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Benedict’s test for reducing sugar

February 25, 2015 by Dr Hamza Arshad 24 Comments

This test is for finding whether the sugar is reducible or non reducible.It is both qualitative as well as quantitative test.This test is used for laboratory detection of different sugars as well as diabetes via urine test.

Principle of Benedict’s test:

When reducing sugars are heated in basic solution, they form powerful reducing compounds known as enedioles.Endiole further react with cupric ions which are present in Benedict’s solution to cuprous ions.Thus we detect the presence of reducing compounds.Here is should be noted that benedict’s solution not only react with reducing sugars but also give positive result with other reducing compounds.

Reagents for Benedict’s test:

Benedict’s solution contains:

  • CuSO4
  • Sodium citrate
  • Sodium carbonate (Na2CO3)

How to Check quality of Benedict’s solution?

Before performing test it is necessary to test the purity of Benedict’s solution.

Benedict’s solution is blue in color .In order to check purity of Benedict’s solution take 5 ml of Benedict’s solution in test tube and heat it.If is does not change color, it means it is pure.

Procedure of Benedict’s test:

  1. Take 5 ml of Benedict’s solution in a test tube.
  2. Add 5-8 drops of original solution in the test tube containing Benedict’s solution and heat it.
  3. Upon boiling, it will change the color.If it doesn’t change color, it means the sugar in the original solution is non reducible.

Precautions:

Here are some of the precautions for Benedict’s Test:

  • Measure the Benedict’s solution solution first.
  • Don’t add much solution. Add only few drops.
  • Heat the mixture gently.
  • Don’t keep the test tube towards any human while heating. Upon boiling it could escape test tube and burn skin.
  • Biol it few times before making any decision.

Benedict's test for reducing sugars

How to determine quantity of reducible sugar by Benedict’s test:

When can also determine the quantity of sugar in solution from Benedict’s test.

  • If the co lour upon boiling is changed into green, then there would be 0.1 to 0.5 percent sugar in solution.
  • If it changes color to yellow, then 0.5 to 1 percent sugar is present.
  • If it changes to orange, then it means that 1 to 1.5 percent sugar is present.
  • If color changes to red,then 1.5 to 2.0 percent sugar is present.
  • And if color changes to brick red,it means that more than 2 percent sugar is present in solution.

This way we can find whether the sugar in solution is reducing sugar or not.And we can also determine the quantity as well up to some extent.

Results:

If the solution changes its color to green, yellow, orange, red or brick red upon boiling, then it means that results are positive and the solution contains reducing sugar.

If there is no color change upon boiling, then it means that NO reducing sugar is present in solution and result is negative.

Sucrose doesn’t show positive results with Benedict’s reagent but if we reduce sucrose with the help of acid then its products would should positive results with Benedict’s solution. This way, we can confirm the reduction of sucrose as well.

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Filed Under: Biochemistry Tagged With: benedict's reagent, Benedict's test, principle of benedict's test

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. Bibi Ruqya says

    February 25, 2016 at 9:55 pm

    Thank you so much Hamza for this information

    Reply
  2. scott williams says

    March 30, 2016 at 5:21 pm

    Why do we care about testing the reducing sugar content ?

    Reply
    • scott williams says

      March 30, 2016 at 5:27 pm

      Whay is the purpose of the test?

      Reply
      • Admin says

        March 31, 2016 at 4:20 pm

        You will differentiate between reducing and non reducing sugars. After that you can perform other tests to find the exact sugar.

        Reply
  3. Maha khan says

    May 11, 2016 at 12:30 pm

    Why is Na2CO3 added to the solution before the Benedict’s test is performed?

    Reply
    • Admin says

      May 18, 2016 at 6:42 am

      it provides basic medium…

      Reply
      • Okoh says

        November 17, 2016 at 1:10 am

        so that…..

        Reply
  4. Hilary Nnanna says

    July 5, 2016 at 9:45 pm

    What is the work of the Sodium citrate in the reagent

    Reply
    • Admin says

      July 8, 2016 at 5:13 pm

      stabilizes the solution…

      Reply
  5. Hilary Nnanna says

    July 5, 2016 at 9:54 pm

    Why the spontaneous cooling in this Experiment

    Reply
  6. Hilary Nnanna says

    July 5, 2016 at 10:15 pm

    Why do reducing sugars in alkaline solution have strong reducing action on heavy metal ion

    Reply
  7. manpreet says

    August 20, 2016 at 12:01 pm

    why in benedict test, heating for more than 2 minutes is not carried out?

    Reply
    • Admin says

      August 21, 2016 at 6:59 pm

      i haven’t written anywhere in my post that you should not heat for more then 2 minutes. But 2 minutes are enough for reaction.

      Reply
  8. lazyboi says

    September 24, 2016 at 5:54 pm

    why is sodium bicarbonate added before the benedicts solution in finding a reducing sugar

    Reply
    • Admin says

      October 3, 2016 at 7:17 am

      probably for pH…but i will get back with more precise answer.

      Reply
  9. Sakshi Patel says

    November 21, 2016 at 5:04 pm

    why we add only 5-8 drops of reagent not more than it?

    Reply
    • Admin says

      December 3, 2016 at 8:15 am

      because it is enough for the reaction.

      Reply
  10. Rodric says

    January 24, 2017 at 6:45 pm

    Thanks Admin

    Reply
  11. Asmat says

    June 6, 2017 at 3:48 pm

    We have to add reagent to the sample or saurine sample to reagent ? Plz xplain

    Reply
    • Admin says

      June 9, 2017 at 1:04 am

      add sample to reagent…

      Reply
  12. Brilliant says

    July 2, 2017 at 9:25 am

    why the spontaneous cooling?

    Reply
  13. Ayogu Kosisochukwu says

    August 13, 2017 at 12:15 pm

    Why the spontaneous cooling in Benedict’s test

    Reply
  14. Andrew Hilarczyk says

    October 17, 2017 at 5:50 pm

    Could a positive Benedicts test occur without boiling if left for an extended period of time (72+hrs) at room temperature?

    Thanks!

    Reply
  15. oli says

    October 30, 2018 at 4:06 pm

    hi good ting

    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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