a non-volatile contaminant without using the higher temperatures needed for many other separations. In steam distillation, the immiscible mixture is heated until both water and the volatile organic compound distill together. The vapor rises to a condenser,...

thin-layer chromatography

TLC Separation by Polarity

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column chromatography

Separating Mixtures by Polarity

Column chromatography separates compounds in an organic chemistry lab by using differences in physical properties. It is especially useful for microscale separations when less than 10 grams of material is available for analysis. The method can separate a mixture based on solubility, polarity, hydrophobicity, size, and charge. Any chromatography system has three main parts: the stationary phase, the mobile phase, and the sample mixture. In column chromatography, the stationary phase is usually...

hydrolysis of an ester

Soap Formation from Triglycerides

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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

Dyes absorb visible light because their molecular structure lets them interact with specific wavelengths. When light hits a substance, some light is absorbed and the rest is reflected or transmitted. The color we see depends on the wavelength that is reflected. A blue substance reflects blue light, around 430 to 480 nm, and absorbs the complementary orange region, around 590 to 630 nm. Compounds that do not absorb in the visible range appear colorless to the human eye. Light also has energy and...

identifying alcohols

Alcohol Tests for Primary, Secondary, and Tertiary

Alcohol tests can help sort alcohols by structure and reactivity. Alcohols are organic molecules with a hydroxyl group attached to an alkyl or aryl group, written as ROH. If the carbon with the hydroxyl group has one R group, the alcohol is primary. If it has two R groups, it is secondary. If it has three R groups, it is tertiary. Alcohols can also be aromatic when they contain a benzene ring. Phenol is the simplest aromatic alcohol. To identify an alcohol, chemists can use its chemical...

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.

Flame Test Metal Color Clues | JoVE K12

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Preparati a insegnare Emissione di fiamma metallica con questa guida per istruttori di 2 minuti. Copre i passaggi chiave di preparazione per il laboratorio Chemistry su JoVE Lab Manual.

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The Atomic Theory of Matter

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

Subatomic Particles

Dalton was only partially correct about the particles that make up matter. All matter is composed of atoms, and atoms are composed of three smaller ...

Elements: Chemical Symbols and Isotopes

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Ions and Ionic Charges

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The Periodic Table

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Atomic Mass

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Molar Mass

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Periodic Classification of the Elements

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Types of Chemical Bonds

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Ionic Bonding and Electron Transfer

Ions are atoms or molecules bearing an electrical charge. A cation (a positive ion) forms when a neutral atom loses one or more electrons from its valence ...

The Born-Haber Cycle

Lattice Energy&#xA0;

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Trends in Lattice Energy: Ion Size and Charge

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Covalent Bonding and Lewis Structures

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Electronegativity

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Electronegativity values of ...

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Bond Polarity, Dipole Moment, and Percent Ionic Character

Bond Polarity

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Lewis Structures of Molecular Compounds and Polyatomic Ions

To draw Lewis structures for complicated molecules and molecular ions, it is helpful to follow a step-by-step procedure as outlined:


	Determine the ...

Bond Energies and Bond Lengths

Stable molecules exist because covalent bonds hold the atoms together. The strength of a covalent bond is measured by the energy required to break it, ...

Bonding in Metals

Metallic bonds are formed between two metal atoms. A simplified model to describe metallic bonding has been developed by Paul Dr&#xFC;de called the ...

Model basic atomic structure and relate an element's atomic structure to its bonding, reactivity, and placement on the Periodic Table.

IPC.7.A

physical-and-chemical-properties-of-matter

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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