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Flame Test: Going Further (26 Favorites)

LAB in Observations, Inferences, Atomic Spectra, Activity Series, Emission Spectrum, Electromagnetic Spectrum, Emission Spectrum, Ions. Last updated February 5, 2020.


Summary

In this lab, students will investigate the colors produced when several mixtures of metallic ions are placed in a flame.

Grade Level

High School

NGSS Alignment

This activity will help prepare your students to meet the following scientific and engineering practices:

  • Scientific and Engineering Practices:
    • Analyzing and Interpreting Data

Objectives

By the end of this lesson, students should be able to

  • Determine whether flame tests can be used to establish the activity series of a list of metals.

Chemistry Topics

This lesson supports students’ understanding of:

  • Atomic structure
  • Atomic spectra
  • Activity series

Time

Teacher Preparation: 30 minutes

Lesson: 45 minutes

Materials

For each group:

  • The following solutions
    • 1.0-M NaCl
    • 1.0-M LiCl
    • 1.0-M KCl
    • 1.0-M SrCl2
    • 1.0-M BaCl2 – Note: Barium chloride is highly toxic. Do not ingest the salt or solution.
    • 1.0-M CaCl2
    • 1.0-M CuCl2
  • Wood splints
  • Forceps
  • Bunsen burner
  • Striker
  • 22 small test tubes
  • Test tube rack

Safety

  • Use caution around open flames.
  • Barium chloride is highly toxic. Do not ingest the salt or solution.
  • Always wear safety goggles when handling chemicals in the lab.
  • Always be aware of an open flame. Do not reach over it, tie back hair, and secure lose clothing.
  • Wash hands after handling materials used to prepare for or perform this experiment.

Teacher Notes

  • This lab would be best conducted after a flame test lab or demonstration with each individual solution has been tested, such as the one available here: https://teachchemistry.org/classroom-resources/flame-test-rainbow-demo.
  • As this lab depends on qualitative data (color), the exact concentration of the solutions is not important, just as long as it’s enough for the colors to come through in the flame.
  • To prepare 50 mL (you can scale up if you need more) of approximately 1.0 M for each solution, follow these instructions:
    • Label a small beaker with the name of each salt it will contain.
    • Add the solid metal salts to the beakers:
      • 12.2 grams of Barium Chloride (BaCl2*2H2O) - Note: Barium chloride is highly toxic. Do not ingest the salt or solution.
      • 5.5 grams of Calcium Chloride (CaCl2)
      • 8.5 grams of Copper Chloride (CuCl2*2H2O)
      • 2.1 grams of Lithium Chloride (LiCl)
      • 3.7 grams of Potassium Chloride (KCl)
      • 2.9 grams of Sodium Chloride (NaCl)
      • 7.9 grams of Strontium Chloride (SrCl2)
    • Add about 50 mL of deionized water to each beaker and stir with a clean stir rod.
  • Remind students that when they put the wet splints in the flame, the wood will begin to burn if they leave them in for too long. Remind them to take their data readings before this happens.
  • Have the student clean the test tubes carefully after the lab so that there is no cross contamination.
  • The activity series for metals is included at the end of this document.

For the Student

Lesson

Background

On a color wheel, red + yellow = orange and blue + yellow = green. In this lab, you will investigate whether this idea works when doing flame tests of metallic ions.

Purpose

Student will mix various metallic salts and then perform flame tests to determine if some dominant colors correspond to the reactivity of metals.

Safety

  • Use caution around open flames.
  • Barium chloride is highly toxic. Do not ingest the salt or solution.
  • Always wear safety goggles when handling chemicals in the lab.
  • Always be aware of an open flame. Do not reach over it, tie back hair, and secure loose clothing.
  • Wash hands after handling materials used to prepare for or perform this experiment.

Materials

  • The following solutions
    • 1.0-M NaCl
    • 1.0-M LiCl
    • 1.0-M KCl
    • 1.0-M SrCl2
    • 1.0-M BaCl2
    • 1.0-M CaCl2
    • 1.0-M CuCl2
  • Wood splints
  • Forceps
  • Bunsen burner
  • Striker
  • 22 small test tubes
  • Test tube rack

Procedure

  1. Place six small test tubes into a test tube rack.
  2. To all six of the test tubes add 10 drops of NaCl solution.
  3. To each of the test tubes holding the 10 drops of NaCl add:
    - 10 drops of LiCl to the first test tube and swirl to mix.
    - 10 drops of KCl to the second test tube and swirl to mix.
    - 10 drops of SrCl2 to the third test tube and swirl to mix.
    - 10 drops of BaCl2 to the fourth test tube and swirl to mix
    - 10 drops of CaCl2 to the fifth test tube and swirl to mix
    - 10 drops of CuCl2 to the sixth test tube and swirl to mix.

