why starch gives blue colour with iodine

cellulose is derived from D-glucose units, which condensed through beta(1- 4)-glycosidic bond. This give cellulose to be a straight polymer therefore, it can't coil around iodine to produce blue color as starch does. To approximately 2 cm of starch solution two drops of iodine/potassium iodide solution were added. A blue-black colour indicates the presence of starch as a starch-polyiodide complex is formed. Starch is only slightly soluble in water, but the test works well in a suspension or as a solid.
In this ar]ti]cle, we will use a 5% al]co]hol so]lu]tion of which is used in medicine, and the ma]jor]i]ty of re]ac]tions car]ried out inPlab]o]ra]to]ries. Starch in]ter]acts with io]dine, form]ing in]clu]sion com]pounds, i. e. clathrates.


This chem]i]cal process was dis]cov]ered back in 1814 by the sci]en]tists Jean Jacques Col]in and Hen]ri-Franois Gaulti]er dePClaubry In]clu]sion com]pounds are spe]cial com]pounds in which the mol]e]cules of one sub]stance en]ter the molec]u]lar struc]ture of an]oth]erPsub]stance. In this case, amy]lose mol]e]cules (one of the main polysac]cha]rides of starch) will be the hosts and the mol]e]cules will be the guests. Click to see more stun]ning ex]per]i]ments with io]dine. This is quite a sim]ple chem]i]cal ex]per]i]ment which can be car]ried out at home and shown to chil]dren, to in]spire them with a love forPchem]istry. stir]ringProd. Pour wa]ter into the test tube and add 4-5 drops of io]dine.


Add a pinch of starch and mix well with a rod. The re]sult will be a dark bluePso]lu]tion. In]ci]den]tal]ly, you can also re]peat this ex]per]i]ment in oth]er ways, for ex]am]ple add one drop of io]dine to a small mound of starch, and a dark blue patch will ap]pear. You can also drip io]dine on to half a pota]to, as it has a high starch con]tent: if you im]merse a peeled pota]to in cold wa]ter, starch par]ti]cles will ap]pear in the wa]ter af]ter a cer]tain pe]ri]od of time. If you hold a peeled pota]to in your hands, they will also be]come coat]ed withPstarch. If you heat a test tube con]tain]ing a so]lu]tion of starch, io]dine and wa]ter over a spe]cial chem]i]cal burn]er for 10 sec]onds, the so]lu]tion will turn a white, trans]par]ent col]or.


This is be]cause the com]pound of io]dine and starch is un]sta]ble, but if you put the test tube in cold wa]ter, a dark blue sed]i]ment will form oncePmore. When starch is heat]ed to boil]ing point, it be]gins to break down, and the chains of amy]los]es break, thus form]ing short chains of dex]trins, so the col]or starts to change. Sep]a]rate com]pounds of glu]cose do not give any col]or in a re]ac]tion withPio]dine. An in]ter]est]ing fact: Amy]lopectin, a polysac]cha]ride of starch, gives a pur]ple-red col]or]ing when re]act]ed with io]dine. There is sig]nif]i]cant]ly more amy]lopectin in starch than amy]lose, which gives a blue col]or, but the blue col]or over]rides the red-pur]plePcol]or.

  • Views: 126

why do we have to eat healthy food
why do plants have these other pigments besides chlorophyll
why do we need sugar in our body
why put salt in boiling water for pasta
why do you need baking soda in cookies