I know so far that starch has an adehyde group but it is too small in comparison to the rest of its own molecule. The experiment used benedict's solution to determine wheter there was a reaction of glucose or not. Starch did not give a positive glucose test. Why?
2006-11-17 16:15:26 · 7 answers · asked by geniusflightnurse 4 in Science & Mathematics ➔ Chemistry
A starch molecule is made up of 100's of glucose monomers. And each glucose monomer in a starch is linked with another glucose monomer by alpha -1,4 linkage due to which a starch molecule does not have a free aldehyde group which is opresent in a free glucose molecule. At its end it may have a free aldehyde group, but is too small in amount to show the reaction in comparision to a huge glucose monomer. As Benedict's Test is a test to determine presence or absence of a aldehydic group; a starch molecule can not show a positive glucose test. But if a starch molecuse is hydrolysed with help of an acid or amylase enzyme it will certainly show hte positive glucose test.
2006-11-17 17:34:00 · answer #1 · answered by yogen p 2 · 1⤊ 0⤋
Starch did not give a positive test because starch is a complex sugar. Only simple sugars (such as glucose) will give a positive test when treated with Benedict's solution. I believe this is so as the reaction of the dyes in the Benedict's solution is dependant on the binding of the dye with the hydroxyl groups of the sugar. Starch contains sugars that have fewer free hydroxyl groups as the hydroxyl groups are the point of polymerization. If you treat the starch with amylase it will be broken down into a simple sugar and will then give a positive test when treated with the Benedict's solution. The test for starch is treatment with iodine, which will turn the starch a dark color upon treatment.
2006-11-17 16:37:03 · answer #2 · answered by mg 3 · 1⤊ 0⤋
Positive Glucose Test
2016-11-04 04:06:20 · answer #3 · answered by Anonymous · 0⤊ 0⤋
1
2016-05-18 23:53:38 · answer #4 · answered by ? 3 · 0⤊ 0⤋
Starch is essentially a long chain of glucoses in a 1-4 linkage. Reduction of sugars occurs at carbon 1, so in the entire starch polymer there is only one reduction which takes place. Benedicts might reduce a few sugars, but only a few. You need many thousands more to get any kind of observable change.
2006-11-17 16:52:06 · answer #5 · answered by Biznachos 4 · 0⤊ 0⤋
Probably both of them, starch is made out of glucose. Starch is just the way the energy is stored ;) Glucose (sugars) are made by photosynthesis so they will always be available and might form starch after they are made... so both im going for!
2016-05-22 00:17:31 · answer #6 · answered by Anonymous · 0⤊ 0⤋
My guess is that starch is a complex carbohydrate and glucose is a simple carb.
2006-11-17 16:33:28 · answer #7 · answered by kihela 3 · 0⤊ 0⤋