practical skills and techniques Flashcards
what is colorimetry
a technique that uses the relationship between colour intensity of a solution and the concentration of the coloured species present
how is the concentration of the solution being tested determined in colorimetry
from its absorbance and by referring to the calibration curve
where must the concentration of colored special in the solution lie in the calibration graph
the straight line section
what is distillation
technique used for identitfication and purification of organic compounds
what is one of the physical properties of a compound that can be used to confirm its identity in distillation
boiling point
how can distillation purify a compound
by separating it from less volatile substances in the mixture
what is heating under reflux
this allows heat energy to be applied to a chemical reaction mixture over an extended period of time without volatile substances escaping
how do you carry out heating under reflux
- reaction mixture is placed in a round bottomed flask with anti bumping granules
- flask fitted with a condensor
- flask heated using an appropriate source of heat
what does vacuum filtration involve
carrying out a titration in reduced pressure and provides a faster means of separating a precipitate from a filtrate
what can be used during vacuum filtration
- sintered glass funnel
- buchner
- hirsch
describe the process of recrystallisation
- dissolve an impure solid gently in a minimum volume of hot solvent
- hot filtration of the resulting mixture to remove any insoluble impurities
- cool the filtrate slowly to allow the crystals of the pure compound to form
- leave soluble impurities dissolved in the solvent
- filter wash an dry the pure crystals
how is the solvent for recrystallisation chosen
so that the compound being purified is completely soluble at high temperatures and only sparingly soluble at low 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 is the process of solvent extraction
- two immiscible solvents form layers in the separating funnel
- the solute dissolves in both solvents and an equilibrium establishes between the two layers
- the ratio of solute dissolved in each layer is determined by the equilibrium constant, K
- lower layer is run off into a container and the upper layer is poured into a second container
- process repeated to maximise the qunatity of solute extracted
how can the quantity of solvent extracted by maximised
using smaller volumes of solvent in a number of extractions rather than a single extraction using a large volume of solvent
