C#2.2 2022

C#2.2 2022

1. simple distillation

   • to obtain pure solvent from soluton
   • distillate: pure liquid collected from condenser
   • when solution is heated, X boils & turns into vapour. vapour condenses with help of condenser & is collected as distillate
   • bulb of thermometer placed near side arm leading to condenser - temp of hot vapour read accurately
   • boiling stones - smooth boiling of solution
   • water enters condenser at bottom to ensure that water jacket of water condenser is completely filled with cool water hence effective condensation
   • e.g. separating water from sea water / producing fermented liquor

2. fractional distillation

   • principle: difference in boiling points & liquids must be miscible
   • e.g. fractional distillation of crude oil to obtain petrol, diesel oil etc. / liquid air to obtain oxygen, nitrogen etc.
   • to separate miscible liquids with diff boiling points
   • miscible liquids - mix together to form uniform mixture
   • 3. process occurs many times & each time, vapour becomes progressively richer with liquid of lower boiling point
   • both liquids evaporate. X with lower boiling point evaporates faster and reaches top of column. Y with higher boiling point falls back into flask. X distills over at __°C and is collected as distillate. temp does not increase when X is distilling. temp increases after all X has distilled over, and until Y distills. new flask used to collect Y.
   • 1. fractionating column provides SA for multiple condensation of vapours and evaporation of liquids to separate miscible liquids
   • 2. as vapour travels up column, larger SA allows vapour to cool, condense into liquid, and revaporise as more heat reaches it
   • hot water bath - volatile mixture (boiling point close to room temp so evaporate easily at room temp)
     • volatile liquids e.g.: petrol, ethanol, perfume
   • oil bath - boiling point of component above 100°C

3. chromatography

   • separate solutes in complex mixture
   • indentify solutes in mixture
   • determine purity of substances
   • principles
     • diff substances have diff solubilities in solvent
     • diff substances have diff levels of affinity for filter paper
     • speed and distance by which solute separates dependent on solubility and adsorption (affinity) by chromatography paper
   • more soluble solute moves further. solute adsorbed to chromatography paper moves slower. with time, diff solutes separate at diff spots on chromatogram.
   • spots don't separate out = dye insoluble in solvent
   • descending method - help of gravity thus more effective. longer chromatogram needs to be used
   • starting line drawn in pencil. ink is mixture of dyes and may separate into components thus interfering with results.
   • allow solvent to run as far from starting line as possible for better separation
   • solvent level must be below spots marked on start line so that spots don't dissolve in solvent before start of experiment, meaning no separation is done
   • boiling tube/ beaker used must be covered to prevent evaporation of solvent (most organic solvents volatile)
   • e.g. separating dyes from inks, pigment in flowers or leaves, amino acids from proteins for analysis, testing for pesticide or chemical levels in food, urine analysis in sports
   • locating agent makes colourless spots visible by reacting with the dye to form a coloured substance

4. separating funnel

   • separating mixture of immiscible liquids
   • immiscible liquids - do not mix together to form uniform solution but form dfferent layers with denser liquid at bottom
   • e.g. separation of oil from water / chloroform from water
   • denser liquid sinks. when tap is opened, denser liquid is obtained. new beaker used to collect less dense liquid.
   • principle: difference in density

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