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Flame Tests? Can you Really Identify an Element or a Compound by Putting it Into a Flame?

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Author: Dr. Muriel Gerhard

Grade Level: 7th - 8th; Type: Chemistry

Objective:

To determine whether it is possible to identify a compound by using a flame test.

Research Questions:

  • What is an element?
  • What is a compound?
  • What is an ion?
  • What is the Periodic Table of Elements? How is it used?
  • In the flame test, what happens to the metal ions that results in the emission of visible light?

On the information level, this experiment serves to acquaint students with basic procedure frequently used in chemistry, called a flame test which is used to detect the presence of specific metal ions. This process is based on our knowledge of each elements characteristic emission spectrum. For example, we know that when we heat calcium we get an orange flame, when we heat lead we get a blue flame, when swe heart sodium we get an intense yellow flame. In conducting the flame test, we simply take a sample of the substance, using a platinum wire and place it in a hot flame we then observe the color. A platinum or nichrome wire is used, formed into a loop to hold the substance being tested and then cleaned using dilutes hydrochloric acid. For example, copper will yield a blue flame, iron will give us a gold color and magnesium will yield a brilliant white. In industry, the flame test is very useful for the identification of polymers. It is also used in salt analysis.

This science fair experiment also serves to acquaint students with the essential processes of sciencing such as the importance of the use of a control, of identifying dependent and independent variables, of data collection, of pictorial and or graphic presentation of data and of being able to make better judgments as to the validity and reliability of their findings. They take on the role of scientists and in the process they learn to act as one.

Materials:

  • dilute hydrochloric acid
  • distilled water
  • 4 test tubes
  • Test tube
  • rack
  • 3 chloride test solutions ( sodium, potassium, calcium)
  • sodium fluoride
  • spark igniter
  • Bunsenburner
  • wire and holder
  • two small beakers

These materials may be obtained from the school laboratory or purchased from Chem. Scientific . Most middle and junior high schools have these materials in their labs.

Experimental Procedure:

  1. Gather all the materials that you need for this project. These include: dilute hydrochloric acid, distilled water, 4 test tubes, a test tube rack, 3 chloride test solutions (sodium, potassium’ calcium ),sodium fluoride solution, a spark igniter, a bunsen burner, a wire and holder, two small beakers, labels, a pen, safety glasses, an apron and gloves.
  2. Exercise care in handling all of the chemicals. Line up your test tubes in the test tube rack.
  3. Take out your labels and write out the names of each of the compounds you will be flame testing. These include sodium chloride, potassium chloride, calcium chloride and sodium fluoride. Paste them on each of the test tubes.
  4.  Make a copy of the chart provided below so that you can readily enter your observations as you conduct the flame test on each of the compounds.
  5.  Light the Bunsen burner. Regulate the flame. Take the wire, place it in the dilute HCL and then into the distilled water so that it is absolutely clean. Now test the wire to make certain it is clean by holding it with the wooden handle and placing it in the flame of the burner under it is red hot.
  6. Begin the tests, dip the clean wire into each of the test solutions, one at a time, now place the wire in the flame and observe the changes in color for each one of the solutions. Make certain to clean the wire after each trial. Record your observations in your data chart.
  7. Carefully clean up the remaining solutions and chemicals.
  8. Review your observations. What do you conclude? Write up your report. Make certain to include all of the research you completed in answering the questions under questions for background research. Include your bibliography as well as the practical applications of the flame test for chemical research.

                                      Chart for Recording Observations is provided below

      Compound Color of Flame
Calcium chloride  
Potassium chloride  
Sodium chloride  
Sodium fluoride  

 

Terms/Concepts: Elements, compounds, ions. Periodic Table of the Elements

References:

http://en.wikipedia.org/wiki/flame­_test

Masterton W,,Slowinski E, Walford E, Holt,Rinehart and Winston New York, 1980

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