lab activity 2 reducing & non-reducing sugars iug, 2015 dr. tarek zaida iug, 2015 dr. tarek...

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Lab Activity 2 Reducing & Non-reducing Sugars IUG, 2015 Dr. Tarek Zaida

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Page 1: Lab Activity 2 Reducing & Non-reducing Sugars IUG, 2015 Dr. Tarek Zaida IUG, 2015 Dr. Tarek Zaida

Lab Activity 2Reducing & Non-reducing Sugars

IUG, 2015Dr. Tarek Zaida

Page 2: Lab Activity 2 Reducing & Non-reducing Sugars IUG, 2015 Dr. Tarek Zaida IUG, 2015 Dr. Tarek Zaida

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Reducing- & Non-reducing Sugars

Sugars

Open-chain C=O

Closed-ringCarbonyl C

attached to O of ring & -OH

Page 3: Lab Activity 2 Reducing & Non-reducing Sugars IUG, 2015 Dr. Tarek Zaida IUG, 2015 Dr. Tarek Zaida

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Reducing sugars• Oxidized by mild oxidizing agents

Non-reducing sugars• Not oxidized by mild oxidizing

agents

Page 4: Lab Activity 2 Reducing & Non-reducing Sugars IUG, 2015 Dr. Tarek Zaida IUG, 2015 Dr. Tarek Zaida

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• All monosaccharides• Maltose, LactoseReducing

sugars

• SucroseNon-reducing

sugars

Page 5: Lab Activity 2 Reducing & Non-reducing Sugars IUG, 2015 Dr. Tarek Zaida IUG, 2015 Dr. Tarek Zaida

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Common Oxidizing Agents

Benedict’s sol. Fehling’s sol. Tollen’s reagent

Page 6: Lab Activity 2 Reducing & Non-reducing Sugars IUG, 2015 Dr. Tarek Zaida IUG, 2015 Dr. Tarek Zaida

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Oxidizing Reagent Benedict's Solution Fehling's Solution Tollen's Reagent

Composition copper sulfate in

alkaline citrate

copper sulfate in alkaline

tartrate

silver nitrate in aqueous

ammonia

Color of Solution deep blue deep blue colorless

Color After Reaction with a

Reducing Sugar

brick red precipitate

Cu2O(s)

brick red precipitate

Cu2O(s)

silver mirror forms

Ag(s)

Species Being Reduced

(the oxidant)

Cu2+

Cu2+ + e ---> Cu+

Cu2+

Cu2+ + e ---> Cu+

Ag+

Ag+ + e ---> Ag(s)

Species Being Oxidized

(the reductant)

reducing sugar

oxidized to carboxylate

reducing sugar

oxidized to carboxylate

reducing sugar

oxidized to carboxylate

Page 7: Lab Activity 2 Reducing & Non-reducing Sugars IUG, 2015 Dr. Tarek Zaida IUG, 2015 Dr. Tarek Zaida

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In-lab ExperimentsBe

nedi

ct’s

Test

For

red

ucin

g su

gars

Barf

oed’

s Te

st fo

r mon

osac

char

ides

Picr

ic A

cid

Test

For r

educ

ing

suga

rs

Page 8: Lab Activity 2 Reducing & Non-reducing Sugars IUG, 2015 Dr. Tarek Zaida IUG, 2015 Dr. Tarek Zaida

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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 precipitateRCHO + 2Cu2+ + 4OH- ----> RCOOH + Cu2O + 2H2O

Page 9: Lab Activity 2 Reducing & Non-reducing Sugars IUG, 2015 Dr. Tarek Zaida IUG, 2015 Dr. Tarek Zaida

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Reagents

• Set up 1 % solutions of: glucose, sucrose, starch, maltose, fructose, lactose.• Benedict's reagent (ready to use)

Page 10: Lab Activity 2 Reducing & Non-reducing Sugars IUG, 2015 Dr. Tarek Zaida IUG, 2015 Dr. Tarek Zaida

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Procedure

1. Place 15 drops of the following 1% carbohydrate solutions in separate, labeled test tubes: glucose, fructose, sucrose, lactose, maltose, and starch.

