Preparation And Purification Of Organic Compounds Topic 18 SP 22

Many organic compounds are flammable so a naked flame might cause explosions Safer using a water bath

Provides nucleation sites for bubbles Prevents sudden violent boiling(bumping)

Allows for even heat distribution and reduces risk of cracking

Cold water in Leibig Condenser allows for evaporation of hot substances so vapours cool and condense back into liquid This prevents loss of volatile products and liquids

To prevent pressure build up and reduce risk of explosion

Ensure the entire jacket fills with water If it wasn’t fully filled/entered the top than the condenser would not be full and the vapours might not cool as quickly so some product might escape so yield is reduced

To separate substances with different boiling points

Aldehydes have a lower boiling point than alcohols So aldehyde can be collected by aldehyde vapour being condensed into a liquid and collected in a beaker

Used to separate substances with high boiling points or decompose when heated And used to separate products immiscible with water(such as oil)

Heat organic mixture(contains water and a product immiscible with water e.g oil) using water bath Steam is passed through mixture and pushes mixture through condenser Both water and organic product vaporise and collect distillate

1)Add products from distillation into a separating funnel 2)Add water to dissolve soluble impurities and let it settle 3)Top layer is impure product Bottom layer is aqueous layer 4) Remove stopper from separating funnel to remove aqueous layer

Purification by washing Purification by drying(removing water)

1)Use a liquid(Water or Sodium hydrogencarbonate for CAs) and add to our sample 2) impurities(such as salt when Na2CO3 reacts with CA) dissolve in washing solution so dissolve in aqueous solution Organic solution in top layer does not change so organic solution is purified

1) Take impure product from separating funnel and add to round bottom flask 2) Add anhydrous Calcium chloride(drying agent) removes aqueous substances still remaining 3) Invert flask and shake and leave for 20 mins 4) Filter out solid drying agent

Seperation solids from liquids and the liquid part is the desired part of using this apparatus

Place funnel over a beaker Add fluted filter paper on funnel and dampen Pour reaction mixture slowly Liquid is collected in beaker Solid is left behind on paper to be disposed

VF seperates liquids and solids 1) Place filter paper disc into the Buchner Funnel and dampen slightly to make a seal 2)Pour reaction mixture into the Buchner funnel 3)Vacuum creates a reduced pressure in the flask and pulls liquid through Solid is left in the funnel and can be recrystallised

1) Add minimum amount of hot solvent(solvent choice is important) for the impure solid to dissolve 2) Warm filter paper and funnel in oven 3) filter solution while still warm using gravity filtration 4) allow filtrate to cool and crystallise 5) filter crystals 6) rinse crystals with small amount of ice cold ethanol 7) dry crystals

So solution doesn’t cool down To prevent premature crystallisation occuring Which could reduce yield

Filtrate to cool: Product less soluble in cooler solvent so it crystallises out Solubilities remain dissolved Filter under reduced pressure: Removes soluble impurities producing a drier product

Set up distillation and calculate the temperature using a thermometer at which the product distillates off(boiling point) Compare this with value in data booklet If it has impurities: Boiling point is higher than what was recorded in DB Your sample boils over a range of temperatures

1) add sample of solid in capillary tube and place in heating element 2) slowly increase temperature until substance starts to melt 3) calculate temperature range 4) compare your melting point value to the data booklet value 5) impurities means lower melting point and higher range