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Flame Tests a new Look at an Old Favorite Teachers’ Notes


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Flame Tests

A New Look at an Old Favorite
Teachers’ Notes:

The purpose of this activity is to extend the student’s understanding of the phenomena of visible spectra produced by excited atoms. Students will be asked to determine the effect of pairing specific cations with different anions on the flame color. Students will also be asked to determine the effect of pairing two different cations on the color of the flame produced. This “guided inquiry” activity may be best suited for use in the classroom after the students have been introduced to the concept of visible atomic spectra and have observed some flame tests for specific cations.


Materials:

1. Saturated aqueous solutions of the following salts are diluted 1:1 with methyl or ethyl alcohol: Cu(NO3)2 Ni(NO3)2 CuSO4 NiCl2

Other metal salts may be added as needed.

Quantities to prepare are dependent on the size of the spray bottles used.




  1. These solutions are placed into individual labeled spray bottles. (One set per lab group)


Method

1. As with any experiment it is necessary to observe all necessary safety precautions. Students will be spraying alcoholic solutions into a flame. Care must be taken to avoid lab mishaps by “overly engaged” students.


2. It is suggested that you run this experiment prior to introducing it to your students.
Student Presentation of results:

It is helpful to have students analyze and criticize each other’s work. By asking each group to present their work, a forum for discussion is provided.


Follow Up Questions
Students should be encouraged to develop the idea that atomic spectrum for each element is a property of that specific element that is not altered by its environment. This includes the anion in the mixture or mixing with other cations.
This lab activity can also be done as a demonstration.
Extensions

Students can be encouraged to research the role of atomic spectra in the following areas:

The discovery of Helium

How can paint chips from cars identify the make and model?

How are Lead and Mercury levels in water determined?


Student Lab Activity
Flame Tests – A New Look at an Old Favorite
Purpose: The purpose of this activity is to observe the visible spectra of specific metal cations, develop a hypothesis about the effect of chemical environment on the spectra and to propose possible extended experiments for further study.
Background: You have previously observed the visible spectra of different metal cations using the flame tests. In today’s investigation, you will look at the effect of changing anions and mixing cations on the color of light produced. Careful observations are needed.
Safety: Goggles and aprons are required. All books and other flammable objects should be placed away from the testing area. All other lab safety precautions should be followed.
Materials:

Spray bottles containing 50/50 aqueous/alcoholic solutions of:



Cu(NO3)2 Ni(NO3)2 CuSO4 NiCl2
Bunsen burner
Procedure:
In a darkened room, light a Bunsen burner.
Spray a sample of Cu(NO3)2 into the flame, observe the color emitted and record.
Repeat this procedure with the other samples in the remaining spray bottles.
Simultaneous spray samples of Cu(NO3)2 and Ni(NO3)2 into the flame. Make close observations.
Repeat this procedure using all combinations of the two metal cations.
Clean up:
Wipe down the lab bench and wash your hands.
Post Lab:
Prepare a group presentation (white board or overhead transparency) containing the following:


  • Data Chart listing metal cations, anions, mixtures and observations.

  • Develop a hypothesis to account for your observations on the effect of chemical environment on the color of the visible spectra produced by a metal cation. What are the experimental variables in this experiment? Make sure you hypothesis considers these variables.

  • Suggest additional testing that could help to prove or disprove your hypothesis.

  • Present these results to the class.


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