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Molisch’s test-Qualitative test for the presence of carbohydrates

August 6, 2016 by Dr Hamza Arshad 73 Comments

Molisch test is a qualitative test for determining the presence of carbohydrates in a solution.It is named after an Austian botanist “Hans Molisch” who discovered this test for the presence of carbohydrates.

It is a general test for the presence of carbohydrates and is positive for all kinds of carbohydrates which in free from or in combined form.

 

molisch's test principle, reagents, procedure, results

<photo credit>

Principle of molish’s test:-

For detecting the presence of carbohydrates, the solution is first treated with a strong acid.This is for hydrolysing the carbohydrate to monosacharide.When water is removed from monosaccharides, a compound called furfurol is formed.This furfurol is condensed to form a violet ring or other colored compound.The compound furfurol is condensed with alpha nephthol or other phenol present in molisch’s reagent.

Importance of molisch’s test:-

Molisch test is very important because it is a general test for the presence of carbohydrates.It is used widely as compared to other tests because before every specific test for different carbohydrates a general test is important and that general test is performed via molisch test.Another important thing is that, this test is positive for all types of carbohydrates whether free or in combined form like glycoprotiens,glycolipids etc.

Procedure of Molisch’s test:-

If you want to find the presence of carbohydrates in a given solution then just follow the below procedure of molisch test and you will find whether the given solution contains carbohydrates or not.

  1. Take 5ml of solution in a test tube with the help of pipette.
  2. Add two to three drops of molisch reagent.
  3. Mix it gently for some time.
  4. Incline the test tube and slowly add a few drops of strong mineral acid.(Sulphuric acid or hydrochloric acid).
    Observation
  5. You will observe reddish violet ring formed at the junction of the acid and carbohydrate solution.

Precautions of Molisch test:

Here are some of the things you would need to take care of while performing this test:

  • First of all the most important thing you need to know is to add acid at the side of test tube. Don’t add it directly.
  • Then you would need to add acid drop by drop. Do not add all the acid once.
  • Measure the solution before adding it.
  • Add only few drops of molisch’s reagent. You don’t need to add much.
  • Add acid with great care as we use strong acid in this test and it could burn your skin.
  • Don’t shake the test tube when ring is formed. If you do so, you would destroy the ring.

If you perform all the steps as mentioned above correctly, you would definitely get a positive result, i.e violet ring if carbohydrates are present in your solution.

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Filed Under: Biochemistry Tagged With: molisch's test, principle of molisch test, procedure, reagents

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. muntaha says

    November 1, 2015 at 6:24 pm

    plz i have a question why purple ring is formed between two layers ……..and why we add acid slightly and through the side of tube??

    Reply
    • Admin says

      November 1, 2015 at 8:42 pm

      When furfural is condensed it is in the form of colored compound and here in this experiment the colored compound is in the form of ring. And we add acid through the side of the tube so that both the solutions don’t mix and the ring is not disturbed. If you add the acid directly it will destroy the ring.If both the layers mix, the layer of reaction would be dispersed and the results would be not accurate.
      Hope this answer your question.

      Reply
      • muntaha says

        November 2, 2015 at 12:54 pm

        yes yes 100 percent thanks sir

        Reply
        • muntaha says

          November 2, 2015 at 12:59 pm

          plz i have another question….and question is ….the ring is formed after adding acid due to dehydration or before??

          Reply
          • Admin says

            November 2, 2015 at 1:36 pm

            Yes ring is formed after adding acid. This hydrolyze CHO and furfural is formaed. it then reacts with alpha nepthol which is already present in test tube. The two layers don’t mix because we add the acid slightly and condensation takes place only in the surface molecules, thus violet ring appears on the surface.

        • Chinedu Sig says

          December 22, 2015 at 2:41 pm

          The ring is formed between the layers of denser sulphuric acid and test sample of lower SG. I think the reason for adding the acid slowly through the sides is to avoid splashing of the corrosive acid.

          Reply
          • Admin says

            December 23, 2015 at 12:26 pm

            you could be right but if you don’t add acid slowly through the side then they layers are mixed and ring is not formed which means that both the layers should not be mixed.

