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Complex Ions Lab

Michael Morgan's picture
Wed, 03/19/2014 - 13:43 -- Michael Morgan
preview complex ions lab

This laboratory exercise accompanies the article "A guided group inquiry lesson on coordination compounds and complex ions". The laboratory serves as part of an extended exercise on the chemistry topic of coordination compounds and complex ions. The entire lesson also exposes students to how chemical research is conducted and the conflicts and uncertainties that lead to new theories and discoveries.

Concepts: 

coordination compounds, first year undergraduate/general, collaboration/cooperative learning

Time required: 

Five class periods for entire lesson.

Materials: 
  • Bonding and the Werner/Jorgensen Controversy
  • 1M NaOH
  • 1M HCl
  • concentrated ammonia
  • 1M CuSO4
  • dropper
  • several test tubes
Background: 

See article "A guided group inquiry lesson: Coordination compounds and complex ions" by Michael Morgan for the background about this activity.

Procedure: 
  1. Observe the peacock blue solution of copper (II) sulfate. The pretty blue color is due to the complex ion, tetraquacopper (II) ion. Write the formula:

     

    The solution could also be called tetraquacopper (II) sulfate because there is a sulfate ion present. The sulfate ion is not part of the complex ion.

  2. Place about a “finger’s worth” of the blue solution in the bottom of a test tube. Add a few drops of 1 M NaOH. Mix and write your observations:

     

    Now think of this as an AP predicting reactions problem.

    Solutions of sodium hydroxide and copper (II) sulfate are mixed

  3. Add some concentrated ammonia solution to the copper (II) hydroxide suspension in the tube. Keep your nose away from the fumes! The deep blue (indigo) color comes from the tetraamminecopper(II) ion. Write the formula for the complex ion:

     

  4. Keep adding and mixing the ammonia solution until all of the pale blue precipitate has become deep blue. Is the deep blue substance a precipitate?

     

    Concentrated ammonia solution is added to a suspension of freshly precipitated copper(II) hydroxide.

  5. Remove some of the deep blue solution (in to another test tube) until you have about one finger’s worth.
  6. Add a few drops of 1 M Hydrochloric acid solution now to the mixture.
  7. Observe the color where the acid mixes with the deep blue solution. What do you see?

     

  8. Mix and add acid until the entire solution is pale blue.
  9. Ammonia is a proton acceptor (Lewis Base). Write the equation for what happens to the ammonia:

     

  10. Will this new ion be attracted to the Cu2+ ions?

     

  11. What is the pale blue color due to?

     

    A solution of dilute hydrochloric aid is added to a solution of tetramminecopper(II) hydroxide. 

  12. Finally add enough HCl solution until the blue solid begins to disappear.

    A solution of hydrochloric acid is added to a suspension of copper(II) hydroxide. 

  13. Check for where to put the waste products for this experiment.
  14. Before leaving the laboratory, wash your hands thoroughly with soap and water.
Questions: 

Prelab Questions

  1. If you have a positive ion in solution what else must you have?
  2. What is a complex ion?
  3. What is a ligand?
  4. What is a counter ion?

Post Lab Question

At first you can add a little hydroxide ion to a copper (II) solution and it forms a precipitate. Then as you add more the precipitate dissolves. What is happening?

Preparation: 

Prepare:

  • 1 M CuSO4 
  • 1M NaOH
  • concentrated ammonia
  • 1M HCl
Credits: 
The author gratefully acknowledges the assistance of Daniel Rabinovich of UNCC with the graphics for this article. A Bonding Theory/ The Werner-Jorgensen Controversy, A Review of a two part simulation: http://pubs.acs.org/doi/pdfplus/10.1021/ed070p902.1
Attribution: 

Michael A. MorganFrancisco Bravo Medical Magnet High School, 1200 North Cornwell Street, Los Angeles, CA 90033

Student Document: 
Chemistry Domain: 
Chemistry Topic: