Iron III Thiocyanate Ion Equilibria

A chemical equilibrium is set up so that with the addition of either reactant, a color change will be observed when the equilibrium shifts to favor either the products or reactants.

MATERIALS

-          3% ammonium thiocyanate solution in dropper bottle

-          1% iron III chloride solution in a dropper bottle

-          1% mercury II chloride solution in dropper bottle

-          2% sodium dihydrogen phosphate solution in dropper bottle

-          5 50mL beakers labeled A,B,C,D,E

-          100mL beaker

-          Squirt bottle with D.I. water

-          Stirring rod

-          Overhead projector

PRESENTATION

1.

-          Place the five beakers onto the overhead projector

-          Fill all of the beakers with about 10mL of D.I. water and wait a minute for the water to become still.

-          Carefully add 5 drops of 1% FeCL₃  into one side of beaker A and 5 drops of 3% NH₄SCN to the other side to show the both are colorless solutions

-          Stir the solution to serve as the color standard

2.

-          Add 5 drops of the solution from beaker A to beakers B,C,D, and E

-          Add 5 drops of 1% FeCl₃ to beaker B and stir (color will darken)

-          Add 5 drops of 3% NH₄SCN to beaker C and stir (color will darken)

-          Add 1 drop of NaH₂PO₄ to beaker D and stir (color will lighten)

-          Add 10 drops of HgCl₂ to beaker E and stir (color will lighten)

DISCUSSION

-          Le Chatelier’s principle

HAZARDS (MSDS Links)

Ammonium Thiocyanate:  http://www.sciencelab.com/msds.php?msdsId=9927080

Iron III Chloride:  https://www.sciencelab.com/msds.php?msdsId=9924033

Mercury II Chloride:  http://www.sciencelab.com/msds.php?msdsId=9924616

Sodium Dihydrogen Phosphate:  http://www.sciencelab.com/msds.php?msdsId=9925021

REFERENCES

Doris Kolb, “Introduction to Overhead Projector Demonstrations”, Journal of Chemical Education, 1987, 64, 348.

Lee R. Summerlin and James L. Ealy, Jr., “Chemical Demonstrations: A Sourcebook for Teachers”, The American Chemical Society, Washington, D.C., 1955