EXPERIMENT 4: Properties of Carbohydrates (Part 2)

Benedict's Test
Picric Acid Test
Moore's Test

Test for Reducing Sugars:

Benedict's Test

Is based on the fact that cupric ion (Cu2+) will oxidize aliphatic aldehydes, including a-hydroxyaldehydes such as aldoses.

cupric ion (Cu2+); aliphatic aldehydes

Benedict's test is based on the fact that _____ will oxidize _____, including a-hydroxyaldehydes such as aldoses.

a-hydroxyaldehydes; aldoses

Benedict's test is based on the fact that cupric ion (Cu2+) will oxidize aliphatic aldehydes, including ____ such as ____.

formation of a brick red precipitate of cuprous oxide (Cu2O)

Positive test for Benedict's Test

cuprous oxide (Cu2O)

Reduced product in benedict's test

Benedict's Test

A positive test is evidenced by the formation of a brick red precipitate of cuprous oxide (Cu2O), the reduced product.

red to orange to green

The color of the precipitate in Benedict's Test can vary from?

combination of blue solution and some orange precipitate

The green color precipitate in Benedict's Test is because of the?

Benedict's Test

Can also be used to quantitatively estimate the amount of sugar in a solution.

Benedict's Test

This is also used to detect glucose in the urine.

negative result

A blue solution in Benedict's test means?

Green/yellow ppt

This colored ppt in Benedict's test depict traces of reducing sugar present.

Orange red ppt

This colored ppt in Benedict's test depict a moderate amount of reducing sugar present.

Brick-red ppt

This colored ppt in Benedict's test depict a large amount of reducing sugar present.

Picric Acid Test

In this test, saturated picric acid solution (yellow) is used as an oxidizing agent

Picric Acid Test

Positive result is indicated by the formation of mahogany red colored solution

saturated picric acid solution (yellow)

Oxidizing agent in Picric Acid Test

yellow

What color is saturated picric acid solution?

10% Na2CO3

In the Picric Acid test, saturated picric acid solution (yellow) is used as an oxidizing agent. The environment is made alkaline by ______.

formation of mahogany red colored solution

Positive result in Picric Acid Test

reduction of picric acid to picramic acid

Positive result in Picric Acid Test is indicated by the formation of mahogany red colored solution which is due to the?

glucose

Example of a known reducing sugar that reacts with picric acid

Moore's Test

At basic environment, this carbonyl groups can undergo aldol condensation.

Moore's Test

For reducing sugars, the product is caramel with a brown color and characteristic odor. The odor is intensified when carefully acidified with diluted sulfuric acid.

reducing sugars

Have free carbonyl groups in their structure

free carbonyl groups

Reducing sugars have ______ in their structure

aldol condensation

As mentioned, reducing sugars have free carbonyl groups in their structure. At basic environment, this carbonyl groups can undergo ______.

caramel with a brown color and characteristic odor

For reducing sugars in Moore's Test, the product is?

diluted sulfuric acid

The odor of product in Moore's test is intensified when carefully acidified with _____.

Barfoed's Test for Monosaccharides

Like Benedict's test, this test depends on the reducing properties of sugars.

Barfoed's Test for Monosaccharides

Test for distinguishing between monosaccharides and disaccharides.

Barfoed's Test for Monosaccharides

The oxidizing agent used here is like Benedict's test which is cupric ion (Cu²).

Barfoed's Test for Monosaccharides

A positive test for monosaccharides is indicated by the formation of the brick red precipitate of Cu2O within 2-3 minutes. For reasons that are not fully understood, disaccharides require a longer time, providing the precipitate only after about 10 minutes

cupric ion (Cu2+)

The oxidizing agent used in Barfoed's Test

formation of the brick red precipitate of Cu₂O within 2-3 minutes

A positive test for monosaccharides in Barfoed's test

formation of the brick red precipitate of Cu₂O after about 10 minutes

A positive test for disaccharide in Barfoed's test

Seliwanoff's Test for Ketoses

Is used to distinguish aldoses from ketoses.

Seliwanoff's Test for Ketoses

The formation of cherry red solution after 2 minutes indicates a positive test in this test.

furfural derivatives.

