Qualitative Analysis of Carbohydrates Flashcards
skeletons of
covalently bonded carbon atoms
organic compounds
are the
major components of cells and tissues
organic compounds
They provide energy for life processes, participate and
regulate metabolic reactions, and transmit information
organic compounds
Organic molecules in living organisms
can be classified either
carbohydrates
proteins
lipids
nucleic acids
are compounds that contain carbon, hydrogen and oxygen.
carbohydrates
includes a variety of compounds such as sugars, starches and cellulose.
carbohydrates
serve as energy sources for cells, while cellulose are structural components of the walls that
surround plant cells
what compounds (2)
sugars
starches
carbohydrates that have one sugar molecule
monosaccharides
carbohydrates with two sugar molecules
dissacharides
carbohydrates with many sugar unts
polysaccharides
is a chemical test which is used to check for the presence of carbohydrates in a given analyte
Molisch’s test
a solution of α-naphthol in ethanol
Molisch’s reagent
involves the addition of a solution of α-naphthol in ethanol to the analyte and the subsequent addition of a few drops of concentrated H2SO4 to the mixture
Molisch’s test
Molisch’s test reagents (2)
H2SO4 (sulfuric acid)
α-naphthol in ethanol
The formation of a ___or a ____-red ___at the point of contact between the H2SO4 and the analyte + Molisch’s reagent mixture confirms the presence of carbohydrates in the analyte.
purple
purplish-red
A positive reaction for Molisch’s test is given by almost all carbohydrates but exceptions
tetrose
triose
some compounds aside from carbohydrates that give positive results for Molisch’s test
glycoproteins
nucleic acids
tend to undergo hydrolysis when exposed to strong mineral acids and form monosaccharides
glycoproteins
nucleic acids
In Molisch’s test, the carbohydrate (if present) undergoes dehydration upon the introduction of concentrated hydrochloric or sulphuric acid, resulting in the formation of an ____
aldehyde
undergoes condensation along with two phenol-type molecules (such as α-naphthol, resorcinol, and thymol), resulting in the formation of a purple or reddish-purple coloured complex.
What kind of compound formed in molisch’s test
aldehydes
study the molisch’s test principle
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Molisch’s teast procedure
- Add 2 drops of Molisch reagent (prepared by dissolving 0.1g of ∞napthol in 2 mL of
ethanol) to 2 mL of sugar solution (glucose, fructose, galactose, sucrose, maltose,
lactose, starch) and mix. - Incline the tube, and gently add 2 mL of concentrated sulfuric acid down the side of
the test tube. - A purple color at the interface between the sugar and acid indicates a positive result.
is a chemical test that can be used to check for the presence of reducing sugars
in a given sample
Benedict’s test
compounds that Benedict test can be used to dientify
free ketone/aldehyde
complex mixture of sodium citrate,
sodium carbonate, and the pentahydrate of copper(II) sulfate
Benedict’s solution
what is Benedict’s solution made up of (3)
sodium citrate
sodium carbonate
copper (II) sulfate
All those carbohydrates which contain a free aldehyde or Ketonic group and reduce Fehling’s solution and Tollen’s reagent are referred as a
reducing sugar
galactose, glucose, glyceraldehyde, fructose, ribose, and xylose
examples are
reducing sugar
When exposed to ____ sugars, the reactions undergone by Benedict’s reagent result in the
formation of a brick-red precipitate, which indicates a positive Benedict’s test
reducing
When a reducing sugar is subjected to heat in the presence of an alkali, it gets converted into
an ___
enediol
Therefore, when reducing sugars
are present in the analyte, the cupric ions (Cu2+) in Benedict’s reagent are reduced to ___ ions
cuprous (Cu+)
reagent that can be prepared by mixing 17.3 grams of copper sulfate
pentahydrate (CuSO4.5H2O), 100 grams of sodium carbonate (Na2CO3), and 173 grams of
sodium citrate in distilled water (required quantity).
