A flame test is an analytical procedure used in chemistry to detect the presence of certain elements, primarily metal ionsbased on each element's characteristic emission spectrum. The color of flames in general also depends on temperature; see flame color. 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 electrons, 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 atomic energy shells 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.
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.
The use of cotton swab  or melamine foam used in "eraser" cleaning sponges  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. 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. PerkinElmer or Shimadzu, can be operated in emission mode according to the instrument manuals.
Goldsilverplatinumpalladiumand 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.
From Wikipedia, the free encyclopedia. Journal of Chemical Education.The flame test is used to visually determine the identity of an unknown metal or metalloid ion based on the characteristic color the salt turns the flame of a Bunsen burner. The heat of the flame excites the electrons of the metals ions, causing them to emit visible light.
Every element has a signature emission spectrum that can be used to differentiate between one element and another. Classic Wire Loop Method First, you need a clean wire loop. Platinum or nickel-chromium loops are most common. They may be cleaned by dipping in hydrochloric or nitric acid, followed by rinsing with distilled or deionized water. Test the cleanliness of the loop by inserting it into a gas flame. If a burst of color is produced, the loop is not sufficiently clean.
The loop must be cleaned between tests. The clean loop is dipped in either a powder or solution of an ionic metal salt. The loop with sample is placed in the clear or blue part of the flame and the resulting color is observed.
Wooden Splint or Cotton Swab Method Wooden splints or cotton swabs offer an inexpensive alternative to wire loops. To use wooden splints, soak them overnight in distilled water. Pour out the water and rinse the splints with clean water, being careful to avoid contaminating the water with sodium as from sweat on your hands. Take a damp splint or cotton swab that has been moistened in water, dip it in the sample to be tested, and wave the splint or swab through the flame.
Do not hold the sample in the flame as this would cause the splint or swab to ignite. Use a new splint or swab for each test. The sample is identified by comparing the observed flame color against known values from a table or chart. Red Carmine to Magenta: Lithium compounds. Masked by barium or sodium. Scarlet or Crimson: Strontium compounds. Masked by barium. Red: Rubidium unfiltered flame Yellow-Red: Calcium compounds. Green Emerald: Copper compounds, other than halides.
Faint Green: Antimony and NH 4 compounds. Yellow-Green: Barium, manganese IImolybdenum. Blue Azure: Lead, selenium, bismuth, cesium, copper ICuCl 2 and other copper compounds moistened with hydrochloric acid, indium, lead.
Light Blue: Arsenic and some of its compounds. Greenish Blue: CuBr 2antimony. Purple Violet: Potassium compounds other than borates, phosphates, and silicates. Masked by sodium or lithium. Because of the limitation, the flame test might be used to rule out the identity of an element in a sample, rather than definitively identify it.
Other analytical procedures should be conducted in addition to this test. This table lists the expected colors for elements in the flame test. Obviously, the names of the colors are subjective, so the best way to learn to recognize close-colored elements is to test known solutions so you know what to expect.
Share Flipboard Email.There are several different tests to detect and identify the ions in compounds. It is important that the test for any ion is unique. The results of a test must let you determine which ion is present, rather than being uncertain about which ion it is.
Different metal ions produce different flame colours when they are heated strongly. This is the basis of flame tests. To carry out a flame test:. The table shows the flame test colours for six common metal ions.
A sample of an ionic compound produces an orange-red flame test colour. Identify the metal ion present. Flame tests for metal ions There are several different tests to detect and identify the ions in compounds. Flame tests Different metal ions produce different flame colours when they are heated strongly.
To carry out a flame test: dip a clean wire loop into a solid sample of the compound being tested put the loop into the edge of the blue flame from a Bunsen burner observe and record the flame colour produced Carrying out a flame test The table shows the flame test colours for six common metal ions. Reveal answer up. Each metal ion produces a different flame test colour.This page describes how to do a flame test for a range of metal ions, and briefly describes how the flame colour arises.
Flame tests are used to identify the presence of a relatively small number of metal ions in a compound. Not all metal ions give flame colours. For Group 1 compounds, flame tests are usually by far the easiest way of identifying which metal you have got. For other metals, there are usually other easy methods which are more reliable - but the flame test can give a useful hint as to where to look.
