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Why do disaccharides and polysaccharides give positive Molisch Test?
Wiki User
∙ 13y ago
simply because they are carbohydrates, all carbohydrates produces positive result in molisch's test
All carbohydrates i.e. monosacchardes, dissacharides and polysaccharides are dehydrated (lose water) by a dehydrating agent (e.g. Sulphuric acid) they form aldehydes known as furfurral. The furfurral reacts with a component known as 1- naphthol present in Molisch reagent resulting in a reddish violet colour forming between the Reagent and the previous mixture of the carbohydrate and thedehydrating agent. It is important to note that the reaction is more rapid with simple sugars or monosaccharides
Wiki User
∙ 13y ago
Wiki User
∙ 10y agoI think it is beter to discuss the principle of this test first.
Any monosaccharide can answer this test (gives positive result).
This happens through dehydration by sulfuric acid (H2so4); this dehydration results in production of furfural or one of its derivatives depending on the type of monosaccharide whether it's hexose ( gives 5-hydroxymethylfurfural) or pentose (gives furfural). Then this furfural reactes with 2 molecules of phenol (usually α-naphthol, though other phenols (e.g. resorcinol, thymol). The product of this reaction has red or purple colored (the positive ).
Now regarding your question if the positive means the presence of carbs (sugars). The answer is that it can be a sugar or [furfural (not a sugar or carbs)]. Actually I am not sure if there is another compund also gives positive result.
N.B. Disaccharide and polysaccharides must be hydrolyzed using HCl to produce monosaccharides before giving the result. If you get any negative result with Molisch, you can proceed to hydrolysis step then redo the test. if it still negative the substance you test is not a sugar. On the other hand, if it turns to positIve, that means it was either disaccharide or polysaccharide.
To conclude this, I can tell you that the negative result exclude the presence of the carbohydrates but positive can't give any evidence that the substance give the result is carbohydrate. In other words, a negative result by this reaction is a very good evidence of the absence of carbohydrates, but a positive test is indication to the probable presence of carbohydrate.
I think further tests must be done.
Wiki User
∙ 15y agoyes, with very few exceptions a positive Molisch's test confirms the presence of carbohydrates.
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Would you be able to distiguish maltose from lactose in a unknown sample from doing barfoed's test?
Both maltose aswell as lactose are disaccharides, where maltose is made up of two glucose units, whereas lactose is made up of 1 unit of glucose and 1 unit of galactose. Barfoed's test answers only for mono and disaccharides. Presence of red precipitate would indicate a positive result for monosaccharides. Thus doing Barfoed's test does not distinguish between maltose and galactose since both are disaccharides.
Is it possible to be positive on a ovulation test and a week later get a positive pregnancy test?
After your ovulation takes place, you'll need to wait at least 10 days to take a pregnancy test and, hopefully, get positive results. Good luck!
Are substances that test positive with the Ames test necessarily carciongenic in humans?
The substances that are test positive with Ames test may or may not be carcinogenic for humans. Similarly, some substances that cause cancer in laboratory animals do not give a positive result Ames test. It is not possible to decide the carcinogenicity of any substances only depending on the Ames test.
What observation indicates a positive test for lipid?
If it is mixed well.
What conclusions can you draw when an experimental sample gives both a positive starch test and a positive maltose test after incubation?
Starch digestion (hydrolysis) is incomplete
Will disaccharides and poly saccharides give a positive result to molisc test?
Yes, both disaccharides and polysaccharides will give a positive result in a Molisch test. The Molisch test detects the presence of any compound containing a significant amount of glycosidic bonds, which are present in both disaccharides and polysaccharides.
Will disaccharides and polysaccharides give positive result for molisch test?
Yes, both disaccharides and polysaccharides will give a positive result for the Molisch test. The Molisch test detects the presence of any compound that can be dehydrated to furfural in the presence of concentrated sulfuric acid, which includes carbohydrates like disaccharides and polysaccharides.
Why is the molisch test slower with disaccharides?
The Molisch test detects carbohydrates by breaking them down to monosaccharides. Disaccharides need to be hydrolyzed into their constituent monosaccharides before they can react with the Molisch reagent, which makes the test slower compared to monosaccharides that can react directly.
Why albumin gives positive Molisch test?
Because it is a carbohydrates and molisch test will be positive in the presence of carbohydrates
Does Benedict test indicate monosaccharides polysaccharides and disaccharides?
The Benedict test is useful for monosaccharides and disaccharides.
What is the positive result for molisch test?
all carbohydrates show positive result to Molisch test. this is because Molisch test is used to distinguish carbohydrates from other organic compound.
What does a positive Molisch's test on an unknown substance indicate?
A positive Molisch's test result indicates the presence of carbohydrates.
Why does glycoproteins reacts positively with Molisch reagent?
Glycoproteins give positive results for Molisch's test. This answer is true because Molisch test was a test for sugar.
Why polysaccharides are tasteless and disaccharides are sweet?
Why poly saccaride are test
What is the chemical basis for a positive test in Molisch's test?
See this link.
What group of substance that give positive reaction to molisch test?
Carbohydrates typically give a positive reaction to the Molisch test. This is because the Molisch reagent reacts with the carbohydrates to form a purple complex, indicating the presence of sugar molecules in the solution.
Why egg albumin gives the negative result for molisch test?
Egg albumin gives a negative result for the Molisch test because it does not contain carbohydrates. The Molisch test is used to detect the presence of carbohydrates, and since egg albumin consists mainly of proteins with little to no carbohydrates, it does not react with the reagents used in the Molisch test to give a positive result.