      • jessica says

        September 14, 2016 at 10:17 am

        hello
        i was just wondering does this mean, if the layer of reaction disperses as you stated in the top question that we would get a negative result rather than a positive one.
        Thanks

        Reply
        • Admin says

          September 14, 2016 at 6:06 pm

          no that would could be your fault. if ring is formed and then damaged then it should be positive result. but if ring is not formed and you think you have done mistake (not adding acid to sides), you should repeat it again.

          Reply
    • Reilly says

      February 12, 2017 at 9:27 pm

      Please how would you conclude this test

      Reply
  2. fasal says

    December 8, 2015 at 5:10 pm

    sir i have a doubt what is the compound present in that purple ring??????

    Reply
    • Admin says

      December 8, 2015 at 6:08 pm

      it is the condensed form of furfural. read the principle of molisch test above.

      Reply
  3. Nomski says

    December 9, 2015 at 5:08 pm

    Why does the ring disappear when the test tube is shaken and the whole solution changes color to purple?

    Reply
    • Admin says

      December 12, 2015 at 3:08 pm

      Because when the ring is formed at the junction, it means that the compound that is formed because of reaction is only there (at junction). But when you shake it, the compound is mixed in all the solution.

      Reply
  4. shaswat das says

    December 17, 2015 at 6:33 am

    what are the compounds other than carbohydrates that give this test? what are the carbohydrates that dont give this test?

    Reply
    • Admin says

      December 19, 2015 at 11:02 am

      it is general test for carbohydrates and all carbohydrates either in free from or in combination with other compounds like glycolipids, glycoproteins etc will give positive molisch’s test.

      Reply
  5. ossyfrank Chidume says

    January 2, 2016 at 8:23 am

    Question sir, when water is used as control, what color result?

    Reply
    • Admin says

      January 4, 2016 at 7:31 pm

      Sorry, don’t know about this.

      Reply
    • Arielle A. De Jesus says

      February 25, 2016 at 1:18 am

      Water will yield a negative result in Molisch’s test. Nothing will actually happen to the water.

      Reply
  6. PATRICK K says

    January 8, 2016 at 3:37 am

    Please sir, I have a question. My question is, Can Benedict’s test which is also a test for carbohydrates be used to test for diabetes? Give reasons.

    Reply
    • Admin says

      January 8, 2016 at 8:41 pm

      Yes, benedict’s test can be used to find glucose in urine which can indicate diabetes but that is not the best way to diagnose diabetes. The best way to diagnose diabetes is quantitative test for blood glucose level. and one of the accurate test for blood glucose estimation is glucose method or glucose oxidase test…Hope this helps…you can read more about Benedict’s test here: https://allmedicalstuff.com/benedicts-test/

      Reply
  7. Tetio blondio says

    January 16, 2016 at 5:12 pm

    What is the biochemistry behind the experiment that makes us conclude that the unknown compound is a carbohydrate

    Reply
    • Admin says

      January 18, 2016 at 2:13 pm

      because this voilet ring is only formed if CHO is present in solution.

      Reply
  8. elvis obi says

    January 16, 2016 at 10:06 pm

    sir, can you please tell me the general tests for carbohydrates, ‘cos i dont think Benedict’s test, iodine, fehling’s test, barfoed’s test and seliwanoff’s tests are general test for carbohydrates.

    Reply
    • Admin says

      January 18, 2016 at 2:06 pm

      Molisch’s test is the general test for carbohydrates…benedict’s, iodine etc are for specific CHOs…

      Reply
  9. Fatuk says

    January 22, 2016 at 9:40 pm

    Sir,
    Pls why do we boil in the bial’s test? I mean what is the significant of the boiling.

    Reply
    • Admin says

      January 31, 2016 at 10:29 am

      Sorry don’t have answer at the moment, but i would definitely write a separate post on bail’s test and would answer your question there. Keep visiting allmedicalstuff.com

      Reply
  10. imrana says

    January 23, 2016 at 3:51 pm

    what ar the precaution of this test sir

    Reply
    • Admin says

      January 31, 2016 at 10:26 am

      post update with heading of precautions in it. Read it…

      Reply
  11. Balraj says

    February 7, 2016 at 5:28 am

    Sir, what happens when we add excess of molisch reagent

    Reply
    • Admin says

      February 8, 2016 at 4:23 pm

      why waste your reagent if you can get results with only 2-3 drops…

      Reply
  12. yana says

    March 9, 2016 at 6:29 pm

    sir, why there are also crystal formation in sample between the ring?

