Kinetics and Preliminary Experiments - Lab Report Example

Kinetics Lab Procedure Preliminary Experiments Take a 50 mL beaker from the Glassware shelf and place it on the workbench. 2. Move it to the"top" of the workbench so the white wall is seen behind it which will make it easier to see the color change 3. Add 5.0 mL of 0.2 M KI solution from the Chemicals shelf to the beaker. 4. Dilute the 0.2M KI solution by adding 10.0 mL of water from the Chemicals shelf to the beaker. 5. Add 0.15 mL of the starch indicator from the Chemicals shelf to the beaker. When starch,(I), is present the starch indicator combines with it and makes the solution a blue-black color. 6. Add 5.0 mL of 0.2 M (NH4)2S2O solution from the Chemicals shelf to the beaker. The ammonium persulfate reacts with the free iodine ions from the potassium iodide in solution to produces iodine molecules. Observe the beaker and record any color changes. 1. What are the colors of the following ions: K+ and I- Colorless in water 2. What is the color of the starch*I2 complex Blue Black Kinetics Experiments Trial 1 1. Take a 250 ml beaker from the Glassware Shelf and place it on the workbench. 2. Add 25 ml of 2 M NaI solution from the Chemicals Shelf to the beaker. 3. Add 1 ml of starch indicator and 0.05 ml of 0.1 M EDTA solution from the Chemical Shelf to the same 250 ml beaker. This drop of EDTA solution is to minimize the effects of trace quantities of metal ion impurities that would cause spurious effects on the reaction. 4. Take a timer from the upper right hand corner of the screen and place it on the workbench. Wait till you obtain a round number on the timer to begin timing the reaction. Be ready to begin timing the reaction when you add the ammonium persulfate to the solution in the 250 mL beaker. 5. To begin the reaction, add 25.0 mL of the 0.2 M ammonium persulfate solution from the Chemicals shelf to the 250 mL beaker. 6. Record the time for the appearance of the black color.20 Trial 2 1. Take a 250 ml beaker from the Glassware Shelf and place it on the workbench. 2. Add 25 ml of 2 M NaI solution from the Chemicals Shelf to the beaker. 3. Add 1 ml of starch indicator and 0.05 ml of 0.1 M EDTA solution from the Chemical Shelf to the same 250 ml beaker. This drop of EDTA solution is to minimize the effects of trace quantities of metal ion impurities that would cause spurious effects on the reaction. 4. Take a timer from the upper right hand corner of the screen and place it on the workbench. Wait till you obtain a round number on the timer to begin timing the reaction. Be ready to begin timing the reaction when you add the ammonium persulfate to the solution in the 250 mL beaker. 5. Prepare a 0.1 M solution of ammonium persulfate by diluting the 0.2 M solution. To do this take a 50 ml beaker from the Glassware Shelf and place it on the workbench. Add 12.5 ml of water and 12.5 ml of 0.2 M ammonium persulfulate. 6. To begin the reaction, add the contents of the 50 ml beaker to the 250 ml beaker by dragging the 50 ml beaker on top of the 250 ml beaker and selecting all. 7. Record the time for the appearance of the black color. 16 ml of Ammonium persulphate Trial 3 1. Take a 250 ml beaker from the Glassware Shelf and place it on the workbench. 2. Add 25 ml of 2 M NaI solution from the Chemicals Shelf to the beaker. Dilute the NaI solution to 0.1 M by adding 25 ml of water. 3. Add 1 ml of starch indicator and 0.05 ml of 0.1 M EDTA solution from the Chemical Shelf to the same 250 ml beaker. This drop of EDTA solution is to minimize the effects of trace quantities of metal ion impurities that would cause spurious effects on the reaction. 4. Take a timer from the upper right hand corner of the screen and place it on the workbench. Wait till you obtain a round number on the timer to begin timing the reaction. Be ready to begin timing the reaction when you add the ammonium persulfate to the solution in the 250 mL beaker. 5. To begin the reaction, add 25.0 mL of the 0.2 M ammonium persulfate solution from the Chemicals shelf to the 250 mL beaker. 6. Record the time for the appearance of the black color. Complete the Table Trial # [I-] Moles [S2O82-] Moles Time (sec) Rate = [S2O82-] / time Moles/sec 1 0.001 0.003645 20 0.000183 2 0.001 0.001487 41 0.000036 3 0.0005 0.003956 56 0.000070 Molecular: 2Na2S2O3 + I2 ( excess from primary reaction) 2NaI + 2Na2S4O6 Net Ionic: 2S2O3 2- + I2 2I- + 2S4O62- The rate law for this reaction is: rate 1 = k[S2O82-]x[I-]y = 0.000183*[0.003645]x*[0.001]y For experiment 2, the concentration of S2O82- has been reduced by 50% so the rate law will become: Rate 2 = k(0.5[S2O82-])x[I-]y = 0.5x * rate 1 For experiment 3 the concentration of I- has been reduced by 50% so the rate law becomes: Rate 3 = k[S2O82-]x(0.5[I-])y = 0.5y * rate 1 What is the value for x __1_________ What is the value for y __2_________ What is the value for k and its units moles/sec 2. Give an example of a laboratory exercise that you feel would be more effective in demonstrating chemical kinetics 3. Discuss the particulars of one such reaction here, and clearly explain the benefits or methods associated with your example An example of another reaction that can also be used to demonstrate Chemical Kinetics is to determine the rate at which the Phenolphthalein indicator which gives a colorless to pink indication at the end of acid base titrations is allowed to stand for a few more minutes. Though the solution is colored pink in the course of time it returns back to the colorless solution as the phenolphthalein reacts with the OH- ion in a strongly basic solution. A graph of the concentration of phenolphthalein in mol/L Vs Time (sec) can then be plotted which gives us an illustration as to by what factor is the phenolphthalein concentration is falling as a function of time. It is convenient to perform this reaction as it is commonly occurring, does not require elaborate reagent preparation and can be monitored simultaneously alongwith any routinely carried out titration. Moreover it is a simple first order reaction where Reaction rate = k(phenolphthalein) Thus the reaction rate is simple to measure and calculate also. To study some more aspects concerned with chemical kinetics a few other experiments could be designed. The same prescribed reaction could be carried out at various temperatures to study the effect on the rate of the reaction. Also a catalyst such as Copper sulphate could be used in the same reaction as performed on latenitelabs to study the effect of catalysis on the rate of reaction. Read More