Flame test

A flame test is an analytic procedure used in chemistry to detect the presence of certain elements, primarily metal ions, based on each element's characteristic emission spectrum. The color of flames in general also depends on temperature; see flame color.

Flame test
The flame test carried out on a copper halide. The characteristic bluish-green color of the flame is due to the copper.
A Student Conducting the Chemical Experiment using Crucible
A flame test showing the presence of Lithium.
Bunsen burner flame types
Different flame of Bunsen burner, depending on air flow through the valve:
  1. air valve closed
  2. air valve nearly fully closed
  3. air valve semi-opened
  4. air valve maximally opened
Flametest--.swn
Gas flame

Process

The test involves introducing a sample of the element or compound to a hot, non-luminous flame, and observing the color of the flame that results. The idea of the test is that sample atoms evaporate and since they are hot, they emit light when being in flame. Bulk sample emits light too, but its light is not good for analysis. Bulk sample emits light primarily due to the motion of the atoms, therefore its spectrum is broad, consisting of a broad range of colors. Separate atoms of a sample present in the flame can emit only due to electronic transitions between different atomic energy levels. Those transitions emit light of very specific frequencies, characteristic of the chemical element itself. Therefore, the flame gets the color, which is primarily determined by properties of the chemical element of the substance being put into flame. The flame test is a relatively easy experiment to set up and thus is often demonstrated or carried out in science classes in schools.

Samples are usually held on a platinum wire cleaned repeatedly with hydrochloric acid to remove traces of previous analytes.[1] The compound is usually made into a paste with concentrated hydrochloric acid, as metal halides, being volatile, give better results. Different flames should be tried to avoid wrong data due to "contaminated" flames, or occasionally to verify the accuracy of the color. In high-school chemistry courses, wooden splints are sometimes used, mostly because solutions can be dried onto them, and they are inexpensive. Nichrome wire is also sometimes used.[1] When using a splint, one must be careful to wave the splint through the flame rather than holding it in the flame for extended periods, to avoid setting the splint itself on fire. The use of cotton swab[2] or melamine foam (used in "eraser" cleaning sponges)[3] as a support have also been suggested.

Sodium is a common component or contaminant in many compounds and its spectrum tends to dominate over others. The test flame is often viewed through cobalt blue glass to filter out the yellow of sodium and allow for easier viewing of other metal ions.

Results

The flame test is relatively quick and simple to perform and can be carried out with the basic equipment found in most chemistry laboratories. However, the range of elements positively detectable under these conditions is small, as the test relies on the subjective experience of the experimenter rather than any objective measurements. The test has difficulty detecting small concentrations of some elements, while too strong a result may be produced for certain others, which tends to cause fainter colors to not appear.

Although the flame test only gives qualitative information, not quantitative data about the proportion of elements in the sample, quantitative data can be obtained by the related techniques of flame photometry or flame emission spectroscopy. Flame atomic absorption spectroscopy Instruments, made by e.g. PerkinElmer or Shimadzu, can be operated in emission mode according to the instrument manuals.[4]

Common elements

Some common elements and their corresponding colors are:

Symbol Name Color Image
Al Aluminium Silver-white, in very high temperatures such as an electric arc, light blue
As Arsenic Blue FlammenfärbungAs.jpg
B Boron Bright green FlammenfärbungB.png
Ba Barium Pale/Apple green
Be Beryllium White
Bi Bismuth Azure
Ca Calcium Brick red, light green as seen through blue glass FlammenfärbungCa.png
Cd Cadmium Brick red
Ce Cerium Yellow
Co Cobalt Silver-white
Cr Chromium Silver-white
Cs Caesium Blue-violet Flame test of CsCl (B)
Cu(I) Copper(I) Bluish-green
Cu(II) Copper(II) (non-halide) Green Flame test on copper sulfate
Cu(II) Copper(II) (halide) Blue-green
Ge Germanium Pale blue
Fe(II) Iron(II) Gold, when very hot such as an electric arc, bright blue, or green turning to orange-brown
Fe(III) Iron(III) Orange-brown An iron (III) flame, generated using the thermite reaction
Hf Hafnium White
Hg Mercury Red
In Indium Indigo/Blue
K Potassium Lilac FlammenfärbungK.png
Li Lithium crimson red; invisible through green glass FlammenfärbungLi.png
Mg Magnesium (none), but for burning Mg metal Intense White
Mn (II) Manganese (II) Yellowish green
Mo Molybdenum Yellowish green
Na Sodium Intense yellow; invisible through cobalt blue glass Flametest--Na.swn.jpg
Nb Niobium Green or blue
Ni Nickel Silver-white (sometimes reported as colorless)
P Phosphorus Pale bluish green
Pb Lead Blue/white FlammenfärbungPb.png
Ra Radium Crimson
Rb Rubidium Red-violet Die Flammenfärbung des Rubidium.jpg
Sb Antimony Pale green FlammenfärbungSb.png
Sc Scandium Orange
Se Selenium Azure
Sn Tin Blue-white
Sr Strontium Crimson to Scarlet, yellowish through green glass and violet through blue cobalt glass FlammenfärbungSr.png
Ta Tantalum Blue
Te Tellurium Pale green
Ti Titanium Silver-white
Tl Thallium Pure green
V Vanadium Yellowish Green
W Tungsten Green
Y Yttrium Carmine, Crimson, or Scarlet
Zn Zinc Colorless (sometimes reported as bluish-green) Zinc burning
Zr Zirconium Mild red

