Purpose
To illustrate a time delayed reaction which leads to the exploration of several factors which effect reaction rate.
Materials
- Soluble starch
- Potassium iodate, KIO3
- Sodium hydrogen sulfite (sodium bisulfite), NaHSO3
- Sulfuric acid, H2SO4 (1.0 M)
- 2 ea. 1L Erlenmeyer flask
- 2 ea. 400 mL
- 1 ea. 25 mL and 100 mL graduated cylinder
- Stirring rod
- electronic balance
- optional -
- Read the MSDS/WHMIS sheets for all chemicals before using them
- Wear safety glasses
Procedure
- Prepare Solution A in a 1 L Erlenmeyer flask (Flask A) containing 0.9 L of water.
- Add 2 g of potassium iodate to flask A. Stir.
- Add distilled water to Flask A to make a total volume of 1 L.
- Prepare Solution B in a 1 L Erlenmeyer flask (Flask B) containing 0.9 L of boiling water.
- While stirring slowly add 4.0 g of soluble starch to Flask B.
- Add 0.8 g of sodium bisulfite to Flask B. Stir.
- Add 10.0 mL of 1.0 M sulfuric acid to Flask B. Stir.
- Add distilled water to Flask B to make a total volume of 1 L.
- Allow flask B to return to room temperature.
- Pour 100 mL of solution A in a 400 mL beaker (beaker A).
- Pour 100 mL of solution B in a second 400 mL beaker (beaker B).
- Pour the solution in beaker B into beaker A (and mix).
- Start the timer (optional).
Results
Upon mixing the two reactants the resulting solution turns dark blue after a set amount of time.
Follow-up Teaching Notes
- Time the reaction just prior to the demonstration so you can say a “magic word” to activate the reaction.
- Prepare the solution no earlier than the day before.
Connections
Rates of reaction.
Extensions
- Allow students to investigate the affect of concentration on rate of reaction by diluting a known amount of solution B with a known amount of water.
- Allow students to investigate the affect of temperature on rate of reaction by heating and cooling the contents of beaker A and beaker B.
Disposal/Clean-up
The solutions can be disposed of down the drain (Consult local regulations before any disposal activity).
