Introduction: (Initial Observation)
While making a quick barbecue on the gas stove, I added a small amount of salt. Suddenly all the existing blue flames became yellow. I remembered that in another occasion I had seen flames turn green and I did not know why!
Now I was more curious. I started to test different materials to see their effect in the flame. I was wondering if we could just use the flame to identify different chemicals. It was easy to collect a few samples of pure chemicals such as Sodium Bicarbonate (Baking Soda), Calcium Chloride (Snow melter), Copper Sulfate (one of the pool supplies), and some others. I started to test them by putting a small amount of the substance on the tip of a metal spoon and exposed it to the flame.
The first few tests were rewarding. I noticed that everything with sodium will create the same yellow color. Now I knew that what really effects the color of the flame is the metal ion. In other words every time that I see that famous yellow in the flame, I immediately know that there is some sodium involved. The picture in the right shows the effect of a sodium salt in the flame of a Bunsen Burner.
Later I was able to get some barium salt and see its green flame color. Barium in the nature is in the form of Barium sulfate. Its mineral is called Barite. This metal is used as a “getter” in vacuum tubes. The most important Barium compounds are peroxide, chloride, sulfate, carbonate, nitrate, and chlorate. Lithopone, a pigment containing barium sulfate and zinc sulfide, has good covering power, and does not darken in the presence of sulfides. The sulfate, as permanent white, is also used in paint, in X-ray diagnostic work, and in glass making. Barite is extensively used as a weighing agent in oil wells drilling fluids, and is used in making rubber. The carbonate has been used as a rat poison, while the nitrate and chlorate give colors in pyrotechny. The impure sulfide phosphoresces after exposure to the light. All barium compounds that are water or acid soluble are poisonous. Naturally occurring barium is a mixture of seven stable isotopes. Twenty two other radioactive isotopes are known to exist.
Barium is in the group of Alkaline-earth metals. These metals are very reactive and can not be found in the nature in metalic form. The picture in the left shows the effect of a Barium salt in the flame of a Bunsen Burner.
The next substance that I tried was Potassium salt. Potassium is never found free in nature, but is obtained by electrolysis of the chloride or hydroxide, much in the same manner as prepared by Davy. It is one of the most reactive and electropositive of metals and, apart from lithium, it is the least dense known metal. It is soft and easily cut with a knife. It is silvery in appearance immediately after a fresh surface is exposed.
It oxidizes very rapidly in air and must be stored under argon or under a suitable mineral oil. As do all the other metals of the alkali group, it decomposes in water with the evolution of hydrogen. It usually catches fire during the reaction with water. Potassium and its salts impart a lilac color to flames.
Lithium is a member of Group 1 (IA) element called “alkali metals”. Lithium is a solid, only about half as dense as water. A freshly cut chunk of lithium is silvery, but tarnishes in a minute or so in air to give a gray surface.
The picture in the left shows the effect of a Lithium salt in the flame of a Bunsen Burner.
One of the most difficult things for beginners to comprehend in chemistry is the subject of “subatomic particles” (Neutron, Proton, Electron). We explore things that are so small and weigh so little that they are almost not there, yet their effects when in partnership with zillions of others fill our lives. These effects are the basis of CHEMISTRY, which is the interaction of electron orbitals. Your teacher probably has some Styrofoam, or gumdrop atoms or molecules around, and perhaps even has some atoms with some ‘electrons,’ and has been telling you that the electrons revolve around their nuclei just as the planets go around the sun.
When you keep a steel wire (such as a needle or paper clips) on the flame (experiment it in a dark place!) it will glow (fluoresce) in a brilliant yellow, red color. Heat will excite some electrons, especially in the outer layer of atoms, so they will jump to a higher orbit. The electrons then like to fall back into their original orbits. When that happens, a photon of visible light is emitted.
In an electric light bulb, an electric current creates heat. Light bulb filament that is usually made of a very tin tungsten wire, glows when it gets hot by electric currents.
Different metals have different number of orbits and different number of electrons in their outer layer. So the amount of energy that electrons need to get excited and jump to a higher level is not the same in all metals. As a result the amount of energy that they release when they fall back to their original orbit is not the same. So metals (and all other elements) create light, which are in different parts of the spectrum. Some are visible and some not.
Identifying elements (specially metals) by the visible light that they produce when heated is called flame photometry. There are complex devices in chemical laboratories called flame photometers that use this method to identify and measure the amount of certain metals in a solution. In medical labs these devices are used to measure the amount of sodium in blood. (Sodium in blood is in the form of Sodium Chloride).
Flame colors for other elements are as follows:
- To experiment with flame tests on different salts.
- To predict the identity of an unknown metal ion from a flame test.
Can we identify metals by the color of their flame when they burn? Can we identify metals in chemical compounds such as salts?
For example Sodium Chloride, Magnesium Chloride, Potassium Chloride are all White and look the same. Can we use flame color to identify and distinguish these three salts from each other?
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
The independent variable (also known as manipulated variable) is the type of metal or metallic salt we test.
