Date Completed: Lab Partner(s):

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1 Name: Lab Partner(s): Date Completed: Lab # 23: Factors Affecting Reaction Rate Accelerated Chemistry 1 Purpose Did you ever wonder why certain chemicals when mixed do not react; yet others upon immediate contact react violently? Some chemical reactions occur slowly under certain conditions, yet occur rapidly when conditions are changed. The time it takes for a chemical reaction to reach completion, or to reach equilibrium, is called the reaction rate. Reaction rate is important in practical industrial processes; consider the decomposition of sodium azide to produce N 2 (g) which fills the air bag in your car during a crash. If this reaction did not occur rapidly the bag would not inflate in time to protect your face and upper body. Also, consider the importance of reaction rate when synthesizing pharmaceuticals. If the reaction of salicylic acid with sodium acetate to produce aspirin did not occur in a timely manner, then it would be impossible to mass-produce this pain reliever. In addition if the reactant salicylic acid could not be made in a timely fashion, this subsequent reaction would be made impossible. In this lab you will be working for Giammanco Pharmaceuticals synthesizing an I - 3 /starch complex from potassium iodide, hydrochloric acid, and starch. This complex is a necessary precursor in the synthesis of a larger molecule being tested as a new drug for the treatment of Alzheimer s. The purpose of this lab is for you to ascertain how reaction conditions affect the rate at which the synthesis occurs. You will be specifically varying conditions such as: reactant concentration, reactant surface area, reaction temperature and the use of a catalyst. Your goal is to optimize the synthesis so it occurs in the shortest amount of time possible to allow the drug to be mass-produced. This is a large project. Different groups within the company will be working to analyze each variable and data will be shared between groups. You will also be trying to conserve materials, so your analysis will be done on a microscale. The initial calibration of the reaction time will be done and agreed upon by all groups before any trials are completed. OBJECTIVES 1. Identify how long it takes for the iodine reaction to go to completion using a set amount and concentration of reactants. 2. To determine the effect that a change in temperature, concentration and surface area has on the reaction rate. 3. Determine the affect that a catalyst will have on the reaction rate. 4. Explain on a molecular level why the reaction rate changes. PRELAB PROCEDURE 1: Calibration 1. Orient your well plate so that it is 4 wells down by 6 across. 2. Place 8 drops of KI solution in the top left well. 3. Add 2 drops of HCl solution to the KI in the well. 4. Add 4 drop of sodium thiosulfate to the mixture in the same well. 5. Add 4 drops of starch solution to the mixture. 6. Swirl the mixture by moving the well plate in small circles on the table. 7. Using the glass pipet and dispenser, add 0.4 ml of 3% H 2 O 2 to the same well. Begin timing immediately after the addition of the H 2 O 2 to the well. AccelLab23-RxnRates 1