Benedict’s reagent
acts a source
of Cu
2+ ions in Benedict’s reagent
copper sulfate
in Benedcit’s reagent, provides an alkaline medium
sodium carbonate
review the results of Benedict’s test based on color
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can also be used to check for the presence of glucose in a
urine sample since this test detects any aldehydes and α-hydroxy ketones and glucose is an
aldose whose open-chain forms an aldehyde group, the test yields a positive result when
glucose is present in the analyte
Benedict’s test
However, a positive reaction can also be given by the
presence of ___ ____ in urine
ascorbic acid
homogentisic acid
False positive reactions may also be obtained if certain drugs are present, e.g. salicylates,
penicillin, streptomycin, isoniazid, and p-aminosalicyclic acid.
what kind of test
Benedict’s test
Chemicals present in a concentrated urine which may reduce Benedict’s reaction include
creatinine
urate
ascorbic acid
Benedict’s test procedure
- Add 1 mL of the 2% sugar solution (glucose, fructose, galactose, sucrose, maltose,
lactose, starch) to 5 mL of Benedict’s solution (prepared by mixing 10 g sodium
carbonate and 17.3 g monosodium citrate dehydrate in 85 mL water, and while
stirring add 10 mL of water containing 1.73 g copper sulfate then to a final volume of
100 mL). - Place test tubes in a boiling water bath.
- Formation of red to brick precipitate is a positive result.
an be defined as the most important complex carbohydrate compounds. It is a polysaccharide and glucoside reserve of plants. It is a renewable and biodegradable product, so it can act as a perfect raw material and a substitute for fossil-fuel components in making detergents, glues, plastics, etc.
starch
comprise a large number of glucose units that are bound together by glycosidic bonds and are produced by all vegetables and other plant sources through the process of photosynthesis.
starch
performed to test the presence of carbohydrates/starch
iodine test
is a chemical test used to distinguish mono- or disaccharides from certain polysaccharides like amylase, dextrin, and glycogen.
iodine test
based on the fact that polyiodide ions form colored adsorption complex with helical chains of glucose residue of amylase (blue-black), dextrin (black), or glycogen (reddish-brown).
iodine test
what compounds remain colorless in iodine test (3)
monosaccharides
disaccharides
branched polysaccharides (e.g. cellulose)
produces an orange-yellow hue in iodine test
amylopectin
aqueous solution of elemental iodine and potassium iodide
Lugol’s iodine
on its own is insoluble in water
Iodine
Addition of potassium iodine results in a reversible reaction of the iodine ion with iodine to form a
triiodide ion
The appearance of blue-black or purple color represents a ___ test, indicating the presence of start
positive
This test cannot be performed under acidic conditions as the starch hydrolyses under such circumstances
acidic conditions
iodine test procedures
- Add 2-3 drops of Lugol/s iodine solution or (pepared by dissolving 1g of iodine and 2
g potassium iodide in 100 mL distilled water) to 5 mL of 2% sugar solution (glucose,
fructose, galactose, sucrose, maltose, lactose, starch). - Starch gives a blue-black color.
is a chemical test used for detecting the presence of monosaccharides.
Barfoed’s test
reduction of cupric (II) acetate to cuprous (I) oxide (Cu2O),
Barfoed’s test
forms a brick-red precipitate when positive
Barfoed’s test
may react, but the reaction is much slower because they have to get hydrolyzed first and then react with the reagent cupric acetate to produce cuprous oxide
Disaccharides
brick red precipitate in Barfoed’s test
curpous (I) oxide (Cu2O)
This test is used to distinguish reducing monosaccharides from disaccharides by controlling pH and the time of heating.
Barfoed’s test
If a red precipitate is formed within two minutes, it means that a ____is present. If the red precipitate is formed after ten minutes of heating, a ___is present.
monosaccharides
disaccharides
Barfoed’s reagent is similar to Benedict’s reagent except that the pH is lower/higher (around 4.5), and the heating time is reduced to two minutes.
lower
____test would determine if the sample is a reducing sugar, and ____test would determine if it is a monosaccharide or disaccharide.
