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Starch is a polysaccharide made up of many glucose units joined together in long chains. Benedict's reagent detects reducing sugars, which have a free aldehyde or ketone group that can react with the reagent to produce a colored precipitate. Starch does not contain these reactive groups, so it does not give a positive reaction with Benedict's reagent.
Because it is a so-called nonreducing sugar in neutral or alkaline solution.
In acidic solution however (e.g. in sugar containing limonades),
the nonreducing di-saccharide sucrose is quit easily turned ('hydrolysed' or split) into
the two mono- saccharides glucose and fructose, which are in fact (in this test) reducing.
- The aldose glucose is a straight forward reducing sugar, so positively detected by B's test reagent.
- The ketose fructose is not strictly a reducingsugar (it is an beta-hydroxy-ketone, not an aldehyde), but it becomes reducing thus giving a positive test.
This is because this 'alpha-hydroxy-ketone' is converted to the aldoses: glucose and mannose, by the alkaline solution of the Benedict's test (called 'keto-enol'-tautomerisation).
sucrose is a glucose polymer that doesn't have the free carbonly group to react with the benedicts solution.
Benedict's Reagent tests only for 'reducing sugars' (monosaccharides), starch is a polysaccharide
Benedict's solution reacts with simple sugars like glucose, which are monosaccharides. Sucrose is not a simple sugar, it is a disaccharide.
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If benedicts reagent turns red what substance is present?
If Benedict's reagent turns red after adding it to a solution, it indicates the presence of reducing sugars such as glucose or fructose. The red color is a result of the reduction of copper (II) ions in the reagent to copper (I) oxide by the reducing sugars.
Explain the chemical mechanism for detecting indole in a bacterial culture?
Indole can be detected in a bacterial culture by using Kovac's reagent, which reacts with indole to produce a red color. The chemical mechanism involves the reaction between the indole and the reagent, resulting in the formation of a red complex that can be visually observed. This test is commonly used in microbiology to differentiate between bacteria that can produce indole (positive result) and those that cannot (negative result).
An unknown sample is tested with both biuret reagent and benedicts reagent both test result in a blue color what has been learned and why are these called negative results?
The blue color observed with both the biuret and Benedict's reagents indicates that proteins are not present in the sample. These results are considered negative because they do not indicate the presence of proteins or reducing sugars, which the biuret and Benedict's tests are specifically designed to detect, respectively.
How IMViC tests differentiate Escherichia coli from Enterobacter aerogenes?
IMViC tests differentiate Escherichia coli from Enterobacter aerogenes by examining their biochemical properties. E. coli typically produces a positive result in the Indole and Methyl Red tests, while Enterobacter aerogenes tends to produce a positive result in the Voges-Proskauer and Citrate tests. This differentiation is based on the different metabolic pathways and enzyme activities of the two bacteria.
What is Oxidase test results for bacillus subtilis?
Bacillus subtilis is positive for the oxidase test. This means that it has the enzyme cytochrome c oxidase, which is needed for the bacterium to produce energy through aerobic respiration. The positive result is indicated by the appearance of a color change (usually dark purple) on the test strip after adding the reagent.
Does using benedicts reagent on honey produce a positive result?
Yes, Benedict's reagent can produce a positive result when used on honey containing reducing sugars, such as glucose or fructose. The reagent will change color from blue to green, yellow, orange, or red depending on the concentration of reducing sugars present in the honey.
Indication of a negative result with Bial's Reagent?
A negative result with Bial's reagent will show no color change, indicating the absence of pentoses in the test sample. This can be confirmed by the lack of a green color formation, which is characteristic of a positive result when pentoses are present.
If benedicts reagent turns red what substance is present?
If Benedict's reagent turns red after adding it to a solution, it indicates the presence of reducing sugars such as glucose or fructose. The red color is a result of the reduction of copper (II) ions in the reagent to copper (I) oxide by the reducing sugars.
What substrate gives a positive reaction for benedicts reagent?
Reduction of Benedict's reagent occurs with reducing sugars such as glucose, fructose, and galactose, giving a positive test result. This test is used to detect the presence of reducing sugars in various food products.
When glycogen is added to benedicts reagent why would it remains blue?
Although glycogen is a carbohydrate, it is classified under POLYSACCHARIDES which are non-reducing sugars. Benedict's reagent is used to test for the presence of non-reducing sugars. The positive result for this is a brick-red precipitate or solution. It remained blue (which is negative) due to fact that ALL POLYSACCHARIDES (such as glycogen) ARE NON-REDUCING SUGARS > I'm a Nursing Student. >M.J.T.M.E.
Will hydrolysed dextrine give positive response to Benedict test?
Yes, hydrolyzed dextrin will give a positive response to the Benedict test as it contains reducing sugars that can react with the Benedict's reagent to form a colored precipitate indicating the presence of reducing sugars.
Why Tollens reagent does not react with ketone?
Tollens reagent is a mild oxidizing agent that reacts with aldehydes to produce a silver mirror. Ketones, however, do not have a hydrogen atom bonded to the carbonyl group, making them resistant to oxidation by Tollens reagent. As a result, ketones do not react with Tollens reagent.
Why did the potato juice test negative in the benedict's reagent test?
The potato juice likely tested negative in the Benedict's reagent test because it does not contain reducing sugars, such as glucose or fructose, which are necessary to form a positive reaction with Benedict's reagent. Potatoes primarily consist of starch, a polysaccharide that is not a reducing sugar, explaining the negative test result.
What is a good conclusion of the benedicts test?
A good conclusion of the Benedict's test would be to state whether the test result was positive or negative for reducing sugars. Positive result would indicate the presence of reducing sugars, while a negative result would suggest their absence. This information can be important for further analysis or identification of certain carbohydrates.
Explain the chemical mechanism for detecting indole in a bacterial culture?
Indole can be detected in a bacterial culture by using Kovac's reagent, which reacts with indole to produce a red color. The chemical mechanism involves the reaction between the indole and the reagent, resulting in the formation of a red complex that can be visually observed. This test is commonly used in microbiology to differentiate between bacteria that can produce indole (positive result) and those that cannot (negative result).
Effect of formaldehyde to schiff's reagent?
Formaldehyde reacts with Schiff's reagent to produce a colorless complex, inhibiting its ability to detect aldehydes or ketones in tissues. This can interfere with the staining process in histology studies, preventing accurate visualization of certain cellular components.
An unknown sample is tested with both biuret reagent and benedicts reagent both test result in a blue color what has been learned and why are these called negative results?
The blue color observed with both the biuret and Benedict's reagents indicates that proteins are not present in the sample. These results are considered negative because they do not indicate the presence of proteins or reducing sugars, which the biuret and Benedict's tests are specifically designed to detect, respectively.
