all carbohydrates test
TRANSCRIPT
All Carbohydrates Test
Iraq-Kurdistan-sulaymaniyah
Prepared:
Farhang Hamid
Gmail
Phone number
+9647701420962
INTRODUCTION Carbohydrates play many important roles in biological systems. They
represent the major form of chemical energy for both plants and animals.
In plants they represent the end product of photosynthesis, and therefore
connect all living systems to the sun’s sustaining light energy. Our
discussion of carbohydrates will also introduce us to biopolymers, of which
proteins and nucleic acids also belong. One of these polymers, the
structural polysaccharide cellulose, ties more of the earth’s organic carbon
than any other molecule.
Polymers are large molecules that are made by stringing together, like
beads on a string, smaller units called monomers.
Poly- is the Greek prefix meaning “many”.
The names of may polymers describe what they are made from
Polyethylene is made by stringing together many ethylene units.
Ethylene (ethane) is the monomer
Polypropylene is made by stringing together many propylene units.
Propylene (propene) is the monomer.
Polysaccharides are made by stringing together many monosaccharide’s.
Monosaccharide’s (simple sugars) are the monomers.
Carbohydrates as the name indicate are made from carbon (C) and hydrate
(H2O) and was originally applied to the compounds that gave the (CH2O)n
formula (Applicable for monosaccharaides and for example C6H12O6) and
often referred to as CHO.
Classification Carbohydrate 1- Monosaccharides:
2- Disaccharides:
3- Polysaccharides:
Test The Molisch-Test:-
Procedure: -
1- Add 1 ml Sample.
2- Add 2 Drop Molisch reagent. (10% α-naphthol in ethanol).
3- Add 1 ml H2SO4.
(Monosaccharide’s give a rapid positive test)
Principle:
Concentrated sulphuric acid hydrolyses glycosidic bonds to give the
monosaccharaides, which are then dehydrated to furfural and its
derivatives. These products then combine with sulphonated naphthol to
give a purple complex.
(Disaccharides and polysaccharides react slower but Monosaccharides give a rapid positive test.)
Solubility-Test:-
- Apply this test to all carbohydrates provided.
- Observe the solubility of the carbohydrates both in water and ethanol.
- DO NOT depend on your solubility observations during identification of
your unknown compound.
Barfoed's -Test:-
This test is used to distinguish between monosaccharide and
disaccharides. Barfoed's test is similar to Benedict’s test in using cupper
ions as an oxidising agent to form a carboxylic acid and a reddish
precipitate of cuprous oxide within three minutes. However, the test
medium is weakly acidic, therefore, only reducing monosaccharide’s give
positive result using Barfoed's reagent.
Preparing Reagent :
Barfoed's reagent consists of a 0.33 molar solution of neutral copper acetate in 1%
acetic acid solution. The reagent does not keep well and it is therefore advisable to
make it up when it is actually required.
Procedure: -
1- Add 0.5 ml of The Sample.
2- Add 1 ml of Barfoed reagent.
3- Boil 3-5 min in Water Bath.
Seliwanoff’s -Test:-
This test is used for identification of keto-hexoses or to distinguish
between ketoses and aldoses. Aldoses may react slightly and more slowly
to produce a faint pink color. Fructose and sucrose (A disaccharide
consisting of fructose and glucose) are two common sugars that give a
positive test.
Procedure: -
1- Add 2 Drop Sample to 2.5 ml Seliwanoff’s
Reagent. 0.5 g resorcinol per liter 10% HCl
2- Warm 1-2 min in Water Bath.
3-The red Color within 2 min indicates positive
Result Ketoses (Fructose , Sucrose).
two common sugars that give a
positive test
Ketoses (Fructose , Sucrose)
Bials -Test:-
Bial’s Test is to determine the presence of pentoses (5C sugars). The
components of this reagent are resorcinol, HCl, and ferric chloride. In this
test, the pentose is dehydrated to form furfural and the solution turns
bluish and a precipitate may form. Perform this test with ribose and
glucose.
Procedure:-
1- Add 0.5 ml Sample to 1.5 ml of Bials Reagent.
2- Heat Boiling in Water Bath.
3- The Formation of a Blue-Green Color positive Result for pentose.
compounds (pentosans) will give a positive test.
Benedict's -Test:-
:(also called Benedict's solution): is a chemical reagent named after an
American chemist, Stanley Rossiter Benedict . Benedict's reagent is used as
a test for the presence of reducing sugars. This includes all
monosaccharides and many disaccharides, including lactose and maltose.
