Required Practicals 2026 Organic

rp10c - melting point

• solid organic compound in capillary tube, slowly heat with solvent surrounding tube (solvent higher b.p. than compound)

• note temperature melting begins and ends - repeat calc. mean

• capillary tubes thin glass - fairly confident temp. inside tube matches temp. on thermometer

• pure - sharp melting point

• impure - lower mp, over range of temps. if an organic liquid - higher bp over a range

• impurities - solvent used (press between filter paper to remove)

• pure crystals are larger and white

rp 10d - organic liquid

• layers form because organic liquid is immiscible (doesn’t mix with water, hydrophobic/insoluble - no H bonds, long carbon chain)

• layer at top lower density (organic), layer at high density (aqueous)

• run off aqueous layer into conical flask, collect organic in a diff. conical flask

• wash organic layer with Na₂CO₃ to neutralise acid catalyst - produces CO2

• invert funnel and open tap, repeat - CO2 rises and leaves, prevents buildup of pressure

• if organic layer still contains water - drying agent, anhydrous CaCl2/MgSO4

  • if water present CaCl2 clumps together and sinks. dry - floats gently, slowly to bottom

  • both MgSO4 and CaCl2 are suitable because they absorb water well and are insoluble and inert in organic liquids

• remove drying agent with vacuum filtration - organic liquid at bottom

rp 10a: preparation of an organic solid

• weigh by difference method

• ethanoic anhydride reaction less vigorous

• acid catalyst (making an ester) phosphoric acid corrosive

• heat on hot plate for 20 mins

• add to ice bath to encourage crystallisation, higher yield + faster

• filter under reduced pressure to remove aspirin solid

• leave crystals warm to dry

• weight and calculate yield - further purification

rp10 b: recrystallisation

• dissolve crude product in minimum vol of hot solvent - saturated solution, ensures high yield - crystals will form on cooling

  • suitable solvent - highly soluble at high temp. low soluble at low temp. - impurities still soluble at low temp.

• filter whilst hot to remove insoluble impurities before crystals form (gravity filter)

• leave to cool - increases yield - soluble impurities stay dissolved

• filter under reduced pressure - wash with cold solvent to remove soluble impurities stuck to crystals

• test purity with mp and calculate yield

• yield not 100% - product left in glassware <100%, sample wet when weighing >100%

vacuum filtration

• faster than gravity filtration, improved separation of fine particles

• more efficient, continuous filtration

• air drawn through filter funnel and pulls liquid down

• wash solid with cold solvent

• compress crystals - ensures air passes through crystals rather than around - better drying

rp7: initial monitoring

• assume conc. of iodine is proportional to iodine

• add H2O2 to iodide ions in acidic conditions with starch and limited thiosulfate ions

• H2O2 produces iodine, which reacts with thiosulfate to reform iodide until thiosulfate is used up - when it is blue black colour forms

• time taken for mixture to turn blue is recorded

• repeat with diff concentrations of iodide

• plot graph 1/t against conc. - shape of curve

rp7: continuous monitoring

• Measure 50 cm3 of the 1.0 mol dm–3hydrochloric acid and add to conical flask.

• Set up the gas syringe in the stand

• Weigh 0.20 g of magnesium

• Add the magnesium ribbon to the conical flask, place the bung firmly into the top of the flask and start the timer

• Record the volume of hydrogen gas collected every 15 seconds for 3 minutes

  • gas syringes usually only measure up to 100cm3

  • measuring initial rate is preferrable because we know conc. at start

other ways to monitor reaction:

• electrical conductivity (if there is a change in ions)

• optical activity (followed with a polarimeter)

• measure change in mass

• take samples and titrate

• propanone + iodine - take at 5 min

• quench with sodium hydrogencarbonate - titrate against thiosulfate

• iodine colour fades to straw yellow - add starch, goes blue black

• add more thiosulfate until colourless

• repeat every 5 mins for 30 mins