Starch-Iodine Clock (Hands-on)
A clear solution turns blue on its own.
Reference: “Chemical Demonstrations, Volume 4,” by Bassam Z. Shakhashiri, University of Wisconsin Press: Madison, 1992; p. 16.
“Chemical Demonstrations, Volume 1,” by Lee R. Summerlin and James L, Ealy, Jr., Second Edition, American Chemical Society: Washington, 1988; p. 107.
“Chemical Demonstrations, Volume 2,” by Lee R. Summerlin, Christie L. Borgford and Julie B. Ealy, Second Edition, American Chemical Society: Washington, 1988; p. 149.
Prepare Solution A:
Dissolve 4.3 g KIO3 in 1 L of water.
Prepare Solution B:
Make a paste of 4 g of soluble starch and a small amount of water.
Slowly add 500 ml of boiling water and cool.
Add 0.2 g Na2S2O5 and 5 ml of 1M H2SO4 and dilute to 1 L.
To make a 1M H2SO4 solution, dilute 55 ml of concentrated H2SO4 to 1L.
Pour 50 ml of solution A into a 250-ml beaker.
Place 50 ml of solution B into another beaker.
Pour solution B into solution A and swirl.
Explanation: The two solutions react to form an intermediate which is also consumed in the reaction until one a reactant is consumed. This intermediate, iodine, then forms a blue complex with the starch.
Tips:
Old Nassau Clock (Demo)
A clear solution turns orange then blue on its own.
Reference: “Chemical Demonstrations, Volume 4,” by Bassam Z. Shakhashiri, University of Wisconsin Press: Madison, 1992; p. 29.
“Chemical Demonstrations, Volume 1,” by Lee R. Summerlin and James L, Ealy, Jr., Second Edition, American Chemical Society: Washington, 1988; p. 109.
Prepare Solution A:
Make a paste of 4 g of soluble starch and a small amount of water.
Slowly add 500 ml of boiling water and cool.
Add 15 g NaHSO3 and dilute to 1 L.
Prepare Solution B:
Dissolve 3 g HgCl2 in 1 L of water. Avoid touching the HgCl2.
Prepare Solution C:
Dissolve 15 g KIO3 in 1 L of water.
Pour 50 ml of solutions A, B and C in three separate beakers.
Add A to B to C and swirl.
Explanation: Two reactants combine to form an orange solid, HgI2. Further reaction converts the iodide to iodine to form the iodine-starch complex.
Oscillating Colors (Demo)
A solution changes colors for several minutes.
Reference: “Chemical Demonstrations, Volume 2,” by Bassam Z. Shakhashiri, University of Wisconsin Press: Madison, 1985; p. 266.
Add 83 ml of concentrated sulfuric acid to 500 ml of water and dilute to 1 L.
Prepare Solution A:
Dissolve 19 g KBrO3 in 500 ml of the 1.5M H2SO4 just prepared.
Prepare Solution B: (This solution has a limited shelf-life.)
Dissolve 11 ml of ethylacetoacetate in 500 ml of water.
Prepare Solution C:
Dissolve 4.5 g Ce(NH4)2(NO3)6 in 500 ml of 1.5M H2SO4.
Prepare a Ferroin Solution:
Dissolve 0.23 g FeSO4·7H2O and 0.46 g 1,10-phenanthroline in 100 ml of water.
Pour solution A and solution B into a 2-L Florence flask.
Adjust the magnetic stirrer to produce a vortex in the solution.
Add 30 ml of the Ferroin solution.
Add solution C.
Explanation: A series of equilibria are shifting back and forth to produce the oscillating colors. The colors generally come from the iron and cerium complexes. The iron(II) complex is red and the iron(III) complex is blue. These can easily be seen when adding the ferroin solution. The cerium(III) complex is colorless and the cerium(V) complex is yellow. In the middle of the oscillations the colors should go from green to blue, to violet, to red and back to green.
Tips:
Color Wheel (Hands-on)
Students color a wheel for absorbance and reflection of light.
Reference: none
Give a handout that has a circle divided into six equal portions like a pie.
Label the six parts clockwise: red, orange, yellow, green, blue and violet.
Have the students color in the portions of the pie with the appropriate colors.
Using the wheel, discuss the wavelengths of light and absorption / reflection of colors.
Explanation: If something is red, it is reflecting red light and absorbing green light. These colors are opposite each other on the color wheel.
Tips: Relate to the primary colors: red, blue and yellow.
Lemonade (Demo)
Several different color solutions are made before lemonade results.
Reference: “Chemical Demonstrations, Volume 1,” by Lee R. Summerlin and James L, Ealy, Jr., Second Edition, American Chemical Society: Washington, 1988; p. 46.
Dissolve 30 g of FeCl3·6H2O in 100 ml of water.
Place 15 drops in beaker 1.
Dissolve 22 g of NH4SCN in 100 ml of water.
Place 2 drops in beaker 2 and 10 drops in beaker 3.
Prepare a saturated solution of tannic acid. (1 g tannic acid / 0.35 ml water)
Place 12 drops in beaker 4.
Prepare a saturated solution of oxalic acid. (1 g oxalic acid / 7 ml water)
Place 10 ml in beaker 5.
Pour water in a large beaker or pitcher.
Pour some water in beaker 1 and notice a pale yellow color.
Pour beaker 1 back into the large beaker.
Pour the solution in the large beaker into beaker 2 and notice an orange color.
Pour beaker 2 into the large beaker.
Repeat with the remaining beakers.
The color of beaker 3 will be red and beaker 4 will be black
After beaker 5, the color will be lemonade.
Explanation: The colors result from different concentrations and complexes of iron(III): chloride is light yellow, thiocyanate is red, tannate is black and oxalate is yellow.
Tips:
Two solutions are mixed together and light is given off.
Reference: “Chemical Demonstrations, Volume 1,” by Bassam Z. Shakhashiri, University of Wisconsin Press: Madison, 1983; p. 171.
Prepare Solution A: (This solution has a limited shelf-life.)
Dissolve 0.8 g of cysteine hydrochloride in 50 ml of water.
Prepare Solution B:
Dissolve 5 g of potassium hydroxide in 100 ml of water.
Add 0.3 g of luminol and swirl to dissolve.
Prepare Solution C:
Dissolve 0.25 g of CuSO4·5H2O in 100 ml of water.
Dilute 25 ml of this solution to 1 L.
Pour 1 ml of solution A and 5 ml of solution B into test tube 1.
Stopper and gently mix the solutions.
Pour 12 ml of solution C and 10 drops of 3% hydrogen peroxide into test tube 2.
Dim the lights and pour tube 1 into tube 2.
Quickly stopper the tube and shake.
Observe the light given off.
Explanation: The luminol reacts with the hydrogen peroxide and gives off light in the process.
Tips:
