e. Produces no color change with Benedict\'s or Seliwanoffs reagent, but blue-bl
ID: 1034321 • Letter: E
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e. Produces no color change with Benedict's or Seliwanoffs reagent, but blue-black color with iodine reagent E. Hydrolysis of Disaccharides and Polysaccharides Results Sucrose+ H,0 Sucrose+ HCI Starch+1H,O Sucrose+HC alua 2. Benedict's test ydrolysisBiue (Yes/No) ange o re s Questions and Problems 06 How do the results of the Benedict's test indicate that hydrolysis of sucroswe and starch occurred? Q7 How do the results of the iodine test indicate that hydrolysis of starch occurred? Indicate whether the following carbohydrates will give a positive (+) or a negative (-) result in each type of test listed below Q8 Benedict's Test Seliwanoffs Test Fermentation Test lodine Test 1 Glucose Fructose Galactose Sucrose Lactose Maltose Amylose -h Copyright O 2014 Pearson Education, Inc.Explanation / Answer
Hey there,
There are a total of 5 questions in the photograph. Your answers to all questions are quite acurate , so i assume that you need help with Q7 and Q8.
Next time, please mention the questions you need me to elaborate on. It really helps!
Now, lets get on to answers.
Q7) When hydrolysis occurs, starch is essentially broken down. This phenomenon can yield various saccharide molecules. Starch is a polymer of glucose, and hence a complete hydrolysis, would have yielded pure glucose . But due to several factors, intermediate products are formed. The common characteristic feature that separate starch from the hydrolysed products is that , starch gives a blue- black color on addition of iodine, while the products donot. The reason behind this fact is that, blue color is formed when Iodine is trapped in the spaces found between glucose molecules in starch. After hydrolysis, this is not possible as all starch molecules are consumed, and the interstitial spaces between product components are not sufficient to hold iodine any longer. Hence , the blue solution turns clear/ brown (clear if iodine concentration is less and brown otherwise). This isbhow a color change from blue to clear/brown indicate a hydrolysis.
Q8) Benedict test is answered if the compound is reducing sugar or in some cases if the easily hydrolysed product is reducing ( as in fructose).
Galactose is directly affected by benedict solution, giving an orange red color, due to the presence of free aldehyde group(reducing sugar). Hence test is positive.
In terms of seliwanoff's tests,
Galactose gives negative result, due to formation of large amounts of glucose , and seliwanoff's test is answered by ketohexoses, galactose not being one , doesn't answer the test.
Similarly, lactose, amylose and maltose gives negative results for seliwanoff's test as they are not keto hexoses.( Lactose is galactose+ glucose, maltose and amylose are 2 glucose molecules)
Fermentation tests: The fermentation test is used to determine whether a bacteria can utilize a certain carbohydrate or not . It tests for the presence of acid or gas produced from carbohydrate fermentation.
All carbohydrates at some point can be fermented. Hence the answer would lie on the basis of the test and conditions you choose for your experiment . Maltose, glucose, fructose and sucrose are readily fermented. While amylose , lactose and galactose can only be fermented by specific bacteria.
Iodine Test. It is answered only by helical poly-carbohydrates that can trap iodine. Hence, amylose being a polymer chain, gives positive test. All other species gives negative test.
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