core practical 13: iodine clock reaction Flashcards
(14 cards)
propanone reacting with iodine consideration
ACIDIC SOLUTION. (sulphuric acid catalyst)
method
- add known vol and conc propanone and sulfuric acid to a beaker
- add iodine and swirl. immediately start stopclock
- use 10cm3 pipette to withdraw sample of mixture and transfer to conical flask containing sodium hydrogen carbonate (quenches reaction by neutralising acid)
- record time whenHALF contents pipette added
- titrate against sodium thiosulphate. add starch indicator when colour is pale yellow. END POINT IS BLUE TO COLOURLESS
- repeat every 2-3 mins
processing results
-plot graph of time against vol titre of sodium thiosulphate- its PORPOTIONAL to conc of iodine , so can give u results
- propanone and acid are in large excess so concentrations are constant
order with respect to iodine
0
straight line through the origin
factor having effect on rate
-temperature
- carry out in a water bath
why time when pipette half empty
- mean time the reaction was quenched, as doesnt empty all reaction mixture in one go
order w respect to hydrogen ions
first
why does it allow for rate wrt i2 to be calculated
- propanone and acid are in large excess
- concentrations dont change during reaction
describe the reaction
- remoev small samples with a volumetric pipette
- QUENCH WITH SODIUM HYDROGEN CARBONATE TO NEUTRALISE ACID CATALYST
- sample with sodium thiosulphate with starch catalyst
thiosulfate ion
S2O3 2-
equation of reaction
CH3COCH3 + I2 = CH3COCH2I + H+ + I-
why are there in theory 2x h+ produced
- 1 is the catalyst being regenrated
- 1 is removed from the propanone; is a product of the reaction
rate equation
rate =. k [propanone][h+]
thiosulfate + iodine
2s2o3 2- + i2 = 2i- + s4o6 2-