Gold, silver, platinum, palladium, and a number of other elements do not produce a characteristic flame color, although some may produce sparks (as do metallic titanium and iron); salts of beryllium and gold reportedly deposit pure metal on cooling.

See also

References

  1. ^ a b Jim Clark (2005). "Flame Tests". Chemguide.
  2. ^ Sanger, Michael J.; Phelps, Amy J.; Catherine Banks (2004). "Simple Flame Test Techniques Using Cotton Swabs". Journal of Chemical Education. 81 (7): 969. Bibcode:2004JChEd..81..969S. doi:10.1021/ed081p969
  3. ^ Landis, Arthur M.; Davies, Malonne I.; Landis, Linda; Nicholas c. Thomas (2009). ""Magic Eraser" Flame Tests". Journal of Chemical Education. 86 (5): 577. Bibcode:2009JChEd..86..577L. doi:10.1021/ed086p577
  4. ^ "Atomic Absorption (AA)". Perkin Elmer. Retrieved 2 May 2013.

External links

Alkaline earth metal

The alkaline earth metals are six chemical elements in group 2 of the periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). The elements have very similar properties: they are all shiny, silvery-white, somewhat reactive metals at standard temperature and pressure.Structurally, they have in common an outer s- electron shell which is full;

that is, this orbital contains its full complement of two electrons, which these elements readily lose to form cations with charge +2, and an oxidation state of +2.All the discovered alkaline earth metals occur in nature, although radium occurs only through the decay chain of uranium and thorium and not as a primordial element. Experiments have been conducted to attempt the synthesis of element 120, the next potential member of the group, but they have all met with failure.

Amblygonite

Amblygonite ( ) is a fluorophosphate mineral, (Li,Na)AlPO4(F,OH), composed of lithium, sodium, aluminium, phosphate, fluoride and hydroxide. The mineral occurs in pegmatite deposits and is easily mistaken for albite and other feldspars. Its density, cleavage and flame test for lithium are diagnostic. Amblygonite forms a series with montebrasite, the low fluorine endmember. Geologic occurrence is in granite pegmatites, high-temperature tin veins, and greisens. Amblygonite occurs with spodumene, apatite, lepidolite, tourmaline, and other lithium-bearing minerals in pegmatite veins. It contains about 10% lithium, and has been utilized as a source of lithium. The chief commercial sources have historically been the deposits of California and France.

Analytical chemistry

Analytical chemistry studies and uses instruments and methods used to separate, identify, and quantify matter. In practice, separation, identification or quantification may constitute the entire analysis or be combined with another method. Separation isolates analytes. Qualitative analysis identifies analytes, while quantitative analysis determines the numerical amount or concentration.

Analytical chemistry consists of classical, wet chemical methods and modern, instrumental methods. Classical qualitative methods use separations such as precipitation, extraction, and distillation. Identification may be based on differences in color, odor, melting point, boiling point, radioactivity or reactivity. Classical quantitative analysis uses mass or volume changes to quantify amount. Instrumental methods may be used to separate samples using chromatography, electrophoresis or field flow fractionation. Then qualitative and quantitative analysis can be performed, often with the same instrument and may use light interaction, heat interaction, electric fields or magnetic fields. Often the same instrument can separate, identify and quantify an analyte.

