reactions of reducing and non-reducing sugars lab 2
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Reactions of Reducing and non-reducing sugars Lab 2. Alaa S Baraka Islamic university of Gaza. Reducing and Non-reducing sugars. Oxidation: loss of electrons Reduction: gain of electrons reducing sugars : - PowerPoint PPT PresentationTRANSCRIPT
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Reactions of Reducing Reactions of Reducing and non-reducing and non-reducing
sugarssugarsLab 2Lab 2
Alaa S BarakaAlaa S BarakaIslamic university of Islamic university of GazaGaza
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Reducing and Non-reducing Reducing and Non-reducing sugarssugars
Oxidation: loss of electronsOxidation: loss of electrons Reduction: gain of electronsReduction: gain of electronsreducing sugarsreducing sugars::Sugars that can be oxidized by mild
oxidizing agents and the oxidizing agent is reduced in the reaction.
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Reducing and Non-reducing Reducing and Non-reducing sugarssugars
A non-reducing sugars: A non-reducing sugars: sugars that not oxidized by mild oxidizing agents.
Sugars exist in solution as an equilibrium mixture of open-chain and closed-ring (or cyclic) structures.
All monosaccharides have an open and closed form structure,but oligosaccharides have only closed structure..
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Opend and closed form of Opend and closed form of monosaccaridesmonosaccarides
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The active part in sugars is aldehyde or The active part in sugars is aldehyde or ketone groupketone group..
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Lactose is reducing sugar( one of the carbonyle groups are free) as shown:
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Sucrose is non-reducing sugar(the carbonyle groups are busy in the to side) as shown:
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Starch and polysaccharides Starch and polysaccharides are non-reducing sugarsare non-reducing sugars
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Common oxidizing agents used to Common oxidizing agents used to test for the presence of a reducing test for the presence of a reducing sugar are: Benedict's solution, sugar are: Benedict's solution, Fehling's solution and picric acid Fehling's solution and picric acid solutionsolution..
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Think, and suggested, in Think, and suggested, in practical life,,,,, how you can practical life,,,,, how you can
take advantage of ittake advantage of it ?? ??
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In-lab Experiments
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1 .Benedict's Test(positive for reducing sugars)
Principle: Benedict's reagent contains
cupric ions, which in an alkaline environment, oxidize the aldehyde group to a carboxylic acid. Cupric ions are reduced to cuprous oxide, which forms a red precipitate
RCHO + 2Cu2+ + 4OH- ----> RCOOH + Cu2O + 2H2O
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Reagents Set up 1 % solutions of: glucose, sucrose, starch, maltose, fructose, lactose. Benedict's reagent (ready to use)
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Procedure Place 15 drops of the following 1%
carbohydrate solutions in separate, labeled test tubes: glucose, fructose, sucrose, lactose, maltose, and starch.
Also place 1 ml of distilled water in another tube to serve as a control.
To each tube, add 1 ml of Benedict's reagent and heat the tubes in a boiling water bath for 5 minutes.
Remove the tubes from water bath. Note and record the results.
In the presence of a reducing sugar a precipitate which may be red, yellow or green will form.
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2. Barfoed's Test(Used to distinguish between mono- &
di-saccharides) Principle Barfoed's reagent reacts with mono-
saccharides to produce cuprous oxide at a faster rate than disaccharides do:
RCHO + 2Cu2+ + 2H2O -----> RCOOH + Cu2O + 4H+
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Reagents Set up 1 % solutions of the
following solutions separately: glucose, maltose, fructose, lactose, sucrose Barfoed's reagent.
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Procedure 1. Place 15 drops of the following 1%
carbohydrate solutions in separate, labeled test tubes: glucose, fructose, sucrose, lactose, and maltose.
2. To each tube, add 1 ml of Barfoed's reagent, and heat in a boiling water bath for 10 minutes.
3. Remove the tubes from water bath. Note and record your observations.
A red precipitate will form if the test is positive.
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3.Picric Acid Test(for reducing sugars)
Principle Picric acid (2,4,6-trinitrophenol) or
TNP reacts with reducing sugars to give a red colored picramic acid C6H2.OH.NH2(NO2)2
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Reagents Set up 1 % solution of: maltose, sucrose Saturated solution of picric acid 1N NaOH solution
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Procedure 1. Into a test tube add 1 ml of maltose
solution, into the second tube, 1ml of sucrose solution.
2. Add into each tube 1 ml of a saturated solution of picric acid, and then add into each tube 0.5 ml of sodium hydroxide solution.
3. Heat both samples in a boiling water bath. In the presence of reducing sugars, the
solution stains red; a sodium salt of picric acid is formed.