A Kinetic Study of the Base Catalyzed Cleavage

The University of Lethbridge De arrayment of chemistry & Biochemistry alchemy 2740 science lab sample 2 A KINETIC STUDY OF THE BASE CATALYZED cleavage OF DIACETONE ALCOHOL USING A DILATOMETER The depravation of diacet one(a) alcohol into deuce molecules of acetone is catalyzed by hyd markd oxide ions and is an example of an aldol muscular contraction in reverse. O OH OHO 2CH3-C-CH3 CH3-C-CH2-C(CH3)2 The valuate of dis beattlement is archetypical-order with respect to the concentrations of both diacetone alcohol and hydroxide ion Rate = kOH-diacetone alcohol (1)However, since hydroxide ion is a accelerator its concentration remains constant during the reaction. The boilers suit reaction come forths root-order (i. e. is a pseudo showtime order reaction) and bes the observable rate law Rate = k diacetone alcohol where k = k OH- (2) Since the boilers suit reaction is first-order we fundament study the kinetics of the reaction by metre whatsoever property of the s ystem that undergoes a diversity which is proportional to the extent of reaction. Such a property in this guinea pig is the peck of the reaction ascendant.The effective pot of one molecule of diacetone alcohol is not the like as the effective volume of twain molecules of acetone and as a closure the total volume of the reaction solution changes as the reaction buy the farms. In this event the solution expands although in some reactions it contracts. A simple instrument for measuring volume changes is a dilatometer which consists of a glass electric-light light myelin to which is attached a thermionic vacuum tubing with a s clear upcock (for woof the bulb) and also a piece of long capillary vessel tubing.The bulb is fill with reaction solution to the put where semiliquid comely enters the capillary pipage and hence the putz on the option provide is closed. As the solution expands it does so into the capillary supply ca apply the semilunar cartilage in the t ube to raise. By measuring the distance up the capillary tube that the semilunar cartilage travels one has a st oxygenate of the volume change. star tush forge the actual volume change if the crosssectional body politic of the capillary is known but so far that is not necessary in this taste.Since the couch of the semilunar cartilage in the capillary chromatography column provide be measured accurately using a cathetometer, this is a bully experiment to test the Guggenheim order for find out first-order rate constants (refer to Appgoalix A on First-order Reactions). In this method immortaliseings be largely do at generation t0, t1, t2, t3, etcetera , with apiece reading page 2 1 chemical science 2740 Laboratory Experiment 2 taken at a constant, accurately determined time time interval after the preceding measurement. The resulting selective information lean is divided into equal halves.For example, if there are 20 readings taken at times t 0 t19 with co rresponding measurements P0 P19, the entropy would be divided in deuce between readings P9 at t 9 and P10 at t10. Next, the differences between the measurements in the two data sets are taken, i. e. , P0-P10, P1-P11, P2-P12, etc. notification that the time interval between to each one pair of readings is constant. Finally a diagram of the natural logarithm of the differences against time, i. e. , ln(P0-P10), ln(P1-P11), vs. t0, t 1, should stick out a straight line of position -k, the first-order rate constant.Apparatus Cathetometer, 3 dilatometers, timer. A dilatometer is a device for measuring the elaboration (or contraction) of a liquid. Ours is of carnal knowledgely simple design and was made locally by Luis Delgado from various pieces of glassware. It consists of an intricacy bulb to which is attached a handsome capillary tube with a designate and hopefully uniform bore. The expansion tube is connected at the other end to a fill up tube through a stopcock. When the stopcock is closed, a solution in the expansion tube can only expand up the capillary tube.The volume of liquid in a capillary or cylinder is devoted by the cross-sectional area, A, of the cylinder times its length, l (V = A x l). and then by measuring the travel, ? l, of the liquid up the capillary tube one has a quantity that is proportional to the change in volume of the reaction kind (? V = A x ? l). As a result one can follow first order reactions with a dilatometer and social function the first order equation ln (lo l? ) / (lt l? )= kt Stopcock Capillary tube Filling tube Expansion bulb (3) A Dilatometer and other equations such as the Guggenheim equation that are derived from it to analyze the results.This assumes that ? l (and therefore ? V) is proportional to the extent of reaction. One essential be careful with thermostating when using a dilatometer. A dilatometer, after all, is a glorified thermometer and a quite highly sensitive one at that. Thus the frame-up an d the reaction solution must be pre-equilibrated to the temperature of the reaction. The Page 2 2 Chemistry 2740 Laboratory Experiment 2 dilatometer is filled by pouring reaction ad variety into the filling tube. Try to pour dump the centre of the tube and not raven the walls of the tube.Also do not fill the filling tube in a higher place the level of the piddle in the pee clean because the part of the filling tube above water level pull up stakes not be comfortably thermostated. Next the reaction mixture must be forced into the expansion bulb by use of a rubber bulb applied to the top opening of the filling tube. Often air bubbles become trapped just beneath the stopcock. These can be sequestrated by sucking back with the rubber bulb. shroud to add more reaction mixture to the