prac Flashcards
titration table
titration number
final burette reading /cm3
initial burette reading /cm3
volume of ____ used /cm3
values used (tick)
comment on consistency of results
As titration 1 and 2’s readings are within 0.10cm3 of each other, the readings are consistent. As there were no anomalous results, a third titration was not attempted
explain presence or absence of anomalous results
Consistent readings were obtained as proper pipetting and titration techniques were adopted. The titrant from the burette was added drop wise nearing the end of the titration to ensure the latter was not exceeded. Also swirling of the conical flask was done continuously during the titration to ensure even mixing of the reaction mixture
small or large titre value problems
small - large percentage uncertainty, affecting accuracy
large - titration is tedious and time consuming as careful refilling of the burette has to be done
why cannot measure NaOH through direct weighing
NaOH is hygroscopic and mass cannot be determined for the prep of standard solution
it will also react with co2 in the air to give carbonate which will add to the mass
using funnel on conical flask
the reaction produces effervescence of CO2 which may cause splashing of the reaction mixture. the funnel makes the opening of the conical flask smaller so that the loss of _____ out of the conical flask due to acid spray is reduced
why weighing bottle needs to be resigned after fa1 is added to a conical flask
some solid FA1 may remain in the emptied weighing bottle. receiving the emptied weighing bottle allows for the actual mass of fa1 that is added to the conical flask to be determined
why can’t iodine be left standing
some iodine will vaporise if the solution of iodine is left standing. due to the vaporisation of iodine, the titre value would be lower than the actual reading
why cannot add starch indicator at the start of the titration
at the start, concentration of iodine is relatively high. if starch is added at the start, many iodine molecules will be trapped in the starch molecules since the liberation of iodine molecules from the starch molecules take time and the titration will be inaccurate
why don’t need precise instruments
______ is added in excess and is not the limiting reagent hence precision of the apparatus used us irrelevant
how an incorrect sample will affect titre value
the CONCENTRATION of ______ in the incorrect sample will be higher/lower than the intended value _______
John said using measuring cylinder underused of pipette will not affect results thoughts and opinions
no. KIO3 in fa1 is the limiting reagent in the reaction mixture. hence the precision of the apparatus used would affect the accuracy of the volume of fa3 measured and hence would affect the amount of iodine produced for titration. the latter would in turn affect the accuracy of the titre volume.
why solution in conical flask turn blue after being left for some time
under acidic conditions, atmospheric oxygen can oxidise some of the iodine ions in the conical flask back to iodine. the iodine produced reacts with the starch indicator present and a starch iodine complex is formed which causes the solution to turn blue again
end points indicator colours heehee
methyl orange (3.2 - 4.4) red orange yellow
screened methyl orange (3.2 - 4.4) violet grey green
thymol blue (8 - 9.6) yellow green blue
thymolphtalein (9.4 - 10.6) colourless blue/colourless blue
