Question

If we are doing an Iodine test and the solution in the test tube we are working with has two solution inside, being (1) starch (2) gelatin. If we add the Iodine solution to it, will it change color (positive reaction)? and Why.

Answer 1

When iodine is added to starch, the colour will change to blue/ black showing positive result and when iodine is added to gelatin,the colour will not change and remain as such showing negative result.

Explanation- Iodine test is used to test the presence of starch. Starch turns into an intense blue black colour upon addition of aquous solutions of the iodine i.e; triiodide anion. In the absence of the starch,the colour of the supplied solution reamains unchanged. The blue black colour is due to the presence of amylose in starch. The iodine molecule slips inside of the amylose coil. This makes a linear triiodide ion complex soluble that slips into the coil of the starch causing an intense blue-black colour. Gelatin tested negative because it is a mixture of peptides and proteins. Due to absence of amylose and starch the test is negative.