Aognity 202 11 Collected practicals lb. Purification technique: recrystallisation After a substance is separated, it may still contain some impurities from the mixture and require an additional step or ‘clean’ or purify the sample. Added impurities add to the mass and can alter the physical properties of the substance. For example, when a precipitate is filtered, it will initially have water present as an impurity and after drying, the water evaporates leaving behind the dry solid. What if there are other solid substances present in the dry precipitate that need removal? How can the solid substance be ‘cleaned’? One method for purifying crystals is known as recrystallisation. In this process, the crystals are dissolved in a liquid solvent, usually ethanol, and then cooled and filtered again, The impurities will dissolve in the solvent, leaving the cleaned crystal behind, as shown in Figure 1. This method is not suitable for all substances and risks losing some of the sample in the process. is Cover with watch - glass to prevent = evaporation and contamination = he =. E °° tae Dissolve impure Allowsolutionto _Placeflaskin _Filter crystals by mixtureinasmall cooltoroom —icebathtocool__ vacuum filtration volume ofhot temperature so further solvent that crystals begin to form Figure 1. Method for recrystallisation. Tae aur Fen 30 Boy Tal K bitps app kognity.comstudy/appetass-b-dp-cnemistry-sIh62025-newisls426.cld-372088/book/purlaton-technique-recystalsalon-Tb-d-A67 "31... 14ani24, 2:13 PM titps app kognily.convstudy/appelass-b-dp-chemistry-sIh 62025-new/si-426-cid-372088/book/purfcaion-technique-recystalsalon-10-4-4673 1b, Purification technique: recrystaliston | IB OP Chemisty SLIML FE2025 (NEW) Purification of aspirin tablets using recrystallisation Aspirin is a common medication used as a pain reliever, fever reducer and blood thinner, The active ingredient in aspirin is acetylsalicylic acid, but the tablets contain other substances that allow the pills to be easily swallowed and have a longer shelf-life. These other substances can be thought of as impurities. In this experiment, you will purify aspirin tablets using recrystallisation. Practical skills In this practical you will be exercising the following tools and skills: Tool 1: Experimental techniques + Measuring variables: understand to accurately measure to an appropriate level of precision: mass and volume. * Applying techniques: recrystallisation and drying to a constant mass. Materials required * Mortar and pes © 100 cm? beaker * 100 cm? graduated cylinder © Stirring rod + Hot plate * Ice water bath © Apparatus for filtration © Filter paper © Aspirin tablets ¢ Ethanol * Iced distilled water Ke 218‘26, 2:19 M 1b, Purification technique: recrystaliston | IB OP Chemisty SLIML FE2025 (NEW) Procedure 1. Record the mass of two aspirin tablets. 2. Crush the tablets with a mortar and pestle and transfer the contents to the beaker. 3. Measure 20 cm} of ethanol with the graduated cylinder and add to the beaker. 4. Heat gently on a hot plate, stirring until the crystals dissolve. 5. Immediately remove the beaker from the hot plate and add 40 cm} of ice water to the beaker and place the entire beaker into the ice water bath. 6. Stir rapidly until white crystals form. 7. Set up apparatus for filtration (gravity or vacuum). Collect the crystals (residue) on pre-massed filter paper and discard the filtrate. 8. Dry the crystals overnight and record the mass of the crystals on filter paper. Determine the mass of the purified crystals and compare to the original mass of the two tablets and to the mass of acetyl salicylic acid noted on the packaging, Data analysis Record your qualitative and quantitative data in a prepared table. All data should be handwritten in ink with mistakes crossed out with a single line, such that the words can still be read, Organise your table in the sequence of the procedure, writing down the information as you go. Qualitative observations should be simple and in point form and quantitative observations should include all necessary units and uncertainties. Preparation for recrystallisation: Table 1, Preparation for recrystallisation. Ke itps app kogniy.constudy/appetass-b-dp-cnemistry-slh62025-newisls426-cd-372068/book/purlaton-technique-recystalsalon-1b-d-A67 "31... 9/4‘26, 2:19 M 1b, Purification technique: recrystaliston | I8 OP Chemistry SLIML FE2025 (NEW) Qualitative Mass (g) observations Two aspirin tablets Dry filter paper Crystals and dry filter paper Processing of data: 1. Determine the mass of the dry crystals. 2. Compare the mass of the dry crystals with the mass of the original aspirin tablets before recrystallisation. What percentage of mass was lost? 3. Compare the mass of the dry crystals with the mass of the active ingredient (acetyl salicylic acid) in the aspirin tablets as stated on the label. Does the evidence suggest that your recrystallised product still contains impurities? Does the evidence suggest that you lost some of the active ingredient in the proce: Internal assessment checklist For your internal assessment work, remember the following that you have exercised in this practical: ‘+ Understand the process of solvation to produce homogeneous and heterogeneous mixtures. ‘+ Know which technique and equipment to use for separating a variety of mixtures - filtration, evaporation, distillation and paper chromatography. ‘+ Know how to purify a sample using recrystallisation. Ke hitps app kognity.comstudy/appetass-b-dp-cnemistry-sIh62025-newisls426-cld-372068/book/purlaton-technique-recystalsalon-Tb-d-A67 "31... 44