Redox Titrations Flashcards
Colour change of potassium permanganate(VII) when reduced
From purple when 7+ to pink when Mn2+
Colour change of Fe2+ when oxidised
Very pale green when Fe2+ to very pale yellow when 3+
Equation for reaction between Fe2+ and MnO4 -
5Fe2+ + MnO4 - + 8H+ —> 5Fe3+ + Mn2+ + 4H2O
What occurs at end point when MnO4- added to Fe2+
When all Fe2+ used up there is excess MnO4 - so colourless (very pale pink)
What happens if insufficient acid added to Fe2+ and MnO4- titration
Titre value higher and brown precipitate of MnO2 forms so MnO4- not fully reduced
Equation for reaction between MnO4- and C2O42-
2MnO4- + 16H+ + 5C2O42- —> 2Mn2+ + 8H2O + 10CO2
Why is reaction between MnO4- and C2O42- slow
As two negative ions so repel each other meaning high activation energy
Colour change with indicator in iodine thiosulfate reaction
From blue black to colourless
Colour change without indicator between thiosulfate and iodine
From brown(if not dilute)/yellow(if diluted) to colourless
Why shouldn’t you add starch immediately to iodine
As forms complex with iodine, must add some of the sodium thiosulfate before adding the starch
What can reaction between thiosulfate and iodine be used to work out
To work out concen of an oxidising agent, work out the amount of iodine left over using sodium thiosulfate
Colour change when MnO4- to Mn2+
From pink to colourless
