Making up starch solution

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Starch is a high molecular mass carbohydrate - (C6H10O5)n. Because of this starch is usually made up as a percentage solution rather as a molar strength.

Depending upon its final use and time available, there are variations on how to make up starch solution. Normally it should be nade up fresh, shortly before you need to use it. Distilled or deionised water should be used in all instances described here.

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.

There is no hazard normally associated with cold Starch solution other than it may stiffen your lab coat!
Method 1
This could be used when making up % solution for enzyme practicals.

  • Meausre out 10g of starch powder into a clean 2503beaker.
  • Pour in 20-30cm3 of distilled water and mix into a slurry.
  • In a second 1 Litre beaker boil about 500cm3 of water.
  • Add the starch mixture into the boiling water and continue boiling for a few minutes. An electric stirrer or hotplate stirrer could be used here!
  • Make up to the final volume accurately with very cold water
  • Allow to cool

When the starch is completely dissolved in the water, the cloudiness of the solution will dissapear.
Method 2
This is a quick method of making starch solution when final stregnth is not an issue, for example simple test for starch using Iodine solution.

  • Measure out 10g of strach powder into a clean 1 Litre beaker.
  • Boil water in an electric kettle
  • Add hot water to starch powder with continuos stirring for a minute.
  • Allow to cool
Starch solutions will hydrolyse over a period of time and particularly in an acid environment. Therefore if you need to 
store starch solution for a while then it can be preserved with Salicylic Acid.

See also

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