Benedict’s test
Barfoed’s test
Barfoed’s reagent is composed of
(2)
copper acetate monohydrate
glacial acetic acid
Barfoed’s reagent
- Add 1 mL of the 2% sugar solution (glucose, fructose, galactose, sucrose, maltose,
lactose, starch) to 3 mL of Barfoed’s reagent (Mix 7 g of copper acetate monohydrate
with 1 mL of glacial acetic acid in distilled water and make the final volume 100
mL). - Place test tubes into boiling water bath and heat for 3-10 minutes. Remove the tubes
from the bath and allow cooling. - Formation of scanty red precipitate is a positive result.
is used to differentiate between sugars that have a ketone group (ketose) and sugars that have an aldehyde group (aldoses).
Seliwanoff’s test
Seliwanoff’s reagent consists of
resorcinol
concentrated HCl
are more rapidly dehydrated than aldoses
ketoses
Ketoses undergo dehydration in the presence of concentrated acid to yield
5-hydroxymethy furfural
complex produced when dehydrated ketose reacts with two equivalents of resorcinol in series of condensation reactions
xanthenoid
deep cherry red complex seen in positive seliwanoff’s test
xanthenoid
Other carbohydrates like sucrose and inulin also give a positive result for this test as these are hydrolyzed by acid to give ___
fructose
is used in the method for the colorimetric determination of fructose in fermentation media.
Selifwanoff’s color reaction
Seliwanoff’s test procedures
- Add 1 mL of 1% sugar solution (glucose, fructose, galactose, sucrose, maltose,
lactose, starch) to 10 mL of the reagent (Dissolve 0.1 g resorcinol in 33 mL
concentrated hydrochloric acid (HCl) and make the final volume of 100 mL). - Heat the solution in boiling water bath for 5 minutes.
- A deep cherry or red color within 5 minutes is a positive result.
Silver mirror test (Tollen’s reagent) procedures
- Wash the tube with a 10% solution of sodium hydroxide (1g NaOH in 10 mL distilled
water). - Add 2 mL of a 5% (0.5g in 10 mL distilled water) silver nitrate solution (AgNO3) into
the washed tube, then add one drop of the 10% sodium hydroxide solution. - Add one drop of 28% ammonia solution (add more drops if necessary). Shake
constantly until silver oxide dissolves, then add 1 mL of 2% sugar solution. - The formation of a silver mirror in the inner surface of the test tube is a positive
result.
is a qualitative laboratory test used to distinguish between an aldehyde and a ketone by exploiting the fact that aldehydes are readily oxidized
Tollens’ test
Tollen’s reagent is composed of
alkaline silver nitrate
aqueous ammonia
alkaline silver nitrate chemical formula
AgNo3
aqueous ammonia solution
NH4OH
The reaction is accompanied by the reduction of silver ions into metallic silver
Tollen’s test
must be worn all the time inside the laboratory and especially
when handling the following chemicals
protective gloves
may cause liver, kidney damage, blood abnormalities, and severe eye
irritation
1-Naphthol
is extremely corrosive and can cause serious
burns when not handled properly
Sulfuric acid
(may cause eye and skin irritation
resorcinol
may explode if heated. Causes severe skin burns
Ammonia
If swallowed, causes severe irritation and chemical burns to the
gastrointestinal tract, and can cause permanent eye damage/blindness
Sodium hydroxide
study the table for positive reactions in sugar solution
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most abundant organic compounds found in living organisms
carbohydrates
carbohydrates is composed of
Carbon, Hydrogen, and Oxygen
act as the primary source to provide energy for functioning of living organisms
carbohydrates
considered as hydrates of carbon
carbohydrates
called saccharides
carbohydrates
carbohydrates are what
polyhydroxy aldheydes or polyhydeoxy ketones
polyhydroxy aldehydes and ketones and their anhydrides
carbohydrates
contain potentially active aldehydes or ketone groups and their derivatives
carbohydrates
carbohydrates can be represented by stoichiometric formula
(CH2O)n
is characterized by the presence of fructose in the urine after ingesting fructose. It arises as a result of a deficiency of the hepatic enzyme fructokinase and is an autosomal recessive genetic disorder.
