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
what criteria does a solvent used in solvent extraction need to meet
- immiscible with the liquid mixture or solution
- 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 solvent
what is the melting point
the temperature range over which the solid first starts to melt, to whwen all of the solid has melted
how can the identity of a pure compound be confirmed in relation to MP
melting point analysis and a comparison of the experimentally determined melting point with a literature or known melting point value
what does determination of the melting point of a compound give an indication of
the purity of the compound
the presence of impurities in the compound lowers 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 small qunatity of the product with some of the pure compound and determining the melting point
the melting point value and the range of melting temperature can be used to determine if the product and the pure compound are the same substance