Seliwanoff's reagent dehydrates ketoses more rapidly to give _______.

ketoses

Seliwanoff's reagent dehydrates ____ more rapidly to give furfural derivatives.

condensation

The resultant furfural derivatives undergo ____ reaction with resorcinol present in the reagent to give cherry red complex.

resorcinol

The resultant furfural derivatives undergo condensation reaction with _____ present in the reagent to give cherry red complex.

cherry red complex

The resultant furfural derivatives undergo condensation reaction with resorcinol present in the reagent to give ______.

formation of cherry red solution after 2 minutes

Indicates positive test in Seliwanoff's Test.

keto-containing carbohydrates

Seliwanoff's test will be answered by _______, whether monosaccharide or disaccharide.

Bial's Test for Pentoses

Test used to distinguish pentoses from hexoses.

Bial's Test for Pentoses

This test gives muddy-brown, yellow or gray solution.

bluish green solution

A pentose, if present in Bial's Test, will be dehydrated which then reacts with the orcinol and ferric ion to generate a ____.

orcinol and ferric ion

A pentose, if present in Bial's Test, will be dehydrated which then reacts with the ____ to generate a bluish green solution.

pentose

A ____, if present, will be dehydrated which then reacts with the orcinol and ferric ion to generate a bluish green solution.

Hexoses

_____ are also dehydrated but yield different products in Bial's test which when reacted with orcinol and ferric ion, gives muddy-brown, yellow or gray solution.

muddy-brown, yellow or gray solution

Hexoses are also dehydrated but yield different products which when reacted with orcinol and ferric ion, gives ______.

dehydration

What reaction is involved in Bial's test?

lodine Test for Polysaccharides

Is a very specific test for polysaccharides.

lodine Test for Polysaccharides

A color change of I2 in KI solution (the original color is brown) when added to a solution of carbohydrates indicates the presence of polysaccharides.

starch

Most polysaccharides have highly coiled structures, such as ___.

coiled structures

Most polysaccharides have highly ____, such as starch.

lodine

_____forms a coordinate complex between the helically coiled polysaccharide chain and iodine centrally located within the helix due to adsorption.

helically coiled polysaccharide chain; iodine

lodine forms a coordinate complex between the _____ and _____ centrally located within the helix due to adsorption.

adsorption

lodine forms a coordinate complex between the helically coiled polysaccharide chain and iodine centrally located within the helix due to _____.

brown

A color change of I2 in KI solution (the original color is ____) when added to a solution of carbohydrates indicates the presence of polysaccharides.

polysaccharides

A color change of I2 in KI solution (the original color is brown) when added to a solution of carbohydrates indicates the presence of _____.

color change of I2 in KI solution (the original color is brown)

Indicates positive test in Iodine test for polysaccharides

Barfoed's Test

Test for monosaccharides

monosaccharides

Barfoed's Test is a test for?

Seliwanoff's Test

Test for ketoses

ketoses

Seliwanoff's Test is a test for?

Bial's Test

Test for pentoses

pentoses

Bial's Test is a test for?

Iodine Test

Test for polysaccharides

polysaccharides

Iodine Test is a test for?

enediol

In Benedict’s test, when a reducing sugar is subjected to heat in the presence of an alkali, it gets converted into an ______ (which is a relatively powerful reducing agent).

cuprous ions (Cu+)

Therefore, when reducing sugars are present in the analyte, the cupric ions (Cu2+) in Benedict’s reagent are reduced to?

copper (I) oxide

These cuprous ions form ______ with the reaction mixture and precipitate out as a brick-red colored compound.

brick-red

These cuprous ions form copper(I) oxide with the reaction mixture and precipitate out as a _____ colored compound.

Blue solution in Benedict’s test

No reducing sugar

0 g%

Green solution in Benedict’s test

Trace Reducing Sugar

< 0.5 g%

Green ppt in Benedict’s Test

Trace Reducing Sugar

0.5 - 1 g%

Yellow ppt in Benedict’s Test

Low Reducing Sugar

1 - 1.5 g%

Orange Red ppt in Benedict’s Test

Moderate Reducing Sugar

1.5 - 2 g%

Brick Red ppt in Benedict’s Test

High Reducing Sugar

> 2 g%

aldonic acid and mahogany-red precipitate (picramic acid)

When a reducing sugar reacts with picric acid, it is converted into its corresponding _______________ is produced indicating a positive result.

Blue

Resulting Color of Starch with I2 in KI solution

Reddish-brown

Resulting Color of Glycogen with I2 in KI solution

Brown

Resulting Color of Innulin with I2 in KI solution

Colorless

Resulting Color of Cellulose with I2 in KI solution