What carbohydrate(s) would have the following test results? Produces a reddish-o

Question

What carbohydrate(s) would have the following test results? Produces a reddish-orange solid with Benedict's and a red color with seliwanoff's reagent in I minute Gives a color change with Benedict's test, a light orange color with seliwanoff's reagent after 5 minutes, and produces no bubbles during fermentation Gives no color change with Benedict's or Seliwanoff's test, but turns a blue-black color with iodine reagent How do the results of the Benedict's test indicate that hydrolysis of sucrose and starch occurred? How do the results of the iodine test indicate that hydrolysis of starch occurred?

Explanation / Answer

5.

a) Ketose

b) Aldose

c) Starch

6) Benedict's solution contains copper, which can accept electrons from reducing sugars and change color. Since sucrose and starch are not reducing sugars, Benedict's test will be negative for them. However, the hydrolysis of sucrose produces glucose and fructose, both of which are reducing sugars. So, if sucrose has been hydrolyzed, there will be reducing sugars present which will react with Benedict's reagent to give a positive test. Similarly, hydrolysis of starch produces glucose which will react with Benedict's reagent to give a positive test.

7) An iodine solution turns a purplish-black if it comes into contact with a starch molecule. This reaction can take place at very minute concentrations of starch.

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