Using Flame Tests to Determine the Identity of Metal Cations

Introduction

Background topics should include:

  • Start by introducing Robert Bunsen, his invention the Bunsen burner and the story of how and why he used them for the first flame tests.
  • Explain what cations are and give a clear explanation of why metals form cations by losing electrons during bonding. Research and explain what a chemical salt is and why they are good for demonstrating flame tests.
  • Explain what is known about valence electrons and then relate valence electrons in ground state electron configuration to excited state electron configuration.
  • Further discuss what happens when electrons are excited (be sure to talk about their “fallback” to ground state from excited state.)
  • Research and discuss how electron excitation is related to firework production and/or other cool light phenomena.
  • Be sure to cite ALL above at least once per paragraph and there should be a minimum of 5 large, well developed paragraphs in your introduction PLUS the objective.

Possible resources:

Textbook is actually a good source too for some of this!

Objectives:

  • To determine the identities of unknown metal salts by exciting their valence electrons during flame tests.

*** There is no hypothesis for this one lab for a change – nothing substantial can be predicted before actually performing it.

Materials and Methods

Part I – Flame Tests for Known Metal Salts

1.Pre-soak many wooden splints for at least 24 hours in water.

2.Set up a 400 mL beaker of water at each station to be used to put out flames as needed during the activity.

3. At each station, set up and carefully light a Bunsen burner to have a focused, blue flame.

4. Dip the end of a soaked, wooden splint into each metal salt, and then wave carefully into Bunsen burner flame. Take a picture of each colored flame that is produced. (You may wish to also take a video of yourself saying the name since you can’t label it.)

5. Record observed color (be descriptive) and name of metal cation into Table 1 below.

6.Repeat steps 4 and 5 for each of the 7 salts with known metal cations.

7.Now repeat steps 4 and 5 for each of the 5 UNKNOWN metal cations (in salts) recording observations in Table #2.

8.Compare pictures and qualitative observations to determine the identity of these unknowns. Record these inferences into Table #2.

***Clean up according to teacher’s directions. Check ipads to make sure you have pictures of each flame (12 total pictures, CLEARLY labeled in some way by metal salt name or unknown #). If you are unsure of any or got a bad picture, ask teacher if you can repeat a test.

Results

Table 1 – Qualitative Observation of Known Metal Cations During Flame Tests

Metal CationFlame Color

Table 2 – Identifying the Unknown Metal Salts

Unknown # Flame ColorInferred Cation Identity

Figure #1 – Lithium ChlorideFigure #2 – Potassium Chloride

etc.

COLOR PHOTO GOES HERE!COLOR PHOTO GOES HERE!

*** Report must include 7 figures that are the photos taken of the known metal salts.

Figure #8 – Unknown #1Figure #2 – Unknown #2

Etc.

*** Report must also include 5 figures that are the photos taken of the unknown metal salts.

There are no calculations for this lab and there is no graph. However, the images requested above (12 total) in the format requested above are a huge part of this lab. It is suggested that you have between 6 and 8 images per page in two columns. They don’t need to be giant pictures nor should they be. If you don’t have a color printer at home, it is permitted to print a limited number of color copies in the Prep library. Be sure to finish your lab report early so that you can print in the library as needed. Recall that you can’t print from the ipad so you will have to save to your google drive and then open up on a school computer if need be. You can’t assume that will work the afternoon before or morning the report is due. There will surely be a tech issue and you will not get any extension. Be warned!!

***You may NOT append any tables or figures for this report. All must appear in proper order as one continuous report. Format is a large part of your grade even more so than usual this time.

Discussion

Some hints for what to discuss…

  • What was happening during the flame tests?? Explain in terms of valence electrons, ground state, excited state, cations, etc.
  • Why did different elements burn different colors?
  • Make some comparisons among the different results – which were most similar, most easily distinguished and why.
  • Make some inferences about the identifications that were made for the unknown. Which were easy? Difficult? Possible errors sources? Contamination? How? (It will be tempting to use pronouns here – don’t do it!! You can give your opinion and inferences without using “I” and “my”!
  • Was objective met? Successfully? How so?

References

Don’t forget References section and use my quick reference APA guide and/or the link on our class website.

*****Use the original guidelines!! Use the hints and reminders to do a check of your report before handing it in! This lab will not be worth a smaller amount of points than the typical labs, but will still be a substantial grade for this marking period.