Researching Chemistry Flashcards
What is stoichiometry?
Stoichiometry is the study of mole relationships involved in chemical reactions.
What is gravimetric analysis
Gravimetric analysis is used to determine the mass of an element or compound in a
substance. The substance is converted into another substance of known chemical composition, which can be readily isolated and purified.
What is precipitation conversion?
the substance undergoes a precipitation reaction. The precipitate is separated from the filtrate and the filtrate tested to ensure the reaction has gone to completion. The precipitate is washed, dried to constant mass and then weighed.
What is volatilisation conversion?
In volatilisation conversion the substance is heated and any volatile products (often water) are evaporated. The substance is heated to constant mass and the final mass recorded.
What qualities does a primary standard need?
♦ be available in a high state of purity
♦ be stable when solid and in solution
♦ be soluble
♦ have a reasonably high GFM
What is a complexometric titration?
complexometric titrations based on reactions in which complexes are formed — EDTA is an important complexometric reagent and can be used to determine the
concentration of metal ions in solution
What is colorimetry
uses the relationship between colour intensity of a solution and the
concentration of the coloured species present
What is distillation? What can it determine? Can it purify?
Distillation is used for
identification and purification of organic compounds.
The boiling point of a compound, determined by distillation, is one of the physical properties that can be used to confirm its identity.
Distillation can be used to purify a compound by separating it from less volatile substances
in the mixture.
What is heating under reflux?
Heating under reflux allows heat energy to be applied to a chemical reaction mixture over an extended period of time without volatile substances escaping.
How is heating under reflux carried out?
When carrying out heating under reflux, the reaction mixture is 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 is vacuum filtration?
Vacuum filtration involves carrying out a filtration under reduced pressure and provides a faster means of separating a precipitate from a filtrate. A Büchner, Hirsch or sintered glass funnel can be used during vacuum filtration
Recrystallisation technique
♦ dissolving an impure solid gently in a minimum volume of a hot solvent
♦ hot filtration of the resulting mixture to remove any insoluble impurities
♦ cooling the filtrate slowly to allow crystals of the pure compound to form, leaving
soluble impurities dissolved in the solvent
♦ filtering, washing and drying the pure crystals
How is the solvent for recrystallisation chosen?
The solvent for recrystallisation is chosen so that the compound being purified is
completely soluble at high temperatures and only sparingly soluble at lower temperatures.
What is solvent extraction?
Solvent extraction involves isolating a solute from a liquid mixture or solution by extraction using an
immiscible solvent in which the solute is soluble.
How is solvent extraction carried out?
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. The ratio of solute dissolved in each layer is determined by the
equilibrium constant, K . 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.
Determination of the melting point of a compound can give an indication of…
The purity of a compound
What does the presence of impurities do to the mp of a 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 is determination of mixed melting point?
Determination of a mixed melting point involves mixing a small quantity of the product with some of the pure compound and determining the melting point. The melting point value and the range of the melting temperature can be used to determine if the product and the pure compound are the same substance.
What is thin layer chromatography?
a technique used to separate the components present within a mixture.
Chromatography separates substances by making use of differences in their polarity or molecular size.
TLC technique
a fine film of silica or aluminium oxide spread over glass, aluminium foil or plastic. A small sample of the mixture being tested is spotted onto the base (pencil) line of the chromatogram. A solvent dissolves the compounds in the spot and carries the compounds up the chromatogram. How far the compounds are carried depends on how soluble the compounds are in the chosen solvent and how well they adhere to the plate. A developing agent or ultraviolet light is normally required to visualise
the spots on the chromatogram.
Rf
distance travelled by the sample R/
distance travelled by the solvent