Clean a platinum or nichrome a nickel-chromium alloy wire by dipping it into concentrated hydrochloric acid and then holding it in a hot non-luminous Bunsen flame.
Repeat this until the wire doesn't produce any colour in the flame. You soon learn to ignore this. Platinum is much better to use, but is much, much more expensive. If you have a particularly dirty bit of nichrome wire, you can just chop the end off. You don't do that with platinum! Dilute hydrochloric acid can be used instead of concentrated acid for safety reasons, but doesn't always give such intense flame colours.
When the wire is clean, moisten it again with some of the acid and then dip it into a small amount of the solid you are testing so that some sticks to the wire. Place the wire back in the flame again. If the flame colour is weak, it is often worthwhile to dip the wire back in the acid again and put it back into the flame as if you were cleaning it. You often get a very short but intense flash of colour by doing that. The colours in the table are just a guide.
Almost everybody sees and describes colours differently. I have, for example, used the word "red" several times to describe colours which can be quite different from each other. Other people use words like "carmine" or "crimson" or "scarlet", but not everyone knows the differences between these words - particularly if their first language isn't English.
What do you do if you have a red flame colour for an unknown compound and don't know which of the various reds it is? Get samples of known lithium, strontium etc compounds and repeat the flame test, comparing the colours produced by one of the known compounds and the unknown compound side by side until you have a good match.
However, I have received a helpful email from a student who says: "At my school we did some flame testing experiments, and. I think it looks more violet than blue, but it sort of changes each time you do it. If you thought chemistry was clear-cut, you are sadly mistaken!
The flame in this video was produced by burning methanol contaminated with a caesium compound.Home Activities Flame tests.Group 1 flame tests
Different salts contain different metal ions charged particles. When solutions of these salts are heated in a Bunsen burner flame, they give off characteristic colours.
The different colours in these fireworks are caused by different metal ions. You can be an analytical chemist or forensic scientist in this activity. Download the pdf file all worksheets and notes :.
First make sure that you have a clean flame test wire. Do this by holding the metal loop in the hottest part of the Bunsen burner flame. If it is clean, there should be no change in the colour of the flame when the metal loop is put in it.
If it is not clean, clean it by dipping it into the concentrated acid provided, then holding the loop in the Bunsen burner flame. Repeat this cleaning until there is no more change in the colour of the flame.
The next job is to do your flame tests. Dip the flame test loop into one of the known test solutions, then hold the metal loop in the edge of the Bunsen burner flame.
Clean the flame test wire, then test another known test solution. Keep going until you have recorded the colour of all of the known solutions.
Get your results checked. Carry out flame tests on the unknown solutions. Compare the flame test colours so you can work out which metal ions are present in each unknown solution.
We investigate lithium, sodium, potassium, calcium and copper II salts. They give readily identifiable colours and are specified for GCSE courses. Solutions are safer to use than solids, although both work in flame tests.
The activity is most easily carried out using different stations, one for each solution and with labelled flame test loops. This avoids the need to clean the flame test loops, and is desirable if adequate supervision of the students cannot be obtained.
If required, the flame test wires can be cleaned between each test by dipping in hydrochloric acid and heating. Sodium ions in particular are difficult to remove, and students will end up thinking everything contains sodium or makes a yellow flame! The expected colours are shown in the table below. Wear eye protection. At a concentration of 0. Note that 0. All Rights Reserved. What's it all about? Your browser doesn't support the HTML5 video tag. Student notes Teacher notes Technician notes Download the pdf file all worksheets and notes :.
Cleaning the wire First make sure that you have a clean flame test wire. Observing flame colours The next job is to do your flame tests. Identifying metal ions Carry out flame tests on the unknown solutions.
Teacher notes We investigate lithium, sodium, potassium, calcium and copper II salts. Salt solutions At a concentration of 0.Irja was our travel friendly to do business with. Words are unable to do justice to the warmth we received while Nordic Visitor is a great tour agency. We first contacted them, Alexandria listened to what we wanted to do and arranged exactly what we wanted for our trip.
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How to Do Flame Tests for Qualitative Analysis
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