Jessica Blindt

Night Into Sunrise

Concept: A chemical reaction between an acidic solution and a basic solution causes a color change.

Materials:

1. two - 400 mL beakers

2. 600 mL beaker

3. 15-17 drops phenolphpthlalein

4. 2 spatulas full ferric ammonium sulfate

5. 30 mL sodium silicate solution

6. 2 spatulas full potassium ferrocyanide (This is not the poisonous variety.

7. 440 mL water

Directions:

Fill the two - 400 mL beakers halfway with water (200 mL each).
Beaker A: Add 20 drops phenolphthalein to beaker A.

Beaker B: Add 2 spatulas full ferric ammonium sulfate and 2 spatulas full sodium ferrocyanide to beaker B and stir (should produce blue/green color).

Beaker C: In the 600 mL beaker, add 40 mL water and 30 mL sodium silicate solution and stir. Pour beakers A and B at the same time into the 600 mL beaker C. The blue and colorless mix to become red. If it is yellowish, add more phenolphthalein to beaker A at the beginning.

Introduction: Has anyone ever stayed up all night? I did last week, and besides being very tired, I saw the sunrise. At first, it was very dark (hold up beaker B). But then the sun comes up and...(pour A and B into large beaker).

Explanation: A chemical reaction between an acid and a base has occurred here. Beaker A has phenolphthalein in it, which is something called an indicator. An indicator tells us whether we have an acid or base. The phenolphthalein is colorless in acid and pink/red in a base. Beaker A is colorless so this indicates an acid is present. Beaker B is blue because it contains an iron complex, which is basic. The beaker C has hydroxide ions in it, which are also basic which is present from the sodium silicate.

When I poured A and B into the large beaker, two things happened. The final solution turned pink/red because the phenolphthalein from beaker A turns pink in a base of hydroxide ions in Beaker C. The second reaction is that the blue iron complex of beaker B disappeared. This is because the third beaker had sodium silicate solution which reacted with the blue iron complex, changing it into a colorless iron silicate complex. The formulas for theses reactions are quite complicated and are not given here.

Safety: Take the usual precautions in handling chemicals.

Waste Disposal: Pour all materials down the sink and rinse beakers thoroughly.

Reference: Original Unknown

Alternate source: Summerlin, L, Borgford, C, Ealy, J, Chemical Demonstrations, Vol. 2, American Chemical Socitey, 1987, p. 129 Uses Strontium chloride to make red and white precipitates.