used to find out conc of a chemical that's strong enough to oxidise iodine to iodide ions. The iodine is treates with thiosulphate ions, with starch as an indicator.
1 of 3
part 1
chlorate ions are strong enough to reduce iodine.
pour chlorate solution into a beaker
rinse a volumetric pipette (ensures pipette is clean and solution hasnt been diluted)
transfer a 25cm3 aliquot of solutin into a conical flask using a volumetric pipette and filler
add excess iodide ions by using a measuring cylinder to transfer 15cm3 of o.5M potassium iodide to the conical flask
add excess hydrogen ions by using a measuring cylinder to transfer 20cm3 of 1M sulfuric acid
contents will be brown because of amount of iodine made
2 of 3
part 2
titrate the iodine made with sodium thiosulfate to work out he number of moles of iodine in the first part
wash a burette with water, and then with a standard solution of sodium thiosulfte solution
fill burette with sodium thiosulfate
put conical flask on white tile
record initial burette reading to the nearest 0.05cm3
start rough titration, pale straw colour near end point .
at this point, add a few drops of starch, contents will be blue/black
end point is colourless
record the final burette reading and calculate rough titre by subtraction
wash conical flask with distilled water
carry out accurate titration, run sodium thiosulfate solution into conical flask until 1cm3 below rough titre
add dropwise
continue until results are concordant - within 0.1 cm3 of each other
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