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SPUD STARCH TEST

Use iodine to test for the presence of starch in foods

Suitable For

Grade 7

Difficulty

2

Time Required

 <12 Hours

Supervision

Required

What’s it about?

Starch is made up of long chains of glucose molecules. When starch is combined with hot water it breaks up into a kind of starch/sugar molecule called ‘dextrin’. When the ‘dextrin’ is heated further, it breaks up into even finer sugar molecules called ‘maltose’. In this science experiment you will use ‘iodine’ to test for the presence of starch in a potato:

Topics covered

Starch, Indicator, Iodine

What will I need?

  • COOKING POT
  • BOWL OF WATER
  • LARGE RAW POTATO
  • PIECE OF CLOTH
  • 2x COFFEE FILTERS & FUNNEL
  • 2x DRINKING GLASSES
  • IODINE SOLUTION

Procedure (Method)

Unfortunately, this section is only available in the e-book version of the project.

How does it work?

Unfortunately, this section is only available in the e-book version of the project.

In this science experiment we use a chemical reaction that changes the colour of an ‘indicator’ (iodine) when there is a certain concentration of ‘starch’ in a given volume of water. When iodine comes in contact with starch, a deep purple-blue coloured substance is formed, and is a positive test for starch. A starch molecule is much larger than a sugar molecule and when starch is heated, it breaks apart into the smaller sugar molecules and allows it to be more easily digested.

The liquid in ‘glass 1’ still contains raw starch pressed out of the potato, and therefore the iodine makes the solution turn deep blue. The liquid in ‘glass 2’ contains no more starch, as heating it up further caused the starch to be broken up into a fine sugar, hence the colour is turned deep red/orange indicating that no starch is present anymore.

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