Practical

• shake mixture and leave to settle in the separating funnel • open the tap to separate the layers

• anhydrous magnesium sulfate (MgSO4) • anhydrous calcium chloride (CaCl2)

• place spots of controls on TLC plate • place a spot of the reaction mixture at regular intervals alongside controls • compare Rf values

• solution of reactant • solution of product

prevent evaporation of reactants or products OR ensure complete reaction (check with Ed)

• separate layers with a separating funnel • add drying agent to the organic layer (to remove any traces of water) • redistill collecting product at the desired product’s boiling point (to separate any organic substances)

• completely dissolve the solid in the minimum volume of hot solvent • cool the solution in an ice bath (scratch bottom of beaker with stirring rod to encourage crystal growth) • filter under reduced pressure • rinse filtrate (organic solid in buchner flask) with cool solvent • allow the organic solid to dry

• range must be greater than that of pure • melting/boiling point must be lower than the pure one (highest temp of impure lower than lowest temp of pure)

• organic solid crystallises as it is only soluble in hot solvent • impurities stay in solution as they are soluble in the hot and cool solvent

• impurities must be more soluble in the solvent than the organic product • e.g. if the impurities are non-polar and the organic product is polar, use a non-polar solvent so the organic solid only dissolves at high temperatures

• there may not be a known Rf value for some molecules • similar molecules may have similar Rf values • molecules usually shows smudges rather than clear dots

process by which the solid silica holds the different substances in the mixture to its surface

relative absorptions of substances with the stationary phase

separating an identifying volatile organic compounds

high boiling liquid or solid adsorbed onto an inert solid support

inert carrier gas such as helium or neon

• separated by solubility if stationary phase is liquid • separated by adsorption if stationary phase is solid

• each compound spends a different length of time dissolved in the liquid stationary phase • each compound reaches the detector at different times • the compound retained in the column for the shortest time has the lowest retention time and is detected first (least soluble)

time taken for each component to travel through the column in gas chromatography

• retention times are used to identify compounds present by comparing them to known retention times in data books • peak integrations determine the concentrations of components in the sample

• make standard solutions of known concentrations of the compound • gas chromatograms must be obtained for each standard solution • plot a calibration curve of peak area against concentration • use the calibration curve to measure the unknown concentration of the compound

• add silver nitrate and ethanol • warm to 50°C in a water bath • chloroalkane: white ppt • bromoalkane: cream ppt • iodoalkane: yellow ppt

• pH indicator paper (weak acid) • won’t react with Na2CO3 • mix with bromine water and it decolorises it (from orange colour) • undergoes electrophilic substitution reaction with bromine at room temperature