    Reply
    • Admin says

      March 9, 2016 at 7:15 pm

      sorry…

      Reply
  13. Amos says

    March 16, 2016 at 12:44 am

    Sir please what of anthrone test of starch and sucrose what colour does it indicate after mixing thoroughly

    Reply
    • Admin says

      March 16, 2016 at 2:12 pm

      don’t know about anthrone test at the moment, but will write a new post about it in coming days…stay tuned to all medical stuff…

      Reply
  14. Amos says

    March 16, 2016 at 12:45 am

    And molisch test of sucrose and search

    Reply
    • Admin says

      March 16, 2016 at 2:10 pm

      its would be positive for all carbohydrates including sucrose and starch…

      Reply
  15. OMA says

    March 21, 2016 at 3:17 pm

    Sir please, what is the role of sulphuric acid and what does the ring signify?

    Reply
    • Admin says

      March 21, 2016 at 4:14 pm

      sulfuric acid hydrolyses carbohydrates to simple sugars. The ring show that Carbs are present and this ring is only formed when furfural is condensed.

      Reply
  16. OMA says

    March 29, 2016 at 11:24 am

    Tnk u admin…pplz is molisch test a specific test for carbohydrates,with reasons?

    Reply
  17. Fitri Aiman says

    May 7, 2016 at 2:39 pm

    i just wanna to ask… i have done this experiment by using glucose, xylone, fructose, maltose and sucrose.. but the product different for each of one.. glucose, xylone and fructose have slightly same colour.. but sucrose and maltose have different than the other 3.. can you explain to me why this happen??

    Reply
    • Admin says

      May 7, 2016 at 2:51 pm

      Theoretically all of the carbs should give positive results. Personally i have performed this test on only one sugar therefore, can’t say anything.

      Reply
  18. Ricardo Andrade Aranda says

    May 18, 2016 at 12:06 am

    I just performed this test and I’m looking for info. to make my report; insted of the ring in the junction of the solution, I obtained a purple precipitate, and that’s the result I was supposed to get., only my glucose solution formed a very thin purple ring on the surface (again, that result was expected by my professor), so my question is: in which conditions is the precipitate normal for the molisch test? in which conditions the positive result will be a ring?
    Thanks in advance and sorry for my bad English.

    Reply
    • Admin says

      May 18, 2016 at 6:31 am

      ring would form with all the carbs….when the solutions turns purple and ring doesn’t form it means that you have mixed the two solutions…if you do it correctly and the two solutions doesn’t mix, you would definitely obtain a ring.

      Reply
  19. Phil Soglo says

    September 19, 2016 at 9:50 pm

    Sir, you said the violet ring forms because of the aldehyde group present in the carbohydrate. Does it mean keto sugars don’t give a positive result since there’s no addition of an alkaline to convert the keto group to and aldehyde?

    Reply
    • Admin says

      October 3, 2016 at 7:17 am

      sorry will answer this later or will update the post for you.

      Reply
  20. acms says

    October 24, 2016 at 5:38 am

    i have done molich test for fructose but it is giving brown ring instead of puple..Can u please help me out about whats going wrong with fructose

    Reply
    • Admin says

      October 26, 2016 at 2:19 pm

      don’t have experience about this but fructose should also give purple ring.

      Reply
  21. Abdurrahman Akram says

    November 2, 2016 at 10:45 pm

    Sir, I have a few question to ask about this experiment
    Is it okay if we didn’t add sulphuric acid?
    What’s the name of the purple ring formed?
    Why the tube become hot when shaking/mixing?
    Why Molisch test considered as a general indicator for all types of sugar?
    Which type is the fastest to show the purple ring?
    Thank you!