filling tube, as necessary. Force reaction mixture into the expansion bulb until the liquid level reaches the top of the bulb just below the capillary tube.Stop forcing liquid into the bulb and depart the liquid level to rise into the capillary tube as a result of the flow of liquid from the filling tube to the expansion bulb. DO not FORCE LIQUID INTO THE CAPILLARY TUBE. oddment the stopcock. The dilatometer is now ready for making measurements of the meniscus point. The cathetometer is a device for measuring the relative height of the liquid column in the capillary. It consists of a vertical steel celestial pole with a scale marked on its length and a oscilloscope that exits up and down the rod.In operation one measures the height of the liquid column by pathetic the telescope so that the cross-hair is focussed on the meniscus of the liquid column. The position of the telescope (and thus the meniscus) is then read absent the scale on the bar with the financial aid of a vernier. Ensure that you can read the vernier scale (refer to Appendix B on Reading a vernier scale) and can operate the telescope (focus, doing up and down, and leveling) before proceeding with measurements. Reagents Diacetone alcohol, 0. 40 M NaOH. Waste Disposal A 4-litre bottle for the collection of bungles is supplied with the experimental set up.All excess stock reagents and reaction solutions should be disposed of in this bottle. The glassware can then be given a single small rinse into the waste container before macrocosm cleaned further in the sink. In preparing reaction solutions only remove as much reagent from the stock container as is necessary to make the reaction mixtures. Page 2 3 Chemistry 2740 Laboratory Experiment 2 Procedure Notes 1) In order to finish this lab in the time allotted, students must be well organized and prepared to drink down this experiment at the beginning of the period. 2) The 0. 40 M NaOH solution impart need to be raiseardized by each group.This can be done before or after the experiment is completed, but must be done before the calculations for the work are started. Students can arrange a suitable time for this with their in structor. (Note A confusable task was performed in Chemistry special K lab it may be subservient for you to review that physical process. ) Three kinetic runs should be performed at hydroxide ion concentrations of approximately 0. coke, 0. two hundred and 0. cd M. Prepare 100 mL each of 0. 100 M and 0. two hundred M sodium hydroxide solutions from the 0. cd M solution provided. Allow a dilatometer to thermostat in the 25 C water bath. Pipette merely 50 mL of 0. 00 M NaOH solution into a 200 mL Erlenmeyer flaskful, stopper the flask, and forfeit it to thermostat in the bath as well. When the dilatometer and sodium hydroxide solution check been thermostated for at least 10 minutes, start the reaction by adding with a pipet 2 mL of diacetone alcohol into the flask containing the 50 mL of 0. 100 M NaOH solution. Stopper the flask, shake it vigorously to hold in mixing and then let it stand in the water bath for a short period to allow the bubbles to settle. shoot the settl ed solution into the filling tube of the dilatometer and proceed to fill the dilatometer as sketch above.When the solution enters the capillary close the stopcock on the filling tube ensuring that no bubbles remain in the bulb. Clamp the dilatometer hard in place in the bath so that the expansion bulb is cover with water. Commence reading the height of the meniscus in the capillary column with the cathetometer and restrain to do so at precisely 3-minute intervals for at least 15 readings (45 minutes). The first reading can be obtained by clamping the telescope so that the cross-hair is just above the meniscus start the clock as the meniscus climbs to the crosshair. Because the telescope inverts its image, the meniscus will appear to be below the cross-hair when it is truly above and the meniscus will appear to be travelling down when it is very travelling up the capillary. ) Subsequent readings will require close cooperation between lab mates. One person should follow the men iscus with the telescope while the other partner gives out the time so that the first partner can clamp the telescope in position at exactly 3-minute intervals. Page 2 4 Chemistry 2740 Laboratory Experiment 2 When the readings soak up been completed put the dilatometer aside and proceed to the second experiment.While the first experiment is being performed, the dilatometer and the 50 mL of sodium hydroxide solution for the second experiment should be clamped in the bath to thermostat. Repeat the procedure using 0. 200 M NaOH and 0. 400 M NaOH in place of 0. 100 M NaOH and with time intervals of 1. 5 and 0. 75 minutes respectively. In the case of the run using 0. 400 M NaOH, allow the reaction to go to completion and then read the height of the meniscus. Before sledding the laboratory, please enter names, date, and experimental data into the computer. DO NOT FORGET TO cipher YOUR STANDARDIZATION DATA INTO THE COMPUTER erstwhile YOU HAVE OBTAINED IT.Calculations and Report Use th e Guggenheim method to maneuver the apparent first-order rate constants (k) for each run. For the last run, also calculate k using equation (3). Compare the rate constants mensurable by the two methods and demonstrate the validity of using the Guggenheim method to calculate rate constants (i. e. discuss if the evaluate calculated using the Guggenheim method compares favourably to the value calculated using the standard method). bode the second-order rate constants (k) in each case and discuss this confirmation of the first-order dependence on hydroxide ion concentration. Page 2 5