Benedict's Test and acid hydrolysis

Good morning, I am hoping someone can tell me if my observations are correct as my brain is frazzled today!
What effect does acid hydrolysis have on a glucose sample? My glucose tested positive with Benedict's, but following acid hydrolysis there was a negative Benedict's test. Is this correct. I am getting the correct results from the sucrose sample, and the sucrose/low glucose sample, but I've not thought about what happens to the glucose. Someone please tell me that this is correct, and that I don't need to start again from scratch.
Thanks in advance.
 

Peter Sigsworth

COMMITTEE
Good morning, I am hoping someone can tell me if my observations are correct as my brain is frazzled today!
What effect does acid hydrolysis have on a glucose sample? My glucose tested positive with Benedict's, but following acid hydrolysis there was a negative Benedict's test. Is this correct. I am getting the correct results from the sucrose sample, and the sucrose/low glucose sample, but I've not thought about what happens to the glucose. Someone please tell me that this is correct, and that I don't need to start again from scratch.
Thanks in advance.
Are you neutralising the acid with bicarb before the benedict's test?
 
Yes, all neutralised.
Maybe you are making something else.
Does glucose react with acid?
Image result for glucose + acid
Each of the OH groups on glucose could be reversibly protonated by strong acids just like the OH group in the methanol molecule above. ... For the cyclic isomers of glucose, one hydroxy group is unique. This is the one derived from nucleophilic attack on the aldehyde functional group.
 

Peter Sigsworth

COMMITTEE
mmmm. The acid shouldn't effect the glucose - If it hydrolyses the sucrose to reducing sugars which test positive then it shouldn't futher effect the reducing sugars?
 
follow this link (https://www.google.com/search?q=tes...active&ssui=on#kpvalbx=_WRFDYYygFo_aUu-GtGg33)

You would only hydrolyise if the reducing sugar test is negative anyway - there would be no need/reason to add acid to a reducing sugar.
This is why I have never experienced it before, as you generally don't test a sample that has already tested positive for reducing sugars. I can see what you are saying, if the acid hydrolyses glucose to something else, it would do the same to the glucose produced from the acid hydrolysis of sucrose. Perhaps this does happen if the sucrose sample is acid hydrolysed for a longer period of time.
Anyway, I've explained my observation to the teacher carrying out the practical, so at least he knows what to expect.
 
Top