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Can Seliwanoff's test be used to distinguish sucrose from fructose?
Wiki User
∙ 13y ago
Yes, fructose is a ketose, for which Seliwanoff's test is most sensitive. Sucrose is neither entirely a ketose nor an aldose, but is a mixture of both. It will react, but more slowly, producing a much lighter pinkish color.
Wiki User
∙ 13y ago
Wiki User
∙ 13y agoYes. Sucrose is a disaccharide composed of glucose and fructose. Fructose is a ketose and therefore gives a positive result. The presence of a strong acid (HCl) in the reagent causes hydrolysis (splitting apart) of sucrose which yields free fructose for the reaction to take place.
Wiki User
∙ 13y agoFructose will need a lesser time to produce a red precipitate as compared to sucrose which need to hydrolyze first before producing red precipitate
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Why sucrose does not give a positive Benedict's test but hydrolyzed sucrose does give a positive beneditcts test?
Sucrose is formed from glucose and fructose.Sucrose is formed from glucose and fructose. Glucose and fructose gives positive test for benedict becuz both of them are reducing sugars whereas sucrose is not a reducing sugar so it gives negative test for benedict. On prolonged heating,sucrose will form glucose and fructose (reducing sugars)which ultimately gives a positive result .
Why does sucrose solution give a negative test with tollen's test?
A positive Tollen's test is given by compounds that have a free aldehyde or ketone functional group. Sucrose is a disaccharide composed of the monosaccharides glucose and fructose. In sucrose, the components glucose and fructose are linked via an ether bond between C1 (carbon with aldehyde group) on the glucosyl subunit and C2 (carbon with ketone group) on the fructosyl unit. The bond is called a glycosidic linkage. In other words, in sucrose there is no free aldehyde or ketone functional group. Hence sucrose will not answer Tollen's test.
Why did the enzyme lactase react with lactose but not sucrose?
Because, lactase breaks beta(1-4) glycosidic bonds between a galactose and a glucose, while sucrose molecule is formed by a dimer of a glucose and a fructose linked by an alpha(1-2) glycosidic bond.
Inulin is a polysaccharide composed entirely of fructose units.Which test be used to identify the presence of fructose?
You will have to do a test to find out if fructose is in the product. You can do this with some test strips.
Substances which are ve to anthrone test?
The anthrone test, tests for carbohydrates. The positive indicator is glucose since glucose is one of the most common monosaccarides and is found in many polysaccarides. Anthrone tests positive for fructose, ribose, maltose, and sucrose.
Why sucrose does not give a positive Benedict's test but hydrolyzed sucrose does give a positive beneditcts test?
Sucrose is formed from glucose and fructose.Sucrose is formed from glucose and fructose. Glucose and fructose gives positive test for benedict becuz both of them are reducing sugars whereas sucrose is not a reducing sugar so it gives negative test for benedict. On prolonged heating,sucrose will form glucose and fructose (reducing sugars)which ultimately gives a positive result .
How do you distinguish glucose and fructose?
Glucose is an aldose whereas fructose in a ketose. There is a simple qualitative test for distinguishing between D-Glucose and D-Fructose.
Which of the following pairs give positive toollens test-hexanal,acetophenone and fructose,sucrose?
The simple sugars will not react with the test because they are not aldehydes.
Why does sucrose solution give a negative test with tollen's test?
A positive Tollen's test is given by compounds that have a free aldehyde or ketone functional group. Sucrose is a disaccharide composed of the monosaccharides glucose and fructose. In sucrose, the components glucose and fructose are linked via an ether bond between C1 (carbon with aldehyde group) on the glucosyl subunit and C2 (carbon with ketone group) on the fructosyl unit. The bond is called a glycosidic linkage. In other words, in sucrose there is no free aldehyde or ketone functional group. Hence sucrose will not answer Tollen's test.
Why does sucrose not react to Benedicts when glucose and fructose its components do?
Fructose and glucose are joined by their glycosidic bond in such a way as to prevent the glucose isomerizing to aldehyde, or the fructose to alpha-hydroxy-ketone form. This stops it reacting to Benidict's reagent. However sucrose indirectly produces a positive result with Benedict's reagent if heated with dilute hydrochloric acid prior to the test, although after this treatment it is no longer sucrose. ;-)
What test can be used to identify the presence of the fructose?
Seliwanoff's test is used to differentiate aldose [glucose] from ketose [fructose]. Seliwanoff's reagent is composed of resorcinol and HCl. When heated with concentrated hydrochloric acid, the polysaccharides and oligosaccharides hydrolyze to yield monosaccharides. Then, resorcinol reacts in the dehydrated ketose to form oxymethylfurfurol produce a deep cherry red color [red precipitate]. Aldoses produces a faint pink colored solution.
Why the majority said that sucrose is a ketose sugar?
The majority would be incorrect. Sucrose is not considered an aldose or a ketose, because it is a disaccharide made from glucose (an aldose) and fructose (a ketose). So, it has both properties within its structure. It is a non-reducing sugar.It is possible that many say sucrose is a ketose because sucrose will fail the Benedict's test, which is designed to detect aldoses.
Why did the enzyme lactase react with lactose but not sucrose?
Because, lactase breaks beta(1-4) glycosidic bonds between a galactose and a glucose, while sucrose molecule is formed by a dimer of a glucose and a fructose linked by an alpha(1-2) glycosidic bond.
Inulin is a polysaccharide composed entirely of fructose units.Which test be used to identify the presence of fructose?
You will have to do a test to find out if fructose is in the product. You can do this with some test strips.
Substances which are ve to anthrone test?
The anthrone test, tests for carbohydrates. The positive indicator is glucose since glucose is one of the most common monosaccarides and is found in many polysaccarides. Anthrone tests positive for fructose, ribose, maltose, and sucrose.
Result for Lasker and Enkelwitz test?
fructose-blue to brick-red precipitate glucose-unchanged (blue to blue) lactose-unchanged galactose-unchanged ribose- blue to brick-red precipitate sucrose-unchanged starch-unchanged this test is to identify the ketoses. thus, from the results, only fructose and ribose are ketoses. fructose is ketohexose as it changed color in 20 minutes whereas ribose is ketopentose as it changed color in 10 minutes only.
Why does fructose give a positive Benedicts test?
Benedict's test detects the presense of the aldehyde group. Fructose is a ketose rather than an aldose, but it's converted to glucose or mannose (both of which are aldoses) by the base in Benedict's reagent. All monosaccharides give a positive Benedict's test because they're all either aldoses or alpha-hydroxy ketoses that get transformed into aldoses. Sucrose does not, because while it contains fructose and glucose, both of which do test postive, the saccharides in sucrose are "locked" into hemiacetal form and cannot undergo ring opening to expose an aldehyde group. (It's a very weak lock; dilute acid ... like, say, lemon juice ... will hydrolyse the saccharide linkage and allow the hemiacetal rings to open.)