Analytical chemistry is also focused on improvements in experimental design, chemometrics, and the creation of new measurement tools. Analytical chemistry has broad applications to forensics, medicine, science and engineering.

Category 5 cable

Category 5 cable, commonly referred to as Cat 5, is a twisted pair cable for computer networks. Since 2001, the variant commonly in use is the Category 5e specification (Cat 5e). The cable standard provides performance of up to 100 MHz and is suitable for most varieties of Ethernet over twisted pair up to 1000BASE-T (Gigabit Ethernet). Cat 5 is also used to carry other signals such as telephony and video.

This cable is commonly connected using punch-down blocks and modular connectors. Most Category 5 cables are unshielded, relying on the balanced line twisted pair design and differential signaling for noise rejection.

Colored fire

Colored fire is a common pyrotechnic effect used in stage productions, fireworks and by fire performers the world over. Generally, the color of a flame may be red, orange, blue, yellow, or white, and is dominated by blackbody radiation from soot and steam. When additional chemicals are added to the fuel burning, their atomic emission spectra can affect the frequencies of visible light radiation emitted - in other words, the flame appears in a different color dependent upon the chemical additives. Flame coloring is also a good way to demonstrate how fire changes when subjected to heat and how they also change the matter around them.To color their flames, pyrotechnicians will generally use metal salts. Specific combinations of fuels and co-solvents are required in order to dissolve the necessary chemicals. Color enhancers (usually chlorine donors) are frequently added too, the most common of which is polyvinyl chloride. A practical use of colored fire is the flame test, where metal cations are tested by placing the sample in a flame and analyzing the color produced.

Copper(II) sulfate

Copper(II) sulfate, also known as copper sulphate, are the inorganic compounds with the chemical formula CuSO4(H2O)x, where x can range from 0 to 5. The pentahydrate (x = 5) is the most common form. Older names for this compound include blue vitriol, bluestone, vitriol of copper, and Roman vitriol.The pentahydrate (CuSO4·5H2O), the most commonly encountered salt, is bright blue. It exothermically dissolves in water to give the aquo complex [Cu(H2O)6]2+, which has octahedral molecular geometry. The structure of the solid pentahydrate reveals a polymeric structure wherein copper is again octahedral but bound to four water ligands. The Cu(II)(H2O)4 centers are interconnected by sulfate anions to form chains. Anhydrous copper sulfate is a white powder.

Emission spectrum

The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted due to an atom or molecule making a transition from a high energy state to a lower energy state. The photon energy of the emitted photon is equal to the energy difference between the two states. There are many possible electron transitions for each atom, and each transition has a specific energy difference. This collection of different transitions, leading to different radiated wavelengths, make up an emission spectrum. Each element's emission spectrum is unique. Therefore, spectroscopy can be used to identify the elements in matter of unknown composition. Similarly, the emission spectra of molecules can be used in chemical analysis of substances.

Fire-safe polymers

Fire-safe polymers are polymers that are resistant to degradation at high temperatures. There is need for fire-resistant polymers in the construction of small, enclosed spaces such as skyscrapers, boats, and airplane cabins. In these tight spaces, ability to escape in the event of a fire is compromised, increasing fire risk. In fact, some studies report that about 20% of victims of airplane crashes are killed not by the crash itself but by ensuing fires. Fire-safe polymers also find application as adhesives in aerospace materials, insulation for electronics, and in military materials such as canvas tenting.Some fire-safe polymers naturally exhibit an intrinsic resistance to decomposition, while others are synthesized by incorporating fire-resistant additives and fillers. Current research in developing fire-safe polymers is focused on modifying various properties of the polymers such as ease of ignition, rate of heat release, and the evolution of smoke and toxic gases. Standard methods for testing polymer flammability vary among countries; in the United States common fire tests include the UL 94 small-flame test, the ASTM E 84 Steiner Tunnel, and the ASTM E 622 National Institute of Standards and Technology (NIST) smoke chamber. Research on developing fire-safe polymers with more desirable properties is concentrated at the University of Massachusetts Amherst and at the Federal Aviation Administration where a long-term research program on developing fire-safe polymers was begun in 1995. The Center for UMass/Industry Research on Polymers (CUMIRP) was established in 1980 in Amherst, MA as a concentrated cluster of scientists from both academia and industry for the purpose of polymer science and engineering research.

