10 - PURE ORGANIC SOLID PREPARATION AND PURITY

avatar
Created by
Jasmine Singh

Cards (15)

  • KEY STAGES IN PREPARATION OF AN ORGANIC SOLID?
    1. Reaction
    2. Filter under reduced pressure
    3. Purify solid by recrystallization
    4. Test product purity
  • REACTION?
    1. Weigh solid reagents by difference
    2. Transfer to reaction vessel
    3. Record precise mass
    4. Measure and add liquid reagents using appropriate glassware
    5. If required heat reaction vessel until reaction is complete
  • FILTER PRODUCT UNDER REDUCED PRESSURE?
    Use Buchner funnel
    • filter paper
    • vacuum pump
    • Buchner funnel
    • Buchner flask
    • filtrate
  • PURIFY SOLID BY RECRYSTALLISATION?
    1. Dissolve product in minimum of hot solvent (water/ ethanol)
    2. Stir if required
    3. Allow solution to cool (can use ice bath) until crystals of solid product form
    4. Filter off pure product under vacuum (using Buchner funnel)
    5. Place in desiccator for drying
    6. Accurately record mass of pure solid
  • TESTING PRODUCT PURITY?
    1. Place crushed solid sample into capillary tube
    2. Place capillary tube in melting point apparatus/ oil bath (Thiele tube)
    3. Heat sample
    4. Heat slowly near melting point
    5. Record melting temperature
    6. Compare value to data source value
  • PURPOSE OF MINIMUM VOLUME OF HOT SOLVENT?
    saturated solution and enable crystallisation on cooling
  • PURPOSE OF FILTERED HOT?
    remove insoluble impurities/ prevent crystals forming during filtration
  • PURPOSE OF COOLING IN ICE?
    increase number of crystals formed
  • PURPOSE OF WASHING WITH COLD WATER?
    remove soluble impurities (hot water would dissolve crystals)
  • WHY MAY YIELD NOT BE 100%?
    • impure salicylic acid
    • reaction did not go to completion
    • mass lost during purification
  • TWO OBSERVATIONS OF AN IMPURE SOLID BOILING'S POINT?
    • melting range too large
    • melt before true melting point
  • WHY MAY A PURE SAMPLE MELT AT A DIFFERENT POINT?
    temperature on thermometer not same as sample/ sample heats up at different rate than thermometer
  • HEATING UNDER REFLUX?

    • mixture of liquids heated to boiling point for prolonged period of time (using water bath if highly flammable)
    • vapour escapes from liquid mixture
    • cooled by condenser (do not seal top of condenser)
    • changes back to liquid returning to flask
  • DISTILLATION?
    • isolate impure product from rest of reaction mixture
    • impurities may be unreacted reagents, by-products or products as the result of side reactions/ catalysts
  • PURIFICATION (WASHING/ DRYING)?
    1. Transfer distillate to separating funnel
    2. Add 25 cm^3 Na2CO3
    3. Stopper funnel, invert several times (open stopper in between to release pressure)
    4. Allow two layers to separate
    5. Run off aqueous lower layer (waste)
    6. Add further 25 cm^3 of saturated CaCl2, repeat invert and run off
    7. Pour organic liquid into beaker
    8. Add anhydrous CaCl2 to dry
    9. Filtered/ distilled again to further purify and confirm purity by testing boiling point