fructosuria
- Urine galactose can be elevated in patients with galactosemia caused by either GALT deficiency or galactokinase deficiency
galactosuria
cannot be hydroylzed into simpler carbohydrates
monosaccharides
monosaccharides can be classified into based on number of carbon atoms present
triose
tetrose
pentose
hexose
heptose
carbohydrates classified based on the functional group present
aldose
ketose
example of monosaccharides
xylose
glucose
galactose
fructose
give rise to two monosaccharide units upon hydrolysis
disaccharides
formed when two monosaccharides undergo a condensation reaction
disaccharides
reaction that involves the elimiation of a small molecule, such as water, from the functional groups only
disaccharides
polymeric carbohydrate structures, formed of repeating units of either monosaccharides or disaccharides joined together by glycosidic bonds
polysaccharides
monosaccharides + disaccharides forming polysaccharides are joined together by what bond
glycosidic bond
contain more than 10 monosaccharide units
polysaccharide
primary function of polysaccharides
energy storage
food reserve
3 important polysaccharides
starch, glycogen, cellulose
monosaccharide that contains only one aldehyde group per molecule
aldose
monosaccharide that contains only one ketone group per molecule
ketose
monosaccharide that contains five carbon atoms
pentose
monosaccharide that contains five carbon atoms
pentoses
hexose with an aldehyde group on one end
aldohexose
ketone-containing hexose
ketohexose
a polysaccharide
amylose
a straight chain polymer of D-glucose units
amylose
constitutes about 20% of the starch
amylose
a polysaccharide that has a branched biopolymer consisting of linear chains of glucose residues
glycogen
the principal storage form of glucose in animal and human cells
glycogen
a polysaccharide
consists of a linear chain of β(1→4) linked D-glucose units
cellulose
an important structural component of the primary cell wall of green plants
cellulose
a monosaccharide
contains five carbon atoms (pentose), a formyl and aldehyde functional group
xylose
xylose is what (aldose,ketose, hexose,pentose)
aldopentose
a monosaccharide
contains six carbon atoms (hexose) and an aldehyde functional group (aldose).
Aldohexose
widely used aldohexose in living organisms
glucose
a monosaccharide
contains six carbon atoms (hexose) and an aldehyde functional group (aldose)
Aldohexose
not normally found in nature but it is mostly hydrolyzed from lactose
galactose
monosaccharide
contains six carbon atoms (hexose) and a ketone functional group (ketose)
Ketohexose
Also known as levulose
fructose
fructose is also known as
levulose
a disaccharide
contains the units of galactose and glucose
lactose
a disaccharide
contains two units of glucose
maltose
a disaccharide
contains the units of glucose and fructose. commonly referred to as "table sugar"
sucrose
sucrose is commonly referred to as
table sugar
Some Important Tests for the Detection of Carbohydrates
Molish Test
Fehling’s Test
Benedict’s Test
Tollen’s test
Iodine Test
used to detect the presence of carbohydrates in different samples.
Molisch’s test
can be used to detect the formation of carbohydrates as a by-product in different reactions and distinguish it from other biomolecules.
Molisch test
A test for all carbohydrates.
Indicates presence of a carbohydrate
Molisch test
in Molisch test, which give a rapid positive test while these other saccharides react slower
Monosaccharides give a rapid positive test.
Disaccharides and polysaccharides react slower
Principle of Molisch test
Hydrolysis of carbohydrates to ____ form
monosaccharide
Principle of Molisch test
Dehydration of monosaccharide to ___ derivatives
furfural
When carbohydrates are exposed to concentrated H2SO4, they undergo dehydration to form
furaldehyde derivatives
pentoses when reacting with H2SO4 form
furfural
hexoses form what when reacting with H2SO4
hydromethyl furfural
what reagent does carbohydrate condenses with to form a colored interphase
a-naphthol
The formation of the purple colored ring occurs at the interface between the ____ ___and the test solution.
