CHEM 110 - Lab 1 Method.docx

**[Time Management Method -- Lab 1 CHEM 110 -- Jasmine Kaur]** 4.4. Experiment -- Synthesis of Aspirin.\ Preparation of aspirin: - Make an ice bath by filling a plastic pot (found next to the ice machines) with ice and adding \~25mL of cold tap water.  Aspirin Synt...

**[Time Management Method -- Lab 1 CHEM 110 -- Jasmine Kaur]** 4.4. Experiment -- Synthesis of Aspirin.\ Preparation of aspirin: - Make an ice bath by filling a plastic pot (found next to the ice machines) with ice and adding \~25mL of cold tap water.  Aspirin Synthesis (continued):  - Collect and set up vacuum filtration equipment. - Make another ice bath by filling a plastic pot (found next to the ice machines) with ice and adding \~25mL of cold tap water. - Vacuum filter the aspirin from aspirin synthesis.  - Run the TLC plate. Aspirin from Recrystallisation: - Pre-weigh petri-dish. - Calculate the theoretical yield. - Do write up! Collect the aspirin from the purification of aspiration: Analyse the TLC plate:  **[Lab Notes (Pre-Lab 1):]** - It is important to note that we only touch the edges of the plate, and we do this step carefully. This is because compounds on our hands can get absorbed onto the plate, which may disrupt the results. - The \'solvent front\' means the point upto which the solvent had reached on the plate. Which should be marked with a pencil, since it is thin, and does not require much pressure. This should be done as precisely we can, so the correct calculations can be taken. - For accuracy, look at the measuring cylinder at eye level, making sure the measurement of 5mL is taken from the bottom of the meniscus. - Since the reaction vial may be hot, would it be best to remove it using tongs, due to the high temperature? - For time-management, the ice bath should be prepared earlier, during the aspirin synthesis. As it also means the experiment can continue, without any hurdles. - For the theoretical yield, do we use the moles of the limiting reagent, then using the mole ratio to find the moles of the theoretical product (Aspirin)? Then convert that to mass using the equation: m=nM. The mass found is therefore the theoretical yield? - Make sure that too much pressure is not applied when making the dot(s), because it may cause unnecessary holes on the TLC Plate. - = (distance travelled by the spot) / (distance travelled by the solvent) - Is the mole ratio required different from the mole ratio used/formed? Due to Salicylic Acid and Acetic Anhydride having different moles used/formed? - It is important to record observations during the experiment at each stage. Such as changes in appearance, colour or smell. Do we record these on the report sheet? - Is it best to use a timer or stopwatch since devices are not allowed? Or check the time on the clock in the laboratory? - Make sure that all of the product is transferred to the petri dish, to maximise the yield. - Make sure to use a different capillary dropper to avoid cross contamination, and make sure that the spots do not bleed into one another. Following up on \@Maria Lee\'s comment which was very helpful. It is also important that the \"used\" capillary dropper is placed into the \"used beaker\" to avoid any confusion. And a clean one is used from the \"clean beaker.\" - \@Maria Lee Yes, that seems like a good idea. There may be a tool we can use on the edges, which will allow us to reduce this risk. - \@Maria Lee Yes. We need to make sure to use a \'Buchner Flask\' and clamp it to the retort stand. And attach the vacuum tube which should be turned off as you mentioned. Then place the \'Buchner Funnel\' on top. Then we turn the vacuum onto full. We need to use filter paper which should be wet from the solvent (ice-water) and place it into the funnel. It is important for all the contents to be swirled and poured into the funnel, to maximise the yield. Hope this helps! - \@Sammy Fookes This is a good question! Since they have mentioned the hotplate to be set to a specific temperature (150°C), I think it \'hot\' would be reaching that temperature. - I agree, my only concern though is that due to energy lost to the external environment and equipment as it transfers from the hotplate to the solution, it seems unlikely that the solution will ever reach the same temperature as the hotplate? - \@Sammy Fookes Yes, that is true as well, energy may be lost to the external environment due to this. I think it may mean to reach as close to the temperature possible. Sufficiently hot, I would say. - \@Maria Lee Thanks for confirming!! - This distance is measured in cm, from the baseline (from the original spot). - Yield (mass) of the product (Aspirin) by conducting the experiment. - \"Working up the reaction.\" - This should also include long-hair to be tied back, as it may cause problems when conducting the experiments. Such as chemicals on the bench touching hair. - My understanding is that an excess of ethanoic anhydride is used to improve the yield of the synthesis of aspirin by moving the reaction\'s equilibrium to favour the products? - My understanding is that boiling chips are added to make sure the solution is heated \"smoothly\" and \"evenly.\" It may provide the right surface? - Note: phosphoric acid is used here as a catalyst and to speed up the rate of reaction - This is effective as scratching the inside of the glass gives the crystals a rough surface to start growing on - solution should start to get cloudy - It will be necessary to prepare a second ice bath for the *Purification of Aspirin*, (and not reuse the original one from the *Synthesis of Aspirin* which will have warmed up significantly since it was prepared). This would likely be most suitable to do during the time the purified aspirin is left to stand at room temperature. - Emphasis on \"carefully draw\" because the silica gel on the plate is a very thin layer and drawing with too much force may scratch it. - Use mole ratio and the moles used to find moles formed of aspirin - use this to find the mass of aspirin made (via n=m/M) - \% Yield = (Experimental Yield)/(Theoretical Yield) x 100.