reaction equation: schultz's & I/KI soln starch cellulose

[Ocean Breeze]

its yr 12 chemistry doing testing for cellulose, starch etc

The dark blue positive with schultz's soln on cellulose, and the Iodine /KI solution black positive on starch. Can anyone provide the reaction equation for these please?

Thanking you

[DavidPeterson]

Do you make your own Schulz solution or do you purchase it? I have been asked for this over the years, and the formulation I found on the 'net never seems to give positive results.

With respect to the starch / Iodine reaction: the best anyone (including Dr Karl Kruszelnicki) has ever been able tyo tell me is that a starch-iodine complex is formed.

[Graham Kemp]

Yeap. That's basically all it is to it.

Starch forms a tightly coiled spring in solution (almost torus-, or donut-, shaped).

The linear triiodide ion ( I₃- ) slips neatly into this coil to form an ionic complex; in which position its vibrations are constrained. Thus causing its change in absorbance ( a colour change ).

[Ocean Breeze]

Thanks Graeme. Perfect Just what I needed

David, I make my own schultz
Zn Cl sat soln then cooled.
The add drop by drop the I/KI soln

[DavidPeterson]

Yeap. That's basically all it is to it.

Starch forms a tightly coiled spring in solution (almost torus-, or donut-, shaped).

The linear triiodide ion ( I₃- ) slips neatly into this coil to form an ionic complex; in which position its vibrations are constrained. Thus causing its change in absorbance ( a colour change ).

Thanks for the description of the mechanism...it's something that I have asked many people over the years. Should have contacted my universtity organic chem lecturer (I think he's still alive...)