chemistry - 3f - practical skills and techniques Flashcards
What does colorimetry use?
The relationship between colour intensity of a solution and the concentration of the coloured species present.
What is a colorimeter or a spectrophotometer used for?
To measure the
absorbance of light of a series of standard solutions, and this data is
used to plot a calibration graph.
How is the concentration of the solution being tested determined from?
Its absorbance and by referring to the calibration curve.
Where must the concentration of coloured species in the solution being tested lie?
In the straight line section of the calibration graph.
What is distillation used for?
Identification and purification of organic
compounds.
What is the boiling point of a compound, determined by distillation, one of?
The physical properties that can be used to confirm its identity.
How can distillation be used to purify a compound?
By separating it from less volatile substances in the mixture.
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 heading under reflux, where is the reaction mixture placed?
In a round-bottomed flask with anti-bumping granules and the flask is fitted with a condenser. The flask is then heated using an appropriate
source of heat.
What does vacuum filtration involve?
Carrying out a filtration under reduced pressure and provides a faster means of separating from a filtrate.
A Büchner, Hirsch or sintered glass funnel
can be used during vacuum filtration.
What can be used during vacuum filtration?
A Büchner, Hirsch or sintered glass funnel.
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.
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.
What happens in the separating funnel when carrying out a solvent extraction?
The two immiscible solvents
form two layers in the separating funnel. The solute dissolves in both
solvents and an equilibrium establishes between the two layers.
Solvent extraction: What is the ratio of solute dissolved in each layer determined by?
The equilibrium constant K.
Solvent extraction: What happens to the lower and upper layers?
The lower layer is run off into a container and the upper layer is poured into a second container. This process is repeated to
maximise the quantity of solute extracted.
Solvent extraction: When is the quantity of solute extracted greater?
If a number of extractions
using smaller volumes of solvent are carried out rather than a single
extraction using a large volume of solvent.
Solvent extraction: What should the solvent used be?
- immiscible with the liquid mixture or solution (usually water)
- one in which the solute is more soluble in than the liquid mixture or solution (usually water)
- volatile to allow the solute to be obtained by evaporation of the
solvent - unreactive with the solute
