secret 發問於 科學及數學化學 · 1 十年前

about f.6 chp.3 chemical equations and stoichiometry thz

in this chapter


titrations involving idine which is a mild oxidizing agent are offen called

"iodometric titrations"

starch solutionis is used indicator to signal the end point of the titration

when the brown colour of iodine fades as the end point approaches, a little

amout of starch solution is added.

the Q is

why don't we added the starch solution in the iodine solution,,and need to

added it when the brown colour of iodine change to pale yellow??

please explain it longer and use english


1 個解答

  • 1 十年前

    The starch solution is act as the indicator.At the end point it is difficult to obserb when the colour change from pale yellow to colourless.SO starch solution is adder which clearly show the end point from dark blue to colourless.because starch can form a bule complex with iodine.

    it is need added it when the brown colour of iodine change to pale yellow because when the concentration of iodine is high. the starch will form an irreversible blue complex with iodine can release form the it must be added when the iodine containing solution when it is pale yellow (the concentation of iodine is low)


    資料來源: myself