sulfuric acid
remains above the test solution as the acid is denser than the test solution in Molisch’s test
Sulfuric acid
Molisch test is positive for what
carbohydrates
reagents of Molisch test
a-naphthol and 95% ethanol
chemical analytical method used for the detection of reducing sugar in a solution.
benedict’s test
a qualitative test often used for the differentiation of carbohydrates (saccharides/sugars) into reducing and non-reducing types.
benedict’s test
It is widely used to identify monosaccharides (simple sugars) and other reducing sugars
Benedict’s test
Benedict’s test is used as an alternative to
Fehling’s test
To detect the presence of reducing sugar in the sample solution
To diagnose diabetes mellitus by detecting glucose in the urine sample
To estimate the concentration of reducing sugar in the sample solution
To differentiate and identify the extracted carbohydrates
what test
Benedict’s test
Carbohydrates with a free aldehyde or keto group have the ability to reduce various metallic ions.
what test
Beenedict’s test
In this test, ___ ions are reduced to ___ions by the ____formed from sugars in the alkaline medium of Benedict’s reagent.
Cupric
Cuprous
Enediols
Benedict’s test Result interpretation based on color
Blue
Green
Green ppt.
Yellow ppt.
Orange ppt.
Brick red ppt.
B - No reducing sugar
G - trace reducing sugar (<0.5g%)
GPPT- trace reducing sugar (0.5-1%)
YPPT - low reducing sugar (1-1.5g%)
OPPT - moderate reducing sugar (1.5-2g%)
RPPT - high reducing sugar (>2g%)
what disaccharide is positive for benedict’s test
lactose
maltose
Benedict’s reagent
Copper sulphate, sodium citrate and sodium carbonate
positive for benedict’s test is indicated by
brick red precipitate
dissociate to give sufficient cupric ions (in the form of cupric hydroxide) for the reduction reactions to occur.
copper sulfate
keeps the cupric hydroxide in solution without getting precipitated
sodium citrate
ake the pH of the medium alkaline
sodium carbonate
In the alkaline medium, sugars form ___ which are powerful ___agents.
enediols
reducing
reduce blue cupric hydroxide to insoluble yellow to red cuprous oxide in Benedict’s test
Enediols
a chemical test used to distinguish mono- or disaccharides from certain polysaccharides like amylase, dextrin, and glycogen.
Iodine test
a test for polysaccharides
Iodine test
To detect the presence of polysaccharides, primarily starch.
This test is used to detect the presence of starch in various samples.
Similarly, this test is performed to test the process of photosynthesis in plants.
what test
iodine test
forms a coordinate complex between the helically coiled polysaccharide chain and iodine centrally located within the helix due to adsorption
iodine
The color obtained depends upon the ___ of the unbranched or linear chain available for complex formation in Iodine test
length
The appearance of blue-black or purple color represents a ___ test, indicating the presence of starch.
positive
iodine test is a positive for what
amylose
deep blue color
reagents of Iodine test
2% solution of KI in water with few crystals of iodine
is a chemical test used to detect the presence of monosaccharides which detects reducing monosaccharides in the presence of disaccharides.
Barfoed’s test
To detect reducing carbohydrates.
To distinguish reducing monosaccharides from disaccharides.
what test
Barfoed’s test
This test is used to identify reducing monosaccharides and distinguish the reducing disaccharides from reducing monosaccharides.
what test
Barfoed’s test
Barfoed’s test determines the presence of reducing sugars. Aldoses and Ketoses can reduce cupric ions (II) to cupric oxide (I) even in ___ conditions
acidic
This test also distinguishes monosaccharides from disaccharides by what factor
controlling pH
time of heating
react very fast (within 3-5 mins) in Barfoed’s test
monosaccharides
react very slowly (more than 5 mins) in Barfoed’s test
Disaccharides
The presence of red precipitate detects the presence of reducing ____ in the sample.
Barfoed’s test
monosaccharides
If the color appears within the first few minutes, the sample contains reducing monosaccharides.
what test
Barfoed’s test
However, if the color appears later than the first 3 minutes, the sample is of reducing disaccharides.
what test
Barfoed’s test
A test to distinguish ketoses from aldoses in carbohydrates.