Flame

A flame (from Latin flamma) is the visible, gaseous part of a fire. It is caused by a highly exothermic reaction taking place in a thin zone. Very hot flames are hot enough to have ionized gaseous components of sufficient density to be considered plasma.

Group 12 element

Group 12, by modern IUPAC numbering, is a group of chemical elements in the periodic table. It includes zinc (Zn), cadmium (Cd) and mercury (Hg). The further inclusion of copernicium (Cn) in group 12 is supported by recent experiments on individual copernicium atoms. Formerly this group was named IIB (pronounced as "group two B", as the "II" is a Roman numeral) by CAS and old IUPAC system.The three group 12 elements that occur naturally are zinc, cadmium and mercury. They are all widely used in electric and electronic applications, as well as in various alloys. The first two members of the group share similar properties as they are solid metals under standard conditions. Mercury is the only metal that is a liquid at room temperature. While zinc is very important in the biochemistry of living organisms, cadmium and mercury are both highly toxic. As copernicium does not occur in nature, it has to be synthesized in the laboratory.

Max Steel

Max Steel is a line of action figures produced and owned by the toy company Mattel since 1999. The original figures based on the first TV series were similar to the original 12-inch G.I. Joe toys, consisting almost entirely of different versions of Max Steel, the main character, and one or two of his enemies, a couple of vehicles and two or three special packages. The original toy series ran from 1999–2012. At the end of that period, was substituted by a different series of toys with the same brand name, but with a change in quality and design intended to tie into the companion TV series in 2013. The 2013 line did not exhibit 1/6 scale of the original and reduced the number of articulations and action features of the figures.

Max Steel was simultaneously developed into an animated series of the same name, which originally aired from February 25, 2000, to January 15, 2002, followed by nine direct-to-video animated films, being released annually from 2004 to 2012. A reboot aired on Disney XD in the United States, where it had premiered on March 25, 2013.

Photoelectric flame photometer

A photoelectric flame photometer is a device used in inorganic chemical analysis to determine the concentration of certain metal ions, among them sodium, potassium, lithium, and calcium. Group 1 and Group 2 metals are quite sensitive to Flame Photometry due to their low excitation energies.

In principle, it is a controlled flame test with the intensity of the flame color quantified by photoelectric circuitry. The intensity of the colour will depend on the energy that had been absorbed by the atoms that was sufficient to vaporise them. The sample is introduced to the flame at a constant rate. Filters select which colours the photometer detects and exclude the influence of other ions. Before use, the device requires calibration with a series of standard solutions of the ion to be tested.

Flame photometry is crude but cheap compared to flame emission spectroscopy or ICP-AES, where the emitted light is analysed with a monochromator. Its status is similar to that of the colorimeter (which uses filters) compared to the spectrophotometer (which uses a monochromator). It also has the range of metals that could be analysed and the limit of detection are also considered

Rubidium

Rubidium is a chemical element with symbol Rb and atomic number 37. Rubidium is a soft, silvery-white metallic element of the alkali metal group, with a standard atomic weight of 85.4678. Elemental rubidium is highly reactive, with properties similar to those of other alkali metals, including rapid oxidation in air. On Earth, natural rubidium comprises two isotopes: 72% is the stable isotope, 85Rb; 28% is the slightly radioactive 87Rb, with a half-life of 49 billion years—more than three times longer than the estimated age of the universe.

German chemists Robert Bunsen and Gustav Kirchhoff discovered rubidium in 1861 by the newly developed technique, flame spectroscopy.

Rubidium's compounds have various chemical and electronic applications. Rubidium metal is easily vaporized and has a convenient spectral absorption range, making it a frequent target for laser manipulation of atoms.

Rubidium is not a known nutrient for any living organisms. However, rubidium ions have the same charge as potassium ions, and are actively taken up and treated by animal cells in similar ways.

Sodium

Sodium is a chemical element with symbol Na (from Latin natrium) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table, because it has a single electron in its outer shell that it readily donates, creating a positively charged ion—the Na+ cation. Its only stable isotope is 23Na. The free metal does not occur in nature, and must be prepared from compounds. Sodium is the sixth most abundant element in the Earth's crust and exists in numerous minerals such as feldspars, sodalite, and rock salt (NaCl). Many salts of sodium are highly water-soluble: sodium ions have been leached by the action of water from the Earth's minerals over eons, and thus sodium and chlorine are the most common dissolved elements by weight in the oceans.

