organic chemistry i chemistry 261academic.macewan.ca/saberim/261exp1.pdf · of benzoic acid. a...
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ORGANIC CHEMISTRY ICHEMISTRY 261
MACEWAN UNIVERSITYWinter 2016
LABORATORY INFORMATION
SAFETY
a. PERSONAL PROTECTIONb. LABORATORY ACTIVITIES
USING CHEMICALS
a. HANDLING/DISPENSINGb. SPILLINGc. DISPOSINGd. ACCIDENTS INVOLVING CHEMICALS
EQUIPMENT
a. LOCATIONb. GLASSWARE: BREAKAGES AND DISPOSAL
LAB EXPERIMENTS
a. PREPARATION: HAZARDOUS PROPERTIESb. DATA SHEETc. LAB REPORTd. QUIZZESe. EXTRA HELP
LABORATORY INFORMATION
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
EXPERIMENT 1: RECRYSTALLISATIONOF BENZOIC ACID
A PURIFICATION METHOD WHICH INVOLVES DISSOLVINGAN IMPURE SOLID IN A HOT SOLVENT AND THEN SLOWLY COOLING THE SOLUTION TO PROMOTE CRYSTALLISATION
OF THE PURIFIED SOLID.
REMOVAL OF IMPURITIES
SOLVENT CHOICE
THE SOLID SHOULD BE PRACTICALLY INSOLUBLE (OR SPARINGLY SOLUBLE) IN THE SOLVENT AT LOW
TEMPERATURES AND READILY SOLUBLE IN THE SOLVENT ATHIGH TEMPERATURES (CLOSE TO THE B.P. OF THE SOLVENT).
SOLUBILITY OF BENZOIC ACID IN WATER (100 mL)0.27g @ 17°C 6.8 g @ 95 ° C
IMPURITIES EITHER:
REMAIN INSOLUBLE AT ALL TEMPERATURES (REMOVEDBY FILTRATION, BEFORE RECRYSTALLISATION).
REMAIN SOLUBLE AT ALL TEMPERATURES (REMOVEDBY FILTRATION, AFTER RECRYSTALLISATION).
1. SETTING UP THE EXPERIMENT
HEAT D.I. WATER (TO BE USED AS THE RECRYSTALLISATION SOLVENT) IN A 125mL ERLENMEYER FLASK. YOU DON’TNEED TO WAIT FOR THIS TO BOIL BEFORE PROCEEDING.
ACCURATELY WEIGH 0.95-1.10g OF CRUDE BENZOIC ACID INTO A 50mL ERLENMEYER FLASK.
REMEMBER TO ADD BOILINGSTONES!
2. OBTAINING A SATURATED SOLUTION
DISSOLVE THE BENZOIC ACID IN THE MINIMUM AMOUNTOF BOILING WATER.
3. COMMENCING RECRYSTALLISATION
CAREFULLY REMOVE THE RECRYSTALLIZATION FLASK FROM THE HOTPLATE.
ALLOW THE FLASK TO COOLSLOWLY AND UNDISTURBEDTO ROOM TEMPERATURE.
COOL THE FLASK FURTHER BYPLACING IT IN AN ICE BATHFOR AN ADDITIONAL 10-15MINUTES.
4. ISOLATING THE CRYSTALS: VACUUM FILTRATION
SET UP THE APPARATUS FORVACUUM FILTRATION.
SWIRL THE CONTENTS OF THEERLENMEYER AND QUICKLYFILTER THE SLURRY.
WASH THE CRYSTALS WITH2 × 2mL PORTIONS OF ICE COLDWATER.
5. ISOLATING THE CRYSTALS: DRYING
ALLOW THE CRYSTALS TO DRY UNDER DYNAMIC VACUUM FOR~ 10 MINUTES.
TRANSFER THE CRYSTALS TOA LABELLED, PRE-WEIGHEDVIAL AND RECORD THE MASS.
RECORD THE MELTING POINTOF BOTH THE CRUDE AND PURIFIED BENZOIC ACID.
6. DETERMINING THE MELTING POINT
1. PREPARE SAMPLE BY CRUSHING TO A FINE POWDER.2. LOAD SAMPLE INTO CAPILLARY TUBE (2-3mm DEPTH).
3. HEAT SAMPLE FAIRLY RAPIDLY (~10°C/MINUTE) UNTIL 15-20°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.
STEPS IN DETERMINING AMELTING POINT
WHEN 15-20°C BELOW THE EXPECTED M.P. FOR THESAMPLE, 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 THEAPPARATUS TO 1-2 UNITS
HIGHER.
RECORDING AN ACCURATEMELTING POINT
}2-3mm
initialsolid
sinteringsolid
first dropsof liquid
last crystalsdisappear
liquid phaseonly
solid phaseonly
solid-liquidequilibrium
record the temperature rangeaccompanying this change
RECORDING AN ACCURATEMELTING POINT
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 THELITERATURE VALUES.
A BROAD RANGE OR SIGNIFICANT DISCREPANCYFROM THE LITERATURE VALUE MAY MEAN THE M.P. FOR THE SAMPLE HAS TO BE REMEASURED.
ANALYSE M.P. RANGE AND VALUE
COMPLETING EXPERIMENT 1
DON’T FORGET TO ADD BOILINGSTONES TO ALL LIQUIDS BEINGHEATED.
THOROUGHLY CLEAN ALL GLASSWARE WITH ACETONE.
HAND IN YOUR PRODUCT IN ALABELLED VIAL.
A LAB REPORT IS DUE FOR THISEXPERIMENT.