Practical Techniques Flashcards
Recrystillisation
-Dissolved in a minimum volume of hot solute
-solution filtered to remove impurities
-allow to cool
- filtering, washing and drying the pure crystals
Colorimetry
-Prepare standard solutions
-Use a suitable wavelength filter
-Use a blank
-Prepare calibration graph
Choosing solvent for recrystillisation
- Completely soluble at high temperatures and only sparingly soluble at lower temperatures
Choosing solvent for solvent extraction
Immiscible with water
Unreactive with the solute
Volatile
melting point
narrow range for pure sample, larger range from impure sample
Separating funnel
(solvent extraction)
-shake mixture
-leave mixture to separate into layers
-run off lower layer
What is recrystallization used to do?
Purify impure substances
What does heating under reflux allow?
allows a reaction mixture to be a heated for a long period of time without volatile substances escaping
What type of funnel is used during vacuum filtration?
Buchner funnel
How to maximise the quantity of solvent extracted?
Repeat the solvent extraction process
How can the identity of a pure compound be identified?
melting point analysis and a comparison with the literature value
How to do mixed melting point procedure
- Mix a small quantity of the product with some of the pure compound and determine the melting point
- If the melting point you’ve recorded is the same is the literature value, then the compound is pure
What is thin layer chromatography used for?
separate components present within a mixture
