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Color Changing ChemistryHave the students design and carry out their own investigation into a factor affecting the rate of a reaction. Materials? distilled water [deionized] ? 1000 mg vitamin C tablets [NOT-CHEWABLE]?tincture of iodine 2% solution [ made with alcohol]can substitute Lugol’s iodine [ 1.3 g iodine I2 + 2 g potassium iodide KI + 100 ml water]? Hydrogen peroxide H2O2 3% ?liquid laundry starch or spray starch [if using spray starch spray into 300 ml water for about 20 seconds, test a drop with iodine, making sure you get a strong positive reaction for starch, blue-black colour](Can also use ? tsp corn starch per each reaction, may slow down reaction time)? Thermometers? Small plastic cups (4 per student group)Activity procedure? make solution A: 5 ml vitamin stock solution + 2 ml of iodine solution + 30 ml water in a 100/200 ml beaker- the solution should be clear, if not add more Vitamin C stock- the web site says 5 ml of iodine but I found that it was too much and the solution had an iodine color? make solution B: 15 ml hydrogen peroxide + 2 ml starch solution + 30 ml water in a 100/200 ml beaker?Pour solution A into solution B then both back into the A beaker? Record time for changeMore Info: to make before activity? make vitamin C stock solution - crush 1 tablet and dissolve in 60 ml water? make starch solution 1] spray starch into 300 ml water for 20 seconds - test a drop - if not dark blue/black- spray some more - repeat test or 2] use straight liquid laundry starch?iodine solution 1] tincture of iodine use from bottle. It seems a little pricey. If you can get some Lugol’s might save some money or 2] Lugol’s iodine 1.3 g iodine I2 + 2 g potassium iodide KI + 100 ml waterYou might have to scale these up depending on your class size and the nature of their activities.Demonstrate the Iodine Clock Reaction for the students (Activity Procedure). Have the solutions prepared ahead of time, but make sure to carefully explain what is in each solution as you demonstrate. Write the proportions and temperatures of the solutions on the board.After the reaction occurs, have the class brainstorm variables in the experiment that they could change to make the reaction happen faster.Make groups of 2-4 students. Challenge the students to make the reaction happen in 90 seconds or less. Discuss proper experiment procedure: change 1 variable (temperature, solution, etc…) at a time and record how it changes). Give them 15 minutes to work. Note: They can change the water temperature as it comes out of the sink (they may not be able to measure degrees, but they can use hot, warm, lukewarm or cold water).At the end of their research phase, have the students set up their solutions in the way that they believe will create the fastest reaction. Celebrate the fastest reactions!Discuss the scientific process and its applications to their research and the real world.NOTES: By adjusting either the temperature or the concentration students should be able to develop methods to control the rate of the reaction.Temperature: Students should work within a 0?C to 40?C range. This makes it safe for classroom use. In addition the iodine starch complex which give the color change tends to breakdown above 40?C, thus there would be not be a color change.Concentration: Students should work by increasing or decreasing the water concentration thus concentrating or diluting the reactants. They might want to adjust the reactants directly. Discourage this as they will then have to keep the proportions of the reactants equal and might result in mistakes.Using increments of 10 ml seems to work well, but any uniform increase or decrease in amount of water should give acceptable results.? Note: You can use a colorimeter here to detect the change. You will not miss the change and the students get to use and hopefully understand the advantages of using technology. [see additional notes below]This activity was adapted from the Journal of Chemical Education, Jan 2002, vol 79, #1, p41-43. ................
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