*Notice that these make up the first row in your results table.The remaining solutions will be mixed in a similar fashion according to the subsequent rows in the table.*

  1. Break three wood splints in half and place one of the pieces into each of the six test tubes. Allow them to soak in the solution.
  2. While the wood splints are soaking, five additional test tubes into the test tube rack and add 10 drops of LiCl to each of the five test tubes.
  3. Repeat steps 1 – 5 for the remaining rows of the table to test all combinations of solutions, starting with 10 drops of the solution in the next row in each test tube and adding 10 drops of the solution in each column to one of those test tubes, as before. (Use 1 less test tube for each subsequent row, since you don’t need to retest combinations you have already done in a previous row, X’d out in the table.)
  4. Add 10 drops of all seven solutions into the last test tube and swirl to mix. Place a wood splint into the test tube and allow it to soak up the solution.
  5. Using the forceps, test each of the mixtures by placing the wood splint into a Bunsen burner flame. Record the colors of the flame in the appropriate box in the results table. Make sure to put only the wet portion of the wood into the flame.
  6. Before doing the flame test on the solution holding all of the metallic salts, predict what color you think the flame will be and why. After making your prediction, perform the flame test by putting the wood splint into the fire. Record the color of the flame.
  7. When you have finished testing all of the solutions, dispose of the wood splints, pour any of the mixtures left in the test tube into the sink, rinsing with water, and wash the test tubes carefully.

Results/Observations

Record the flame color for each mixture in as much detail as possible in the appropriate box.


10 drops LiCl

10 drops KCl

10 drops SrCl2

10 drops BaCl2

10 drops CaCl2

10 drops CuCl2

10 drops NaCl








10 drops LiCl







10 drops KCl







10 drops SrCl2







10 drops BaCl2







10 drops CaCl2








Predict what color the mixture of all salts mixed together will be and provide an explanation for your prediction.

Actual flame color with 10 drops of all solutions



Analysis

  1. In your testing, did any one color seem more predominant that others?
  2. If a predominant color corresponds to higher reactivity, place the chemicals tested in order of reactivity. Check the activity series of metals and see if your order was correct.

1. ___________________________

2. ___________________________

3. ___________________________

4. ___________________________

5. ___________________________

6. ___________________________

7. ___________________________

  1. Now rank the chemicals tested in order of reactivity according to the activity series of metals provided by your teacher.

1. ___________________________

2. ___________________________

3. ___________________________

4. ___________________________

5. ___________________________

6. ___________________________

7. ___________________________

  1. According to these two lists, does the predominance of a flame test color provide an accurate way of ranking reactivity? Why or why not?
  2. Would flame testing be a good way to distinguish between mixtures of different chemicals? Explain.
  3. Compared to flame tests for individual chemicals rather than mixtures, did any of the chemicals change their characteristic flame color when they were mixed with other chemicals? Explain your answer.

Activity series for metals:

Lithium

Li --> Li+ + e

Potassium

K --> K+ + e

Barium

Ba --> Ba2+ + 2 e

Strontium

Sr --> Sr2+ + 2 e

Calcium

Ca --> Ca2+ + 2 e

Sodium

Na --> Na+ + e

Magnesium

Mg --> Mg2+ + 2 e

Aluminum

Al --> Al3+ + 3 e

Manganese

Mn --> Mn2+ + 2 e

Zinc

Zn --> Zn2+ + 2 e

Chromium

Cr --> Cr3+ + 3 e

Iron

Fe --> Fe2+ + 2 e

Cobalt

Co --> Co2+ + 2 e

Nickel

Ni --> Ni2+ + 2 e

Tin

Sn --> Sn2+ + 2 e

Lead

Pb --> Pb2+ + 2 e

Hydrogen

H2 --> 2 H+ + 2 e

Copper

Cu --> Cu2+ + 2 e

Silver

Ag --> Ag+ + e

Mercury

Hg --> Hg2+ + 2 e

Platinum

Pt --> Pt2+ + 2 e

Gold

Au --> Au3+ + 3 e