![]() ![]() ![]() The vitamin C tables are not standardized are pure ascorbic acid available in a real laboratory.Report Sheet Part A: Calculating the Rate of Vitamin C Oxidation using Initial Rate Method Record the time taken to see the blue color in each experiment. Remember to keep the amount of all other ingredients the same in all the repetitions for preparing solutions A and B. Repeat the above procedure with various amounts of Vitamin C in making solution A, 600 mg (0.6g) in the third sample, 800 mg (0.8 g) in the fourth, and 1000 mg (1.0 g) in the 5th. Record the time take to see the blue color after mixing A and B. Keep the measurement of all other reagents the same as in sample 1. Repeat the above procedure, but with 400 mg (0.4g) Vitamin C in Solution A. The total volume of the solution is 62 ml. ![]() Mix solutions A and B and start the stop-watch immediately to measure the time taken for the appearance of the signature blue color. Solution A: Dissolve 200 mg ( 0.2g) of Vitamin C powder in 25 ml of water in a beaker or a clear cup, and then add 6 ml 2% tincture iodine solution: Solution B: Dissolve a pinch of starch in 15 ml 3% Hydrogen peroxide, add another 16 ml water to this. That means prepare one set of A and B solution as shown in the video, mix and measure the time time taken for the appearance of the blue color using a stopwatch. Even though we are doing five samples with different amounts of Vitamin C, we will do one at a time.Part A: Calculating the Rate of Vitamin C Oxidation using Initial Rate Method This video is meant only for a demonstration purpose. We will be using a different amounts of reagents for our reactions. The concentration calculations in molarity is more of an estimation as we are not using standard pure chemicals. Watch the following video to see the set-up on iodine clock reaction at home using household items. Use a graph sheet or excel spread sheet to manipulate the data to find the rate law (zero, first, second, or?). The mols of Vitamin C taken in each sample, and the corresponding time are used to calculate the initial rate of the reaction. Use a stopwatch (cellphone) to measure the time taken for the appearance of blue color in each case and are recorded. That is why this reaction is known as the iodine-clock reaction.Ī set of four to five reactions will be set up with increasing amount of Vitamin C, keeping the amount all other reagents the same. Therefore, the rate of the Vitamin C oxidation can be followed by the time taken for the appearance of the blue free iodine-starch complex. If you have more Vitamin C, it will take more time for the completion, and the appearance of blue colored is delayed. This is an indication of the completion of vitamin C oxidation. Once the vitamin C is oxidized completely, the free iodine will be available, and it will complex with starch to give the blue color. So, there will not be any free iodine to complex with starch to give the blue color. If there is vitamin C, it will react with I 2. Free iodine in the presence of starch makes an I 2-Starch complex that is dark blue in color. Iodine (I 2) solution is a brown solution and dissolved Iodide (I -) ions are colorless. The following equation shows the 1:1 reaction between Vitamin C (Ascorbic acid) and Iodine.Ĭ 6H 8O 6 + I 2 à C 6H 6O 6 + 2I - + 2H + However, in kinetics lab experiments, this reaction is often used as an example where the speed of a reaction is measured or rather calculated. Since iodine is involved, and these are redox reactions not neutralization reactions, these titrations are called iodometric titrations. This we will see in the titration lab experiment. This reaction is often used in volumetry to quantify the amount of Vitamin C in a sample. Vitamin C (Ascorbic acid C 6H 8O 6 ) is oxidized by free iodine molecule as follows. ![]()
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