Resorcinol (Seliwanoff)’s test
identifies ketoses since the reaction occurs fast with ketoses.
Resorcinol (Seliwanoff’s) Test
also react but at much slower rate. in Seliwanoff’s test
aldose sugars
To detect the presence of ketohexoses in a given sample.
To distinguish ketoses from aldoses.
what test
Resorcinol (Seliwanoff’s test)
is used in the method for the colorimetric determination of fructose in fermentation media
Seliwanoff’s color reaction
A modified version of this test can be used for the determination of the concentration of ketoses in a given sample.
Seliwanoff’s test
Seliwanoff’s test is used to distinguish aldoses from ketoses. On treatment with conc. acid, ___ are dehydrated more rapidly to give furfural derivatives and on condensation with resorcinol give cherry red complex.
ketoses
Ketohexoses when treated with hydrochloric acid form ____
5-hydroxy methyl furfural
a cherry red colored precipitate within 5 minutes is obtained in Seliwanoff’s test indicate
presence of ketones
If the reaction is allowed for longer time, aldoses also produce positive results. A faint __ color is produced.
red
The formation of the cherry red-colored complex indicates a positive result which means that the given sample contains
ketones
The absence of such color or the appearance of the color after a prolonged period of time indicates a negative result which means that the test sample doesn’t have ____ .
Seliwanoff’s test
ketones
Seliwanoff’s test is positive for
Ketose Sugars
Ketose sugars include
Sucrose
Fructose
positive seliwanoff’s test looks like
cherry red solution
reagent of Seliwanoff’s test
Resorcinol
Hcl
chemical test used to differentiate reducing sugars from non-reducing sugars.
silver mirror test (Tollen’s reagent)
This test is also called the silver mirror test based on the end product of this test
Tollen’s test
To distinguish reducing sugars from non-reducing sugars.
To detect the presence of aldehyde containing carbohydrates and differentiate them from ketone containing carbohydrates.
what test
Tollen’s test
is routinely performed in chemical laboratories for the qualitative organic analysis, which distinguishes aldehydes from ketones.
Tollen’s test
is also used for the differentiation of reducing sugars from non-reducing sugars.
Tollen’s test
Tollen’s reagent is composed of
ammonia
silver nitrate
sodium hydroxide
On reacting with carbohydrate, elemental ___ is precipitating out of the solution, occasionally onto the inner surface of the reaction vessel. This produces silver mirror on the inner wall of the reaction vessel.
silver
The formation of a dark grey precipitate or silver mirror on the bottom and sides of the test tube indicates a positive result, which means that the given sample contains reducing ____
sugars/aldoses
The absence of such precipitate indicates a ___ result, which means that the test sample doesn’t have reducing sugars/ aldoses/ α-hydroxy ketoses.
negative
Study flowchart (in your gallery)
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Glucose result on the ff test:
Molisch
Fehling
Benedict
Tollen
Iodine
M - + (purple ring)
F - + (red precipitate)
B - + (red precipitate)
T - + (silver mirror)
I - - (no reaction)
Lactose result on the ff test:
Molisch
Fehling
Benedict
Tollen
Iodine
M - + (purple ring)
Fehling - + (red precipitate)
Benedict - + (red precipitate)
Tollen - + (silver mirror)
Iodine - - (no rx)
Sucrose result on the ff test:
Molisch
Fehling
Benedict
Tollen
Iodine
m +
f -
b -
t -
i -
starch result on the ff test:
Molisch
Fehling
Benedict
Tollen
Iodine
m - +
f - -
b - -
t - -
i - +
Based on the reactivity with Tollen’s, Benedict’s or Fehling’s reagent, carbohydrates are classified as;
Reducing
Non reducing
Sugar with free aldehyde or ketone group
All monosaccharides and most of the disaccharides
reducing sugars
can reduce Tollen’s, Benedict’s or Fehling’s reagents
reducing sugars
They do not get oxidized
Sucrose is their most common source
non reducing sugars
Cannot reduce Tollen’s, Benedict’s or Fehling’s reagents
non-reducing sugars
