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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

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13y ago
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10y ago

I 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.

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14y ago

yes, with very few exceptions a positive Molisch's test confirms the presence of carbohydrates.

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Q: Why do disaccharides and polysaccharides give positive Molisch Test?
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Will disaccharides and polysaccharides give positive result for molisch test?

Yes they will. Disaccharides will give a positive result much quicker than polysaccharides, and it also depends on the conditions because they need to be dehydrated by an agent such as concentrated H2SO4 and it so happens that it is much easier to do so on a disaccharide than it is on the polysaccharide

Does Benedict test indicate monosaccharides polysaccharides and disaccharides?

The Benedict test is useful for monosaccharides and disaccharides.

Why albumin gives positive Molisch test?

Because it is a carbohydrates and molisch test will be positive in the presence of carbohydrates

What does a positive Molisch's test on an unknown substance indicate?

A positive Molisch's test result indicates the presence of carbohydrates.

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.

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.

Is molisch's test is specific test for glucose?

what is the name of result from molisch test

Name the 2 tests of carbohydrates anaylsis that are based on the reduction of Copper ions.Select one:a. Benedict’s and barfoed’s testb. Barfoed’s test and molisch testc. Molisch test and iodined. Salivanof and osazonee. Benedict’s and iodine test?

Molisch Test and iodine.

Will disaccharides and poly saccharides give a positive result to molisc test?

all carbohydrates will give a positive visible result

Why egg albumin gives the negative result for molisch test?

Molisch's test is used to detect carbohydrates. Egg albumen is free from carbohydrates.