2. Also place 1 ml of distilled water in another tube to serve as a control.

3. To each tube, add 1 ml of Benedict's reagent and heat the tubes in a boiling water bath for 5 minutes.

4. 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.

Page 11: Lab Activity 2 Reducing & Non-reducing Sugars IUG, 2015 Dr. Tarek Zaida IUG, 2015 Dr. Tarek Zaida

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2. Barfoed's Test(Used to distinguish between mono- & di-saccharides)

• PrincipleBarfoed's reagent reacts with mono-saccharides to produce cuprous oxide at a faster rate than disaccharides do:

• RCHO + 2Cu2+ + 2H2O -----> RCOOH + Cu2O + 4H+

Page 12: Lab Activity 2 Reducing & Non-reducing Sugars IUG, 2015 Dr. Tarek Zaida IUG, 2015 Dr. Tarek Zaida

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Reagents

Set up 1 % solutions of the following solutions separately:

• glucose, • maltose, • fructose, • lactose, • sucrose• Barfoed's reagent.

Page 13: Lab Activity 2 Reducing & Non-reducing Sugars IUG, 2015 Dr. Tarek Zaida IUG, 2015 Dr. Tarek Zaida

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Procedure

• 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.

Page 14: Lab Activity 2 Reducing & Non-reducing Sugars IUG, 2015 Dr. Tarek Zaida IUG, 2015 Dr. Tarek Zaida

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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

Page 15: Lab Activity 2 Reducing & Non-reducing Sugars IUG, 2015 Dr. Tarek Zaida IUG, 2015 Dr. Tarek Zaida

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Reagents

• Set up 1 % solution of: • maltose, • sucrose• Saturated solution of picric acid• 1N NaOH solution

Page 16: Lab Activity 2 Reducing & Non-reducing Sugars IUG, 2015 Dr. Tarek Zaida IUG, 2015 Dr. Tarek Zaida

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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.

Page 17: Lab Activity 2 Reducing & Non-reducing Sugars IUG, 2015 Dr. Tarek Zaida IUG, 2015 Dr. Tarek Zaida

4. Tollen’s Test (Silver Mirror)

• Is used to test for the presence of aldehydes. In this reaction, an aldehyde is oxidized to a carboxylic acid while the Ag+ is reduced to silver metal, which deposits as a thin film on the inner surface of the glass. The reaction is as follows:

Page 18: Lab Activity 2 Reducing & Non-reducing Sugars IUG, 2015 Dr. Tarek Zaida IUG, 2015 Dr. Tarek Zaida

Materials:0.1 M AgNO3 0.8 M KOH

0.5 M Dextrose Large test tube/rubber stopper

Conc. HNO3 Beaker

Conc. NH4OH Deionized water

Prepare Tollen’s reagent as follows: Add 50 mL of 0.1 M AgNO3 to the beaker and add NH4OH to this. A brown precipitate will form. Continue adding NH4OH until the

solution becomes clear. To this, add 25 mL of 0.8M KOH. Again, add NH4OH until solution becomes clear.

Page 19: Lab Activity 2 Reducing & Non-reducing Sugars IUG, 2015 Dr. Tarek Zaida IUG, 2015 Dr. Tarek Zaida

Procedure

1. Clean the test tube to be used by rinsing with concentrated nitric acid and washing well with hot water.

2. Add 1 mL of sample solution to the test tube3. To this add 5 mL of Tollen’s reagent.

The solution will turn yellow and brown then become cloudy and dark before silver begins to form on the inside of the test tube. This should take a couple of minutes.

4. Remove the contents from the test tube and rinse the tube with water.The tube with a “silver mirror” can now be observed.