    Reply
    • Admin says

      November 4, 2016 at 6:53 am

      1. no sulphuric acid is must.
      2. it is condensed form of furfural.
      3. due to reaction.
      4. because it gives positive result with solution containing any type of sugar.
      5. sorry, don’t know about any method which will speed up the reaction.

      Reply
  22. Wafa says

    December 11, 2016 at 3:08 pm

    Tell me about apparatus that used for molisch’s test?????

    Reply
    • Admin says

      December 13, 2016 at 7:40 pm

      mentioned in the post…but i will add a separate heading.

      Reply
  23. Chawan says

    January 11, 2017 at 7:21 pm

    Plz i have a question why monosaccharides gives a rapid positive test , disaccharides and polysaccharides react slower ?

    Reply
    • Admin says

      January 12, 2017 at 9:09 am

      because disacchariedes and polysaccharides have long chains which takes time to break and react.

      Reply
  24. Brilliant says

    July 2, 2017 at 8:35 am

    condensation reaction in molisch’s test removes which chain??

    Reply
  25. Dr.Staleymo says

    July 9, 2017 at 1:25 pm

    I have a question . ..what is the results and conclusion of starch using molisch reagent

    Reply
    • Admin says

      July 18, 2017 at 8:59 pm

      results are mentioned above at the end of procedure.

      Reply
  26. Aishat says

    July 31, 2017 at 5:48 pm

    can’t we know the specific type of carbohydrate is present?

    Reply
    • Admin says

      August 20, 2017 at 6:24 pm

      no…for that there are other tests that you can study from our site…i have written about tests for all the individual carbohydrates.

      Reply
  27. jhums says

    August 20, 2017 at 10:59 pm

    does fructose have thicker layer of violet in the interface formed than in glucose

    Reply
  28. Jale Francheska B. Bahian says

    August 21, 2017 at 4:54 pm

    I have a question sir, why is it that in our experiment, glucose, ribose, and starch don’t have a formation of purple product?

    Reply
  29. Himy says

    October 31, 2017 at 7:38 pm

    Why is a black ring formed sometimes at the junction of the two liquids instead of a purple one?

    Reply
  30. oluchi Tonia says

    February 8, 2018 at 9:20 pm

    pls what role do conc H2SO4 play in molisch reagent

    Reply
    • Admin says

      February 23, 2018 at 2:56 pm

      clearly mentioned in the principle.

      Reply
  31. zahoor uddin says

    March 9, 2018 at 4:39 am

    sir, why moliisch’s test is called qualitative test ? what is the reason behind this ?

    Reply
    • Admin says

      March 26, 2018 at 4:48 pm

      the reason is mentioned above in the post if you have read carefully…it is called qualitative test because it tells you whether the solution contains carbohydrate or not.

      Reply
  32. Huzefa says

    March 16, 2018 at 11:08 pm

    Sir I want to ask, why we must preserve the ring rather than observed that it has produce purple color?, isn’t it the same, because the purple color formed by the purple ring which is formed due to carbohydrate is presence in the solution, so if I shake the tube and the whole sample became purple, it’s still a positive result right?

    Reply
    • Admin says

      March 26, 2018 at 4:43 pm

      what i have learned is that the ring is diagnostic so you should focus on the ring.

      Reply
  33. Amira Zainal says

    April 15, 2018 at 6:28 am

    Sir, i did the test few days ago using several known sugar solution and one of the sugar solution was fructose. However, it gave out negative result. May i know the possible reason why this could happen? Thank you.

    Reply
    • Dr Hamza Arshad says

      April 20, 2018 at 8:23 pm

      fructose should give positive result…may be you did some mistake in the test.

      Reply
  34. Sunita says

    September 18, 2018 at 9:22 am

    sir, i have done the mollish test several times with glucose and fructose but the ring has been formed at the bottom not at the junction. please expain

    Reply
    • Dr Hamza Arshad says

      March 11, 2019 at 7:47 pm

      may be you mixed both the solutions vigorously…

      Reply
  35. Abdullah says

    April 25, 2019 at 7:04 pm

    explain appear the violet ring between two layers:acid layer in bottom of test tube and sugar solution layer in the surface?

    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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