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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.