instrumental analysis/practicals Flashcards
what is mass spectrometry used for?
determining the accurate GFM and structural features of an organic compound
how does mass spectrometry work?
- a small sample of an organic compound is bombarded by high-energy electrons, removing electrons from the molecule, which generates positively charged molecular ions known as parent ions
- these then break into smaller positively charged ion fragments and a mass spectrum is obtained
what is melting point analysis used for?
identifying the identity of a pure compound
what can determination of a compound’s melting point indicate?
its purity
- presence of impurities lowers the melting point and broadens its melting temperature range
what does determination of a mixed melting point involve?
mixing a small quantity of the product with some of the pure compound and determining the melting point
- this can be used to determine if the product and the pure compound are the same substance
what are back titrations used for and how is this done?
finding the number of moles of a substance by reacting it with an excess volume of a reactant of known concentration. the resulting mixture is titrated to work out the number of moles of reactant in excess, and from the initial number of moles of reactant, the moles used in the reaction can be determined
when are back titrations useful?
when trying to work out the quantity of a substance in a solid with low solubility
what is elemental microanalysis used for?
to determine the masses of C, H, O, S and N in a sample of an organic compound, in order to determine its empirical formula
how does elemental microanalysis work?
- sample is weighed accurately
- sample burned in pure oxygen from a cylinder
- gaseous products fed into a detector
- percentage of gaseous products calculated, experiment repeated
how is empirical formula calculated?
- take known mass of elements and divide by mass of one mole
- calculate ratio between elements by dividing above numbers by the smallest number
what is proton NMR spectroscopy used for?
can give info about the different chemical environments of hydrogen atoms in an organic molecule, and how many hydrogen atoms there are in each of the environments
what is gravimetric analysis used for?
determining the mass of an element or compound in a substance
what is heating to a constant mass used for?
removing all moisture from a substance which would increase the mass of the substance
what does a desiccator do?
prevents readsorption of water
how can conversion of a substance occur?
- when it undergoes a precipitation reaction to allow isolation and purification
- by volatilisation to allow isolation and purification
