CHMA2000 EXPT 2: Recrystallization Experimental Objectives: At the end of this experiment you should be able to: 1. Perform a recrystallization 2. Determine the best solvent for the recrystallization of a specific compound 3. Calculate percentage yield 4. Assess the purity of a compound using melting point determination Prelab Exercises: Before coming to lab you should: 1. Read about recrystallizations and the experiment and its background. 2. Prepare a flow chart as appropriate for the lab exercise. 3. Note the theoretical solubilities of compounds listed in procedure 1 (make a table). 4. Prepare a results table for your report (as suggested below) 5. Determine the solubility of acetanilide at approximately room temp from reference sources Procedure: Choice of Solvent: (work in pairs!!) Test the solubility of (a) aspirin, (b) naphthalene, (c) acetamide, (d) sucrose, (e) benzoic acid, and (f) vanillin in each of four solvents by using the directions which follow. Record all results in a properly constructed table. Weigh 0.5g of solid to be tested, and divide the sample into four equal parts. Stir one portion with 2mL of water in a test tube and record the solubility. If the material fails to dissolve, boil the mixture over an open flame and record the solubility in the hot water. Stir a second portion of the solid with 2mL of cold ethanol and note the solubility. If it fails to dissolve, heat the mixture in a water bath (DANGER the solvent will ignite if heated in a flame) and note the results. Similarly test the solubility of the third portion in 2mL of cold toluene, then in toluene which is heated in a water bath. Use the last portion of the solid to test its solubility in 2mL of cold ethyl acetate, then in ethyl acetate heated in a water bath. In recording observations (in a table) use the letters S, soluble or I, insoluble.
Recrystallization of Impure Acetanilide: (Work in Pairs!!) Weigh a 3.0g sample of impure acetanilide of unspecified purity (prepared from acetanilide, sucrose, sand and powdered charcoal) and place in a 150mL beaker. Add 50mL of distilled water and heat the mixture to almost boiling. (Be careful not to boil off the water!!) In order to dissolve all the acetanilide in the mixture it may be necessary to add a small amount more hot water. At the same time as the heating of the impure acetanilide is taking place assemble a filtering apparatus as shown in prelab/lab. Moisten down the cotton wool with hot water (ensure that no more than 25mL of water is in the Erlenmeyer flask... Do not let this go dry!!!). Pour the hot acetanilide mixture through the heated funnel apparatus. Rinse the beaker with hot solvent (water in this case). Pour the rinse through the heated funnel. Use as little rinse as possible. Remember that it is important that the solution and the apparatus are hot to prevent premature formation of crystals. Once the solution has been filtered place the Erlenmeyer flask containing the purified acetanilide and water in the ice bath for approximately 10-15 minutes or until crystallization is complete. (You may have to induce crystallization - ask the instructor if necessary) Assemble a Buchner funnel apparatus (as shown in prelab/lab). Using double filter paper moistened with cold solvent. Filter the crystallized material using vacuum filtration. Small amounts of cold solvent may be used to rinse down the flask and to wash the crystals. Leave the crystals to dry using the vacuum. Meanwhile take a very small quantity of the drying material and an unglazed porcelain tile. Using the procedure outlined by the instructor, dry the purified product and determine the melting point range. Once the crystals have vacuum dried (about 10-15 minutes) mass the purified acetanilide, examine the crystals and determine the percent yield. Suggestions for your Lab Report: (FORMAL REPORT THIS WEEK) Remember to put your name, partners name(s) and date expt done. Do not use liquid paper products in your report. For part 1: be sure to indicate (in a table) which of the four solvents (if any) would be suitable for recrystallization of naphthalene, aspirin, acetamide, sucrose, benzoic acid, and vanillin.
For part 2: compare the melting point of purified product with literature melting point (from ref source). Your conclusion should NOT be the purpose was fulfilled. Please ask if you are not sure. A complete list of references are required for all lab reports. Please use an appropriate format and PLEASE ASK if you are not sure. Remember to answer the questions! Questions: (Literature search required for questions) 1. Could acetamide be separated from acetanilide by recrystallization from 2. Could naphthalene be separated from acetanilide by recrystallization from 3. Could benzoic acid be separated from acetanilide by recrystallization from 4. What volume of water should be used to recrystallize a 5g sample of benzoic acid? How did you derive your answer? Safety for Experiment 2: Recrystallization REMEMBER, IF YOU ARE NOT SURE ABOUT ANYTHING ASK BEFORE YOU START WORK IN THE LAB ALL ACCIDENTS MUST BE REPORTED TO LAB INSTRUCTOR. EYE PROTECTION MUST BE WORN AT ALL TIMES IN CHMA2000 LABS The information on this page is a brief overview of safety issues for this experiment. Please read this BEFORE starting work in the lab. If you have any concerns or questions please ask your lab instructor BEFORE you start work in the lab. TOLUENE - Is considered to be highly flammable. Inhalation of the vapours may cause dizziness, headache, nausea, and mental confusion. The vapours and
the liquid will irritate the eyes and the mucous membranes. Absorption through the skin and ingestion will cause poisoning. Breathing of vapours over long periods may cause blood diseases. Prolonged contact may cause dermatitis. Standard first aid treatment. MSDS # 525 ETHYL ACETATE Is considered to be highly flammable. The vapours may irritate the eyes and respiratory system. The liquid irritates the eyes and the mucous surfaces. Prolonged inhalation may cause kidney and liver damage. Standard first aid treatment. MSDS # 218 ETHANOL Is considered to be highly flammable. Avoid breathing vapour in high concentrations. Standard first aid treatment. MSDS # 1278 NAPHTHALENE - Causes eye and skin irritation. Harmful if swallowed, inhaled, or absorbed through the skin. Vapours or mist is irritating to the eyes, mucous membranes and the upper respiratory tract. Exposure can cause nausea, headache and vomiting. May cause allergic skin reaction. Standard first aid treatment. MSDS # 355 BENZOIC ACID - Irritant. May be harmful by inhalation, ingestion, or skin absorption. Causes eye and skin irritation. Material is irritating to the mucous membranes and the upper respiratory tract. Standard first aid treatment. MSDS # 832 ACETAMIDE - Carcinogen. Harmful if swallowed, inhaled or absorbed through the skin. Standard first aid treatment. MSDS # 3 ACETANILIDE - Irritant. May be harmful by inhalation, ingestion or skin absorption. Causes eye and skin irritation. Material is irritating to the mucous membranes and the upper respiratory tract. May cause cyanosis. Standard first aid treatment. MSDS # 2 VANILLIN - May be harmful if inhaled. May be harmful if absorbed through the skin. Causes eye irritation. May cause skin irritation. Standard first aid treatment. MSDS # 2011
DISPOSAL: All organic material must be disposed of in the organic waste containers found in the fume hood. Purified acetanilide should be placed in the appropriate beaker found on the front bench. Cover slips/capillary tubes MUST be disposed of in garbage cans marked for broken glassware. The MSDS numbers above refer to Material Safety Data Sheets which are available for review in Dept. of Environmental Sciences, please ask Ms. Tate or Mr. Fergus for access to these sheets. Last updated May, 2016 J. Hoyle & M. Tate, 2016