Practickles Flashcards
CP1 - molar volume of gas
gas syringe + lime water
key points:
- weak acid - to minimise gas loss
- lubricate plunger
issues:
- ensure bung is air tight (minimise gas loss)
- co2 can dissolve in water (effects volume)
CP 2 - Titration prep
key points:
- high molar mass (reduces weighing errors)
- ensure sample is pure and not air sensitive
CP 3 - Titration
key points:
- make sure to rinse pipette and calibrate
- phenophaelin returns to colourless when base reacts with CO2
issues:
- diluter solution (reduces percentage error)
- white tile (determines end point clearer)
CP 4 - Haloalkane hydrolysis
key points:
- water is the nucleophile
- reducing temp = reducing RoR (lower’s uncertainty)
- adding nitric acid removes any present carbonate ions
CP 5 - oxidising alcohol
method:
1. Add acidified KMNO4 to flask and place in ice water
2. Add anti-bg and ethanol then stir gently
3. Warm till RTP
4. Reflux and distil to collect -cooh product
Chlorination of methyl-2-propan-1-ol
- add conc HCl and tertiary alcohol - swirl
- Add rubber bung tightly and swirl (release occasionally to decrease pressure)
- Add anyhdrous CaCl2 and layers will form
- Release aqueous layer and add sodium hydrogen carbonate to remove unreacted HCl
- Run off the aqueous layer and place organic layer in flask and add drying agent
- Distil
Key points:
- weaker base prevents the hydrolysis of the haloalkane
CP 8 - enthalphy change (Hess’s law)
polystyrene cup practical
key points:
- extrapolate to find change in temp
- need to use2 enthalpies
errors:
- SHC of water used
CP 9 - Ka of [HA]
key issues:
- calibrate PH monitor with deionised water to remove ions attached to the bulb
issues:
- PH is to 2 dp (more precise)
- PH is quantitative (reduces subjectivity)
CP 10 - constructing electrochemical cells
method:
1) rub electrodes with sand paper to expose the surface area
2) soak saltbridge in KNO3
3)use a high resistance voltmeter
key points:
- standard conditions
- some substances are too dangerous to use at 1 mol dm -3
- inert gas to be used
errors:
- theoretical xx experimental if not in standard conditions
CP 11 - redox titration
method:
1. crush tablets and add a bit of H2SO4 to dissolve
2. filter and wash filter with distilled water
3. add filtrate to flask and fill up to the 250cm3 line with H2SO4 to dilute
key errors:
- washing (to ensure all Fe tablets are dissolved - increasing yield)
CP 12 - transition metal complexes
method:
1. weigh out a sample of copper sulfate and dissolve in H2O
2. add concentrated ammonia from the fume cupboard
3. vacuum filter + cold ethanol and then filter again
4. dry crystals in funnel for a while - add another filter paper on top to dry further
5. place in drying oven and compare mass
key errors:
if product is gained - impurites or wet crystals
if product is lost - some product remains in solution or reaction is incomplete
CP 13 - aspirin
method:
- add 2-hydroxybenzoic acid to pear flask
- add acetic anhydride and 8 drops of H3PO4
- warm mixture under reflux for 5 mins
- add deionised water and stand in flask of ice cold water
- filter under reduced pressure
- dissolve product in warm ethanol and add warm water
- dry and place in drying oven
- measure melting point
2-4 DNHP process
- filter orange precipitate
- dissolve in warm organic solvent
- filter and allow to recrystalise
- wash in cold organic solvent
- dry and determine melting point
- compare to data book value
wide range: impurities
the iodine rates reaction
- mix h2so4 and propanone (equal amounts and equal conc)
- add excess iodine to the reaction beaker and swirl - start timer
- at approx. 3 mins pippete 10cm3 of the reaction solution and add NaHCO3 (to quench reaction)
- Titrate sample with sodium thiosulfate and add starch indicater to find [I2]
- Repeat every 3 minutes
deep blue to yellow!
tha iodine clock :(
hydrogen peroxide + potassium iodide
- add starch indicator for an obvious colour change
reaction is too quick to time! so to improve accuracy:
- add sodium thiosulfate to delay the reaction (ADD FIRST WITH OTHER REACTANTS)
- once potassium iodide is added iodine ions will react with peroxide to form I2, however the I2 will react with the thiosulfate to reform the iodine ions
- once the thiosulfate runs out then solution will finally turn blue-black
