Effects of Concentration & Temperature on Iodine Clock Reaction, Exercises of Analytical Chemistry

Download Effects of Concentration & Temperature on Iodine Clock Reaction and more Exercises Analytical Chemistry in PDF only on Docsity! REACTION RATES EXPERIMENT The Iodine Clock Reaction 11B It is very important for a chemist to understand the conditions that affect the rate of a chemical reaction. In chemical manufacturing processes, controlling the rate of a given reaction can make all the difference between an economical process and an uneconomical one. In the previous experiment (11A) you investigated the principle that the rate of a reaction is determined by several factors, namely: concentration of reactants, temperature, surface area of reactants (for a heterogeneous reaction), nature of reactants, and the presence of a catalyst. In this experiment, you will carry out a different reaction, but you will again investigate the effect of the concentration of reactants (in Part I) and the temperature (in Part II) on the reaction rate. This experiment involves a reaction that is sometimes called an iodine clock reaction. There are a number of different combinations of chemicals that give a reaction of this type. What happens, essentially, is that there are two different reactions: one in which iodine is produced (a slow reaction) and one in which the iodine produced in the first reaction is used up (a fast reaction). By carefully controlling the quantities of reactants, you can obtain a situation in which the reactant in the second reaction is used up first, allowing iodine to form at that point. At very low concentrations the iodine then combines with starch to suddenly give a deep blue-black color, at a time determined by the conditions used. Hence the term “iodine clock”. The time elapsed from when the solutions were first mixed together until the point when the blue-black color appears is measured, and from this time measurement the rate of the reaction can be determined. You will alter the conditions of concentrations of reactants in Part I and temperature in Part II in order to determine their effect on reaction rate. OBJECTIVES 1. to observe and record the effect of changing the concentration of a reactant on the rate of a reaction 2. to observe and record the effect of changing the temperature of a system on the rate of a reaction SUPPLIES Equipment test-tube rack 4 beakers (250 ml.) 2 beakers (100 ml.) electric kettle or hot plate 2 graduated cylinders (10 ml.) lab apron 8 test tubes (18 mm x 150 mm) safety goggles 2 dropping pipet stopwatch or other timing device Thermometer ice Chemical Reagents Solution A: 0.020M KIO3 (potassium iodate) Solution B: 0.0020M NaHSO3 (sodium bisulfite) (also containing 4 g of starch and 12 mL of 1M H2SO4/L) PROCEDURE Part 1: Effect of Concentration 1. Put on your lab apron and safety goggles 2. Obtain in separate 100 mL beakers about 60 mL of Solution A (0.020M KIO3) and 90 mL of Solution B (0.0020M NaHSO3 containing H2SO4 and starch) and label the beakers. 3. In a 10 mL graduated cylinder place 10.0 mL of Solution A, using a dropping pipet, to obtain the volume as accurately as possible. Transfer the solution to an 18 mm x 150 mm test tube in a rack. 4. In the same manner measure out 10 mL of Solution B and transfer it to another test tube. Use a different graduated cylinder and dropping pipet than for Solutin A and keep the same ones for each solution for subsequent parts of the procedure. 5. In order to measure the time needed for the reaction to occur you will need a watch or clock with a sweep second hand, or preferably a digital watch with a stopwatch function. One partner must record the time, while the other partner mixes the solutions. Mix the solutions in one of the two test tubes and record the time from the instant they first mix. 6. Very quickly pour the solution back and forth between the two test tubes three times to make sure they are thoroughly mixed, then wait for the completion of the reaction. 7. Record the time at the instant the deep blue-black color first appears. 8. In order to study the effect of changing the concentration of Solution A, half the class will be assigned the values of 9.0 mL, 7.0 mL, 5.0 mL, and 3.0 mL, and the other half the values of 8.0 mL, 6.0 mL, 4.0 mL, and 2.0 mL. In each instance, measure out the volume in the graduated cylinder and add enough water to make it up to the 10.0 mL mark. Then transfer each dilution of Solution A to a test tube and mix it with 10.0mL Solution B as before. For each, record the time taken for the color to appear in your copy of Table 1 in your notebook.