The dependent variable (also known are responding variable) is the color of the flame that each metal or salt produces.
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.
My hypothesis is that some metal ions can be identified by the color of their flames, but some others may create radiations that are invisible to human eye so we will not see any change in the color of the flame.
Design an experiment to test different salts for the color of the flame they produce.
Take the necessary precautions before beginning this experiment. Wear safety goggles, apron and gloves.
Collect samples of metallic salts such as Sulfate, Chloride, Carbonate, Hydroxide or Nitrate of different metals. Put a small amount of the salt on tip of a platinum wire and expose it to the flame of a gas burner. You use a platinum wire because it does not change the color of flame by itself. If you don’t have access to a platinum wire, use a metal spoon, but you need to expose the sample to the flame in a way that the metallic spoon is not touched by the flame. Otherwise the spoon may also have some effect on the flame. Repeat the experiment for each and every metallic salt that you have gathered and record the results.
Platinum wire is relatively expensive and can be purchased from laboratory suppliers.
Make sure you don’t spill any of the chemicals on the gas burner itself. If this happens, you need to wash everything carefully to get your blue flame back.
You can do the flame test by spraying s solution on the flame. If your salt is water soluble, dissolve it in distilled water and spray it on a horizontal flame to see how does it change the flame color. You use a burner with horizontal flame so the spills can not get to the burner itself.
You may also spray the powder on the flame. Try it with table salt first to see how does it work.
Materials and Equipment:
1. Platinum wire, spatula, or spoon to hold the sample while exposing it to the flame.
2. Samples of Metallic Salts or metals.
Note: Metals such as Iron (nail), copper (pipe) and aluminum (sheet) are available form hardware stores. US pennies are zinc coated by copper. If you use a sand paper to remove copper from a penny, what remains is zinc. US nickel however has very little nickel. It’s mostly copper. Some Canadian coins are pure nickel. Nickel is attracted by a magnet. Use a magnet to determine if a coin is nickel or no.
Other metals are hard to get, that is why you use the salts of those metals. For example instead of sodium metal, you may use sodium chloride (table salt). Also instead of magnesium you may try magnesium sulfate (Epsom salt) available from supermarkets and pharmacies. Calcium carbonate is a good source of calcium in the form of lime stone, marble, sea shell and egg shell. Strontium compounds that produce red flame are more difficult to find. You may ask a local science supplier or MiniScience.com for a small sample of any Strontium salt.
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
In another experiment you can dissolve some metallic salt in distilled water and spray it into the flame. You should observe the same color effects.
In more advanced experiments in this subject, you may try to calculate the concentration of a metal ion, based on the brightness of the light that it produces.
Summary of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Most metals create a special color light when heated. We can use that color to identify the type of metal. When metals are pure, we may visually or based on physical properties such as color and density identify the type of metal. But when metals are in a compound, Flame Photometry can be a technique that positively identifies a metal.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.
References and Additional Information:
Spectroscopy is the analysis of light spectra and the way in which light interacts with matter. When light is analyzed, it is commonly separated into its component colors. The light source is directed on a slit and the “beam” of light is separated using a prism or grating.
The reason that the images are lines is that the light from the lamp is focused on a narrow slit. The illustration shows the separation of a light beam into its component colors.
This produces an image of the slit which has the shape of a line. The resulting beam of light can be broken into the color spectrum. or into its components of the spectrum emitted by the atom. You can see the specific colors emitted by the light source. A white light source will give a spectrum like the one shown above.
The emission spectrum for sodium shows only two colors in the visible color range. The two colors are yellow and have wavelengths of about 590 nm. The continuous spectrum and calibration scale is shown to give approximate wavelength values.
Street lights are sodium vapor lamps in many communities. These lamps have an orange yellow tint. You can see from the emission spectrum why the sodium vapor lamps would appear yellow and not white. These lamps consume less energy than the older blue colored mercury vapor lamps. Mercury vapor lamps have been sold in hardware stores for yard lighting.
Colorado State University physics department has an animation of the H atom at this URL
COLORED FIRES IN PYROTECHNY IS MADE BY THE FOLLOWING SALTS:
|Light Blue.||Aluminum Sulfate|
|Dark Blue||Copper Carbonate|
|Light Green||Barium Carbonate|
|Red.||Strontium Nitrate or Carbonate|
For more accurate identification of elements by their flame color, we do not rely on our eyes; instead, we use special equipment to determine the wavelength of each emission. We call it emission spectrum. Each emission spectrum has certain peaks. In other words it will have the most emission of certain wavelength lights. We use such wavelengths and such instruments for final determination of the metal or metals or even other elements in any substance. Metals usually have emissions in visible wavelengths. Nonmetals usually have emissions in invisible wavelengths. Following are two good links for understanding emission spectrum.
Description: Methanol solutions of several different metal salts are sprayed into a Bunsen burner. A ball of fire is produced that gives characteristic flame-test color.
Methanol is poisonous and flammable. This test needs a fire safe environment, protective clothing and must be performed by experienced adults.