2 8. Swirl the solution and monitor the color. Record the time it takes for the entire solution to turn 9. If the solution took more than approximately 20 seconds to turn the dark blue/black color, repeat steps 1-8 in a different well reducing the number of drops of sodium thiosulfate by one. Continue repeating trials until it takes approximately 20 seconds to obtain the color change. 10. If the solution took less than approximately 20 seconds to turn the dark blue/black color, repeat steps 1-8 in a different well increasing the number of drops of sodium thiosulfate by two. Continue repeating trials until it takes approximately 20 seconds to obtain the color change. 11. If the solution took approximately 20 seconds to turn the dark blue/black color, no additional trials are needed. 12. Record the number of drops of sodium thiosulfate solution used to achieve the 20-second time period. This number of drops will be used in all subsequent experiments. PROCEDURE 2: Concentration Affects 1. In the left well of the next empty row place 8 drops of KI solution. 2. Add 2 drops of HCl solution to the KI in the well. 3. Add the number of drops of sodium thiosulfate determined in Procedure Add 4 drops of starch solution to the mixture. 5. Swirl the mixture by moving the well plate in small circles on the table. 6. Using the glass pipet and dispenser, add 0.4 ml of 3% H 2 O 2 to the same well. Begin timing immediately after the addition of the H 2 O 2 to the well. 7. Swirl the solution and monitor the color. Record the time it takes for the entire solution to turn 8. Repeat steps 1-7 using 6 drops of KI solution and 2 drops of DI water in place of 8 drops of KI. 9. Repeat steps 1-7 using 4 drops of KI solution and 4 drops of DI water in place of 8 drops of KI. 10. Repeat steps 1-7 using 2 drops of KI solution and 6 drops of DI water in place of 8 drops of KI. PROCEDURE 3: Temperature Affects 1. Prepare 3 water baths as follows: a. Room temperature water bath by placing room temperature water in a 100-mL beaker. b. Hot water bath by placing a 100-mL beaker filled with 80 ml of water on a hot plate. Bring the water to a slow boil. c. Cold water bath by filling a 100-mL beaker half full with ice then adding water. 2. Record the temperature of each sample of water in the data table once the temperature remains constant. 3. Add 8 drops of KI solution to each of three small test tubes. 4. Add 2 drops of HCl solution to the KI in each of the test tubes. 5. Add the number of drops of sodium thiosulfate determined in Procedure 1 to each test tube. 6. Add 4 drops of starch solution to the mixture in each test tube. 7. Swirl the mixtures. 8. Using a glass pipet and dispenser, place 0.4 ml of 3% H 2 O 2 in three empty test tubes. 9. Place a test tube containing the reaction mixture and a test tube containing the H 2 O 2 into the room temperature water bath. Place a test tube containing the reaction mixture and a test tube containing the H 2 O 2 into the cold water bath. Repeat for the hot water bath as well. 10. Allow the solutions to remain in the water baths for 3 minutes to ensure thermal equilibrium is reached. 11. Add the reaction solution at room temperature to the test tube containing the H 2 O 2 at room temperature and swirl. 12. Begin timing immediately after the addition of reaction mixture to the H 2 O Record the time it takes for the entire solution to turn AccelLab23-RxnRates 2

3 14. Repeat steps for the cold water and hot water baths. PROCEDURE 4: Surface Area 1. Add 4 drops of HCl solution to each of two test tubes. 2. Add 5 drops of starch solution to the mixture in each test tube. 3. Add 3 ml of sodium thiosulfate solution to each test tube. 4. Add 0.8 ml of H 2 O 2 to each test tube. 5. Swirl the solution in each test tube. 6. Place 0.02 g of powdered KI crystals into an empty test tube. Mark it as P using a marker. 7. Place 0.02 g of KI crystals into an empty test tube. Mark it as C. 8. Pour one of the reaction mixtures into test tube C. Do not swirl. 9. As the mixture is added begin timing. Record the time it takes for the entire solution to turn a dark blue/black. 10. Repeat steps 8-9 with test tube P. PROCEDURE 5: Catalyst Affects 1. In the left well of the next empty row place 8 drops of KI solution. 2. Add 2 drops of HCl solution to the KI in the well. 3. Add the number of drops of sodium thiosulfate determined in Procedure Add 4 drops of starch solution to the mixture. 5. Add 2 drops of DI water to the solution in the well. 6. Swirl the mixture by moving the well plate in small circles on the table. 7. Using the pipeter, add 0.4 ml of 3% H 2 O 2 to the same well. Begin timing immediately after the addition of the H 2 O 2 to the well. 8. Swirl the solution and monitor the color. Record the time it takes for the entire solution to turn 9. Repeat steps 1-8 using 2 drops of CuSO 4 solution in place of the DI water. Results Procedure 1: Calibration Table Trial # Na 2 S 2 O 3 Drops Time Procedure 2: Concentration Changes Trial # ml KI ml DI Time AccelLab23-RxnRates 3

4 Procedure 3: Temperature Changes Trial Water Temperature Time Room temp Hot Water Bath Cold Water Bath Procedure 4: Surface Area Changes Surface Area Time Powder Crystals Procedure 5: Catalyst No Catalyst Time Catalyst Analysis: 1. Why was the initial calibration procedure necessary for this experiment? 2. Why was DI water necessary in Procedure 2? Why couldn t you simply reduce the number of drops of KI? 3. How does a change in concentration affect the rate of reaction? Explain using collision theory. 4. Explain using collision theory the effect of increasing the reaction mixture temperature on the rate of reaction. Use your data as evidence. AccelLab23-RxnRates 4

5 5. Explain using collision theory the effect of increasing the surface area of a reactant on the rate of reaction. Use your data as evidence. 6. Which procedure would be the best option for I 3 - /starch complex synthesis for the pharmaceutical preparation procedure? Explain why you chose this procedure. AccelLab23-RxnRates 5