Why does lugol iodine react with starch?

Lugol's Iodine (IKI) test for the presence of starch: Iodine dissolved in an aqueous solution of potassium iodide - reacts with starch producing a deep blue-black color. This reaction is the result of the formation of polyiodide chains from the reaction of starch and iodine.
A.

How does iodine react with starch?

Starch consists of two types of molecules, amylose - a soluble starch and amylopectin. When starch is mixed with iodine in water, an intensely blue colored starch/iodine complex is formed. Many of the details of the reaction are still unknown. Apparently, the Iodine gets stuck in the coils of beta amylose molecules.
  • What is the iodine test?

    Iodine Test. Using iodine to test for the presence of starch is a common experiment. A solution of iodine (I2) and potassium iodide (KI) in water has a light orange-brown color. If it is added to a sample that contains starch, such as the bread pictured above, the color changes to a deep blue.
  • What is soluble starch solution?

    Because of this starch is usually made up as a percentage solution rather as a molar strength. In general, starch is insoluble in water, but some types of starch eg., soluble starch or corn starch will dissolve in water provided they are made into a paste first with cold water then dissolved in boiling water.
  • What is the meaning of iodine solution?

    Lugol's iodine, also known as aqueous iodine and strong iodine solution, is a solution of potassium iodide with iodine in water. Taken by mouth it is used to treat thyrotoxicosis until surgery can be carried out, protect the thyroid gland from radioactive iodine, and to treat iodine deficiency.
B.

What happens when you add iodine to starch?

color in the presence of iodine. The triiodide ion ion slips into the coil of the starch causing an intense blue-black color. Starch Test: Add Iodine-KI reagent to a solution or directly on a potato or other materials such as bread, crackers, or flour. A blue-black color results if starch is present.
  • Why do all monosaccharides but only some disaccharides react?

    All monosaccharides are reducing sugars; they all have a free reactive carbonyl (C=O) groups. Some disaccharides have exposed carbonyl groups and are also reducing sugars. Other disaccharides, such as sucrose, are non-reducing sugars and will not react with Benedict's solution.
  • What is the color of starch?

    Starch Test: Add Iodine-KI reagent to a solution or directly on a potato or other materials such as bread, crackers, or flour. A blue-black color results if starch is present. If starch amylose is not present, then the color will stay orange or yellow.
  • What does starch test for?

    Starch Test: Add Iodine-KI reagent to a solution or directly on a potato or other materials such as bread, crackers, or flour. A blue-black color results if starch is present. If starch amylose is not present, then the color will stay orange or yellow.

Updated: 2nd October 2019

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