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Title: Investigate the use of chemical reagents to identify starch, reducingsugars, proteins.
Hypothesis:
Objectives:
1. To make a number of other lower concentrations using a technique of
serial dilution.
2. To add a constant amount of Iodine indicator to each and using a
colorimeter to find how much light its absorbed through each sample.
3. To use this data to draw a graph to show the relationship between the
concentration of the starch and the light level.
4. To find out the concentration of starch in the samples of food.
Background Information:
Starch is an example of a natural polymer. A polymer is a long and repeating
chain of the same molecule stuck together. Starch is a long-chain polymer of
glucose molecules joined together. Starch, a whitewash, granular, organic
chemical that is produced by all green plants. Starch is a soft, white, tasteless
powder that is insoluble in cold water, alcohol, or other solvents. The basic
chemical formula of the starch molecule is (C6H10O5)n. Starch is a
polysaccharide comprising glucose monomers joined in α 1,4 linkages. The
simplest form of starch is the linear polymer amylose; amylopectin is the
branched form.
Iodine is a chemical element. The body needs iodine but cannot make it. The
iodine needed by the body must come from the diet. As a rule, there is very
little iodine in food, unless it has been added during processing. Processed
food typically contains more iodine due to the addition of iodised salt. Most of
the world's iodine is found in the ocean, where it is concentrated by sea life,
especially seaweed.
Iodine is the test for starch, when starch is present the yellow/orange iodine
solution becomes a blue/black colour. The iodine will be present in the centre
of the starch helix, forming a starch iodine complex. Starch is a carbohydrate
found in plants. It consists of two different types of polysaccharides that are
made up of glucose units which are connected in two different ways. One is
the linear amylose and the other is the branched amylopectin.
, Amylose is the compound that is responsible for the blue colour. Its chain
forms a helix shape, and iodine can be bound inside this helix.
Amylose forms a colloidal dispersion in hot water whereas amylopectin is
completely insoluble. The structure of amylose consists of long polymer chains
of glucose units connected by an alpha acetal linkage. Starch - Amylose shows
a very small portion of an amylose chain.
Boiling a starch solution causes temporary unwinding of the helix and the
subsequent release of the iodine molecule, the blue/black colour will
disappear, and when the helix cools down the blue/black colour will re-form.
This effect is measured by the quantity of concentration rather than its quality.
Colorimeter This instrument calculates the density of the coloured solution, for
example, when iodine is applied to starch, it can be used to determine the
concentration of a compound solution.
Reference:
https://en.m.wikipedia.org/wiki/Iodine_test
www.chemieunterricht.de 2006.
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