why does a solution made of starch get thick when heated in water?
Is starch insoluable? If it is, would the answer be because the solution just forms complexes of suspended solids which thinken the mixture?
Or would it be because granules of starch uncoil to give long strands that tangle into a gel?
(It kind of seems it could be both?)
http://en.wikipedia.org/wiki/Starch_gelatinization
I would go with the latter first. And note the correct spelling of insoluble (there is no able in it).
Both explanations you mentioned are correct and contribute to the thickening of a starch solution when heated in water.
Starch is insoluble in cold water, which means it does not dissolve completely. Instead, it forms complexes of suspended solids, as you mentioned. These complexes consist of granules of starch that disperse in water, forming a milky white mixture. However, when heat is applied to this starch-water mixture, the granules of starch undergo a process called gelatinization.
During gelatinization, the starch granules absorb water and start to swell. As they swell, the granules undergo physical and chemical changes. The granules progressively lose their structure and start to burst open. This bursting releases starch molecules into the surrounding water, forming long strands or chains.
These long starch chains, known as amylose and amylopectin, are responsible for the thickening of the solution. As the starch molecules disperse in the water, they start to intertwine and tangle with each other, creating a three-dimensional network of interconnected strands. This network traps water, causing the solution to become thicker and form a gel-like consistency.
So, to recap, when a starch solution is heated in water, the starch granules absorb water, burst open, and release starch molecules that then form a network of intertwined chains, resulting in a thickened, gel-like mixture.