Sodium was first isolated by Humphry Davy in 1807 by the electrolysis of sodium hydroxide. Among many other useful sodium compounds, sodium hydroxide (lye) is used in soap manufacture, and sodium chloride (edible salt) is a de-icing agent and a nutrient for animals including humans.

Sodium is an essential element for all animals and some plants. Sodium ions are the major cation in the extracellular fluid (ECF) and as such are the major contributor to the ECF osmotic pressure and ECF compartment volume. Loss of water from the ECF compartment increases the sodium concentration, a condition called hypernatremia. Isotonic loss of water and sodium from the ECF compartment decreases the size of that compartment in a condition called ECF hypovolemia.

By means of the sodium-potassium pump, living human cells pump three sodium ions out of the cell in exchange for two potassium ions pumped in; comparing ion concentrations across the cell membrane, inside to outside, potassium measures about 40:1, and sodium, about 1:10. In nerve cells, the electrical charge across the cell membrane enables transmission of the nerve impulse—an action potential—when the charge is dissipated; sodium plays a key role in that activity.

Splint (laboratory equipment)

A splint is a simple piece of equipment used in scientific laboratories. Splints are typically long, thin strips of wood, about 6 inches (150 mm) long and ¼ inch (6 mm) wide, and are consumable but inexpensive. They are typically used for tasks such as lighting bunsen burners, as the length of the splint allows a flame to be lit without risk to the user's hand, should the burner flare back. Another use for splints are chemical identification of various gases, and splints are also used to teach simple chemical principles in schools.

Strontium

Strontium is the chemical element with symbol Sr and atomic number 38. An alkaline earth metal, strontium is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is exposed to air. Strontium has physical and chemical properties similar to those of its two vertical neighbors in the periodic table, calcium and barium. It occurs naturally mainly in the minerals celestine and strontianite, and is mostly mined from these. While natural strontium is stable, the synthetic 90Sr isotope is radioactive and is one of the most dangerous components of nuclear fallout, as strontium is absorbed by the body in a similar manner to calcium. Natural stable strontium, on the other hand, is not hazardous to health.

Both strontium and strontianite are named after Strontian, a village in Scotland near which the mineral was discovered in 1790 by Adair Crawford and William Cruickshank; it was identified as a new element the next year from its crimson-red flame test color. Strontium was first isolated as a metal in 1808 by Humphry Davy using the then-newly discovered process of electrolysis. During the 19th century, strontium was mostly used in the production of sugar from sugar beet (see strontian process). At the peak of production of television cathode ray tubes, as much as 75 percent of strontium consumption in the United States was used for the faceplate glass. With the replacement of cathode ray tubes with other display methods, consumption of strontium has dramatically declined.

Strontium bromide

Strontium bromide is a chemical compound with a formula SrBr2. At room temperature it is a white, odorless, crystalline powder. Strontium bromide burns bright red in a flame test. It is used in flares and also has some pharmaceutical uses.

Thomas Melvill

Thomas Melvill(e) (1726 – December 1753) was a Scottish natural philosopher, who was active in the fields of spectroscopy and astronomy.The son of Helen Whytt and the Rev Andrew Melville, minister of Monimail (d. 29 July 1736), Thomas was a student at Glasgow University. In 1749, with Alexander Wilson, his landlord and later the first professor of astronomy at Glasgow University, made the first recorded use of kites in meteorology. They measured air temperature at various levels above the ground simultaneously with a train of kites.

He most notably delivered a lecture entitled Observations on light and colours to the Medical Society of Edinburgh in 1752, in which he described what has been seen as the first flame test. In it he described how he had used a prism to observe a flame coloured by various salts. He reported that a yellow line was always seen at the same place in the spectrum; this was derived from the sodium which was present as an impurity in all his salts. Because of this, he is sometimes described as the father of flame emission spectroscopy, though he did not identify the source of the line, or propose his experiment as a method of analysis. He also proposed that light rays of different colours travelled at different speeds to explain the action of a prism, and suggested that this could be verified if the moons of Jupiter appeared as slightly different colours at different stages of their orbit. An experiment by James Short failed to confirm his hypothesis. Melvill died in Geneva in 1753, aged 27.

Wet chemistry

Wet chemistry is a form of analytical chemistry that uses classical methods such as observation to analyze materials. It is called wet chemistry since most analyzing is done in the liquid phase. Wet chemistry is also called bench chemistry since many tests are performed at lab benches.

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