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Iodine test for starch

February 22, 2015 by Dr Hamza Arshad 8 Comments

Starch is the carbohydrate storage unit of plants.It can be detected in a solution via starch-iodine test.If you have an unknown solution and you are asked to detect whether starch is present in this solution or nor, you would have to perform starch test.For this test,follow the procedure below.

When iodine solution react with start a bluish color is obtained indicating the presence of starch.But this test can be affected by temperature and pH, which is explained below.

iodine test for starch

Iodine test for carbohydrates:

If you want to distinguish between monosaccharide, disaccharides and polysaccharide, you should perform iodine test.This test would be positive for polysaccharide and negative for mono and disaccharides.

When iodine dissolved in potassium iodide solution react with starch or glycogen, it react with it and the color of solution is changes, indicating the presence of these polysaccharides.

 

Principle of iodine test:

Some polysaccharides have have the property of adsorption for iodine.So, they adsorb iodine and give coloration.

Reagents for iodine test:

Iodine solution containing:

  • Potassium iodide and water

Procedure for performing iodine test:

  1. Take 1 ml of original solution and add it to a test tube.
  2. Add 1 to 2 drops of drops of iodine solution in it at room temperature.
  3. If the color of the solution changes, it means that polysaccharides are present in the original solution.
  4. Starch gives blue color while glycogen gives red color.While monosacchardes and disacchardes do not change color when treated with iodine solution.

Effects:

Effect of pH on iodine test:

At low pH, like when acid (HCl or any other) is added to the solution, the color will turn dark blue.While in case of base such as NaOH complex will break and colour will disappear.

Effect of temperature on iodine test:

At low temperate solution gives blue color when treated with iodine solution.While in case of high temperature, complex breaks and color disappears.

Precautions:

  • You should not add acid or base in the solution because it will not give correct results with high or low pH.
  • The test should be done at room temperature because change in temperature can alter results.
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Filed Under: Biochemistry Tagged With: iodine test, iodine test for carbohydrates, iodine test for starch

About Dr Hamza Arshad

Hamza is the writer and owner of this blog. He is a hobby blogger and student of MBBS in BMC (Bannu Medical college). He blogs to help others and share his knowledge with others.

Comments

  1. wisal khan says

    May 30, 2015 at 8:21 pm

    tnks hamza.u made my practical easier

    Reply
  2. FRED ORIKO.....Kenya says

    October 28, 2015 at 5:56 pm

    thanks a lot Hamza
    you off load my practical burden

    Reply
  3. Dumisa says

    March 14, 2016 at 8:52 pm

    Much appreciated Hamza. Am so positive about my practical write up anddi understand mostly why I was doing it.

    Reply
  4. samujoky best says

    April 24, 2016 at 12:00 pm

    Hmm how sweet I just got what I was looking for thanks

    Reply
  5. vivian says

    May 28, 2016 at 9:47 am

    thankyou alot

    Reply
  6. damera says

    June 5, 2017 at 7:46 pm

    Awesome!!!!! Found it useful

    Reply
  7. Medhavi Fernando says

    December 2, 2017 at 3:27 am

    Can you please explain the mechanism of changes in starch due to the changes in the?

    Reply
  8. Kelly says

    March 2, 2018 at 7:55 pm

    Pls why are they different colours when test on starch with iodine

    Reply

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Hamza is the writer and owner of this blog. He is a hobby blogger and student of MBBS in BMC (Bannu Medical college). He blogs to help others and share his knowledge with others.

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