unit 4 - how to pass: practical skills and techniques Flashcards
What is a desiccator used for?
To store dried samples in a dry atmosphere.
What does vacuum filtration involve?
Filtration under reduced pressure and provides a faster means of separating a precipitate from a filtrate.
What can be used during vacuum filtration?
A Buchner, Hirsch or sintered glass funnel.
What does heating under reflux allow?
Heat energy to be applied to a chemical reaction mixture over an extended period of time without volatile substances escaping.
When carrying out heating under reflux, where is the reaction mixture usually placed?
In a round-bottomed flask with anti-bumping granules and the flask is fitted with a condenser.
What is distillation?
A technique used to purify, by separating it from less volatile substances in the mixture, and identify organic compounds.
What does solvent extraction involve?
Isolating a solute from a liquid mixture or solution by extraction using an immiscible solvent in which the solute is soluble. The quantity of solute extracted is greater using a number of extractions with smaller volumes of solute compared to a single extraction with a large volume of solute.
What is recrystallisation used for?
To purify an impure solid.
How is the solvent for recrystallisation chosen?
So that the compound being purified is completely soluble at high temperatures and only sparingly soluble at lower temperatures.
How can a pure compound be identified?
By melting point analysis with reference to the literature melting point value.
What can determining the melting point of a compound give an indication of?
How pure a compound is.
What does the presence of impurities in the compound cause?
Lowering of the melting point and broadens its melting temperature range due to the disruption in intermolecular bonding in the crystal lattice.
What does determination of a mixed melting point involve?
Mixing a quantity of the product with the pure compound and determining the melting point range. The melting point value and the range of the melting temperature is used to determine whether the product and the pure compound are the same substance.
