ORGANIC CHEMISTRY I CHEMISTRY 261. MACEWAN UNIVERSITY Winter 2016

Transcription

1 ORGANIC CHEMISTRY I CHEMISTRY 261 MACEWAN UNIVERSITY Winter 2016

2 LABORATORY INFORMATION SAFETY a. PERSONAL PROTECTION b. LABORATORY ACTIVITIES USING CHEMICALS a. HANDLING/DISPENSING b. SPILLING c. DISPOSING d. ACCIDENTS INVOLVING CHEMICALS

3 LABORATORY INFORMATION EQUIPMENT a. LOCATION b. GLASSWARE: BREAKAGES AND DISPOSAL LAB EXPERIMENTS a. PREPARATION: HAZARDOUS PROPERTIES b. DATA SHEET c. LAB REPORT d. QUIZZES e. EXTRA HELP

4 ADVANCED PREPARATION PRE-LAB POWERPOINT SLIDES ARE POSTED TO BLACKBOARD FOR VIEWING BEFORE AND AFTER THE LAB. A SAMPLE LAB EXAM WILL ALSO BE AVAILABLE ON BLACKBOARD

5 EXPERIMENT 1: RECRYSTALLISATION OF BENZOIC ACID A PURIFICATION METHOD WHICH INVOLVES DISSOLVING AN IMPURE SOLID IN A HOT SOLVENT AND THEN SLOWLY COOLING THE SOLUTION TO PROMOTE CRYSTALLISATION OF THE PURIFIED SOLID.

6 SOLVENT CHOICE THE SOLID SHOULD BE PRACTICALLY INSOLUBLE (OR SPARINGLY SOLUBLE) IN THE SOLVENT AT LOW TEMPERATURES AND READILY SOLUBLE IN THE SOLVENT AT HIGH TEMPERATURES (CLOSE TO THE B.P. OF THE SOLVENT). SOLUBILITY OF BENZOIC ACID IN WATER (100 ml) 17 C C IMPURITIES EITHER: REMOVAL OF IMPURITIES REMAIN INSOLUBLE AT ALL TEMPERATURES (REMOVED BY FILTRATION, BEFORE RECRYSTALLISATION). REMAIN SOLUBLE AT ALL TEMPERATURES (REMOVED BY FILTRATION, AFTER RECRYSTALLISATION).

7 1. SETTING UP THE EXPERIMENT HEAT D.I. WATER (TO BE USED AS THE RECRYSTALLISATION SOLVENT) IN A 125mL ERLENMEYER FLASK. YOU DON T NEED TO WAIT FOR THIS TO BOIL BEFORE PROCEEDING. ACCURATELY WEIGH g OF CRUDE BENZOIC ACID INTO A 50mL ERLENMEYER FLASK. REMEMBER TO ADD BOILING STONES!

8 2. OBTAINING A SATURATED SOLUTION DISSOLVE THE BENZOIC ACID IN THE MINIMUM AMOUNT OF BOILING WATER.

9 3. COMMENCING RECRYSTALLISATION CAREFULLY REMOVE THE RECRYSTALLIZATION FLASK FROM THE HOTPLATE. ALLOW THE FLASK TO COOL SLOWLY AND UNDISTURBED TO ROOM TEMPERATURE. COOL THE FLASK FURTHER BY PLACING IT IN AN ICE BATH FOR AN ADDITIONAL MINUTES.

10 4. ISOLATING THE CRYSTALS: VACUUM FILTRATION SET UP THE APPARATUS FOR VACUUM FILTRATION. SWIRL THE CONTENTS OF THE ERLENMEYER AND QUICKLY FILTER THE SLURRY. WASH THE CRYSTALS WITH 2 2mL PORTIONS OF ICE COLD WATER.

11 5. ISOLATING THE CRYSTALS: DRYING ALLOW THE CRYSTALS TO DRY UNDER DYNAMIC VACUUM FOR ~ 10 MINUTES. TRANSFER THE CRYSTALS TO A LABELLED, PRE-WEIGHED VIAL AND RECORD THE MASS. RECORD THE MELTING POINT OF BOTH THE CRUDE AND PURIFIED BENZOIC ACID.

12 6. DETERMINING THE MELTING POINT 1. PREPARE SAMPLE BY CRUSHING TO A FINE POWDER. 2. LOAD SAMPLE INTO CAPILLARY TUBE (2-3mm DEPTH).

13 STEPS IN DETERMINING A MELTING POINT 3. HEAT SAMPLE FAIRLY RAPIDLY (~10 C/MINUTE) UNTIL C BELOW THE EXPECTED M.P. 4. SLOW RATE OF HEATING TO ~1-2 C/MINUTE. 5. TAKE MELTING POINT RANGE (& SINTERING TEMPERATURE, IF OBSERVED). 6. ANALYSE M.P. RANGE AND VALUE.

14 RECORDING AN ACCURATE MELTING POINT WHEN C BELOW THE EXPECTED M.P. FOR THE SAMPLE, SLOW THE RATE OF HEATING TO 1-2 C/MIN. MEL-TEMP HEATING GUIDE USED TO ACHIEVE A HEATING RATE OF 1-2 C/MINUTE. FOR RAPID HEATING SET THE APPARATUS TO 1-2 UNITS HIGHER.

15 RECORDING AN ACCURATE MELTING POINT record the temperature range accompanying this change }2-3mm initial solid sintering solid first drops of liquid last crystals disappear liquid phase only solid phase only solid-liquid equilibrium

16 ANALYSE M.P. RANGE AND VALUE M.P. RANGE: PURE COMPOUNDS HAVE SHARP M.P. s NARROW M.P. RANGES. A RANGE OF 1-3 C IS CONSIDERED ACCEPTABLE. M.P. VALUE: THE M.P s OF PURE COMPOUNDS SHOULD NOT DIFFER DRASTICALLY FROM THE LITERATURE VALUES. A BROAD RANGE OR SIGNIFICANT DISCREPANCY FROM THE LITERATURE VALUE MAY MEAN THE M.P. FOR THE SAMPLE HAS TO BE REMEASURED.

17 COMPLETING EXPERIMENT 1 DON T FORGET TO ADD BOILING STONES TO ALL LIQUIDS BEING HEATED. THOROUGHLY CLEAN ALL GLASSWARE WITH ACETONE. HAND IN YOUR PRODUCT IN A LABELLED VIAL. A LAB REPORT IS DUE FOR THIS EXPERIMENT.