reaction types Flashcards
Procedure of a standard solution:
Accurately weigh out the mass of solute by weighing by difference, transfer the solute into a beaker and add deionised water to dissolve the solute. Then pour the mixture into a standard flask, using a funnel. Then rinse the beaker and funnel with deionised water, using a pipette make the solution up to the graduation mark with deionised water, then invert the flask several times.
Gravimetric analysis
Heating a substance to constant mass
— allowing to cool in a desiccator to prevent absorption of water
— weighing by difference
— repeating the steps of heating, cooling and weighing until no further changes in mass are observed
Volumetric analysis
preparing a standard solution
accurate dilution
standardising solutions to determine accurate concentration
titrating to obtain concordancy using burettes, pipettes and volumetric flasks
choosing an appropriate indicator
Chromatography tlc
Thin-layer chromatography (TLC) uses 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.
Mixed melting point determination
involves mixing a small quantity of the product with some of the pure compound (50% each) and determining the melting point. If the melting point turns out to be sharp and close to the expected value, then the two substances must be identical. If the two substances are not similar, then the melting point of the mixture will be much lower and the melting range much broader.
Recrystillisation
Dissolve the impure crystals in the minimum volume of hot solvent
Filter the hot solution to remove any insoluble impurities
Allow the solution to cool and crystallize
Filter off the crystals using vacuum filtration and wash with cold solvent
Allow the crystals to dry in the oven and then cool in a dessciator
The solvent for recrystallization is chosen so that the compound being purified is completely soluble at high temperatures and only sparingly soluble at low temperatures
a substitution reaction is
in which an atom or group of atoms is replaced by another group of atoms
an addition reaction is
a reaction in which two molecules join together to make one larger molecule
an elimination reaction is
one in which a small molecule is removed from an organic compound
colorimetry
A colorimeter consists essentially of a light source, a coloured filter, a light detector and a recorder. The filter colour is chosen as the complementary colour to that of the solution resulting in maximum absorbance. The light passes through the filter and then through the coloured solution and the difference in absorbance between the coloured solution and water is detected and noted as an absorbance value.
The second stage is to determine the concentration of a sample of the decamethylcobaltocene solution.
The absorbance/transmittance of the unknown is measured
Desrcrube a back titrations
A back titration allows the concentration of an unknown solution to be determined by reacting it with a no in excess of a reagent. The quantity of the excess Regent is the term and by titration with a second Regent.
A back titration is used for substances that or not a primary standard, therefore a standard solution cannot be prepared
How to prepare a calibration graph
Choose an appropriate filter (complimentary colour)
Standard solutions of different concentrations are prepared
Blank or solvent only measurement is taken
Measure the absorbance of the standard solutions and from these plot the calibration graph
Explain how proton nmr spectroscopy works
Nuclei of atoms behave like tiny magnets and in a strong magnetic field some align with the field (lower energy) whilst the rest align against it (higher energy). The absorption of radiation in the radio frequency of the electromagnetic spectrum causes the 1h nuclei to flip from the lower to higher energy alignment. As they fall back from higher to lower energy alignment emitted radiation is detected and plotted on a spectrum
Why d-orbitals in a transition metal are no longer degenerate
In transition metal complexes the ligands approach the central metal ion along the x/y/z axis. The electrons in the d-orbitals. If the metal ions are repelled by the electrons of the approaching ligands, their d-orbitals therefore have higher energy than the d-orbitals that lie between axes. The d-orbitals are no longer degenerate. This is known as the splitting of d-orbitals.
order of spec series:
I-,cl-, F-, OH-, h20,nh3,cn-
What is a ligand
Ligands are negative ions with one or more lone pairs of electrons that they can donate to the central metal ion, forming dative covalent bonds.
