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Flame Test Lab

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Flame Test Lab

Your company has been contracted by Julius and Annette Benetti. They are worried about some abandoned, rusted barrels of chemicals that their daughter found while playing in the vacant lot behind their home. The barrels have begun to leak a colored liquid that flows through their property before emptying into a local sewer. The Benettis want your company to identify the compound in the liquid. Earlier work indicates that it is a dissolved metal compound. Many metals, such as lead, have been determined to be hazardous to our health. Many compounds of these metals are often soluble in water and therefore easily absorbed into the body.

Electrons in atoms jump from their ground state to excited states by absorbing energy. Eventually, these electrons fall back to their ground state, re-emitting the absorbed energy in the form of light. Because each atom has a unique structure and arrangement of electrons, each atom emits a unique spectrum of light. The characteristic light is the basis for the chemical test known as a flame test. In this test, the atoms are excited by being placed within a flame. As they re-emit the absorbed energy in the form of light, the color of the flame changes. For most metals, these changes are easily visible. However, even the presence of a tiny speck of another substance can interfere with the identification of the true color of a particular atom.

To determine what metal is contained in the barrels behind the Benettis’s house, you must first perform flame tests with a variety of standard aqueous solutions or crystals of different metal compounds. These compounds are actually classified as salts (ionic compounds containing metals and non-metals chemically bonded). Then you will perform a flame test with the unknown sample for the site to see if it matches any of the solutions or salts you used as standard. Be sure to keep your equipment very clean and perform multiple trials to check your work.

Objectives

This laboratory has five objectives:

•identify a set of flame-test standards for selected metal ions •relate the colors of the flame test to the behavior of the excited electrons in a metal ion •draw conclusions and identify an unknown metal ion by using a flame test •Demonstrate proficiency in performing a flame test

•Evaluate the usefulness of this method of metal identification •Explain how electrons absorb and release energy when they change energy levels

Equipment

Chemical safety goggles Q-TipsLaboratory burner Distilled water Unknown Sample
various salts

Procedure

1.Light the burner and adjust it so that the flame is almost colorless and about 2-3 inches in height showing a bright blue inner core. 2.Dip the Q-tip into metal chloride #1 and then hold the Q-tip in the flame. View the color change in the flame and note it in the data table. Repeat if necessary. 3.Repeat the procedure for the sample, but this time look through the diffraction glasses and see if you can detect any other colors. 4.Repeat step 3 for each of the other standard crystals or solutions. Record your observations in the data table. 5.Follow the procedure to test the unknown sample. Record your observations. (Remember: You are trying to identify the unknown. You may need to repeat some of the standards or the unknown to get the correct identification based on flame color). 6.Clean all apparatus and the lab bench.

Analysis Questions

1.Which metals produce similar flame colors (according to your naked eye)?

NaCl and NaNo3 both turned the color orange.

2.What metal ions are in the unknown solutions A and B from the barrels on the vacant lot? Clearly, and in detail, explain your reasoning.

The metal ions BsCl and LiCl are in the unknown solutions A and B from the barrels on the vacant lot.

3.A student performed flame tests on several unknown substances and observed that all of the flame colors were shades of red. What could the student do to correctly identify these substances?

The student could match their observances to the specific color a flame would make when it comes into contact with a substance.

4.During a flood, the labels from three bottles of chemicals were lost. The three unlabeled bottles of white solids were known to contain the following substances: strontium nitrate, ammonium carbonate, and potassium sulfate. Explain in great detail how you could easily test the substances and re-label the three bottles. (Hint: Ammonium ions do not provide a distinctive flame color).

To easily test the substances and re-label the three bottles you could create a flame with the substances and use diffraction glasses to find the substance’s color.

5.A reddish brown rock was held in a very hot burner flame. The flame appeared emerald green in color. What metal was most likely present in the rock?

BaCl was most likely present in the rock.

6.How would you characterize the flame test with respect to its sensitivity? Give a reason why the flame test is sometimes invalid.

The flame test could possibly read invalid if there is still a trace of the previous substance still in the burner or if there is a trace of the substance in the current substance that is being tested.

7.Based on your results and observations would this method be practical to determine the metals in a mixture? If not, why not. Explain your answer.

Based on my results and observations this method would not be practical to determine the metals in a mixture because you wouldn’t know which color is for which substance in the mixture.

8.Using the information learned about what color would you predict that copper nitrate would burn? Explain your answer. I think copper nitrate would burn at a blue/green color, because during the flame test copper burned at a blue/green color.

9. Some stores sell “fireplace crystals.” When sprinkled on a log, these crystals make the flames red, green, and violet. Explain how these crystals can change the flame’s color. What ingredients do you expect them to contain?

These crystals can change the flame’s color because they contain different substances that burn at different colors. I expect the ingredients in them are Barium and Strontium.

10. Using the rules you have learned on orbital filling diagrams; correctly fill in the following diagrams for Potassium (K) and Strontium (Sr). Correctly write the electron configurations under each diagram.

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