Even more generally, Benedict's test will detect the presence of aldehydes
, and alpha-hydroxy-ketones, including those that occur in certain ketoses.
Thus, although the ketose fructose is not strictly a reducing sugar, it is an
alpha-hydroxy-ketone, and gives a positive test because it is converted to
the aldoses glucose and mannose by the base in the reagent.
The copper sulphate in Benedict's solution reacts with reducing sugars.
Benedict's solution can be used to tell if there is a sugar in a substance such
as glucose in starch .
Benedict's Reagent provides a quantitative test for reducing sugars along
with qualitative test. The color of the obtained precipitate gives an idea
about the quantity of sugar present in the solution. A greenish precipitate
indicates about 0.5% concentration; yellow precipitate indicates 1%
concentration; orange indicates 1.5% and red indicates 2% or higher
concentration. To test for the presence of monosaccharides and reducing
disaccharide sugars in food, the food sample is dissolved in water, and a
small amount of Benedict's reagent is added. During a water bath, which is
usually 4–10 minutes, the solution should progress in the colors of blue
(with no glucose present), green, yellow, orange, red, and then brick red or
brown (with high glucose present).A colour change would signify the
presence of glucose. The common disaccharides lactose and maltose are
directly detected by Benedict's reagent, because each contains a glucose
with a free reducing aldehyde moiety.
Sucrose (table sugar) contains two sugars (fructose and glucose) joined by
their glycosidic bond in such a way as to prevent the glucose isomerizing to
aldehyde, or the fructose to alpha hydroxy-ketone form. Sucrose is thus a
non-reducing sugar which does not react with Benedict's reagent. Sucrose
indirectly produces a positive result with Benedict's reagent if heated with
dilute hydrochloric acid prior to the test, although after this treatment it is
no longer sucrose. The acidic conditions and heat break the glycosidic bond
in sucrose through hydrolysis. The products of sucrose decomposition are
glucose and fructose, both of which can be detected by Benedict's reagent,
as described above.
Starches do not react or react very poorly with Benedict's reagent, due to
the relatively small number of reducing sugar moieties, which occur only at
the ends of carbohydrate chains. Benedict's reagent can be used to test for
the presence of glucose in urine. Glucose found to be present in urine is an
indication of diabetes mellitus. Once a reducing sugar is detected in urine,
further tests have to be undergone in order to ascertain which sugar is
present. Only glucose is indicative of diabetes.
What is a reducing sugar?
Sugars are classified as reducing or non-reducing based on their ability to
act as a reducing agent during the Benedict's Test. A reducing agent
donates electrons during a redox reaction and is itself oxidized.
The aldehyde functional group is the reducing agent in reducing sugars.
Reducing sugars have either an aldehyde functional group or have a ketone
group - in an open chain form - which can be converted into an aldehyde.
Reducing sugars are simple sugars and include all monosaccharides and
most disaccarides. Some examples of monosaccharides are glucose,
fructose and galactose.Examples of reducing disaccharides are lactose and
maltose.
Procedure:-
1- Add 2 ml Sample in Test Tube.
2- Add 1 ml Benedict’s Reagent.
3- Boil 10-15 min in Water Bath.
Starch - Iodine -Test:-
Starch:
Plants store glucose as the polysaccharide starch. The cereal grains
(wheat, rice, corn, oats, barley) as well as tubers such as potatoes are rich
in starch.
Starch can be separated into two fractions--amylose and amylopectin.
Natural starches are mixtures of amylose (10-20%) and amylopectin (80-
90%).
Amylose forms a colloidal dispersion in hot water whereas amylopectin is
completely insoluble. The structure of amylose consists of long polymer
chains of glucose units connected by an alpha acetal linkage.
Chemical Test for Starch or Iodine:
Amylose in starch is responsible for the formation of a deep blue
color in the presence of iodine. The iodine molecule slips inside of the
amylose coil.
Iodine - KI Reagent: Iodine is not very soluble in water, therefore the
iodine reagent is made by dissolving iodine in water in the presence of
potassium iodide.
Starch Test: Add Iodine-KI reagent to a solution or directly on a potato or
other materials such as bread, crackers, or flour. A blue-black color results
if starch is present. If starch amylose is not present, then the color will
stay orange or yellow. Starch amylopectin does not give the color, nor
does cellulose, nor do disaccharides such as sucrose in sugar.
Iodine Test: When following the changes in some inorganic oxidation
reduction reactions, iodine may be used as an indicator to follow the
changes of iodide ion and iodine element. Soluble starch solution is
added. Only iodine element in the presence of iodide ion will give the
characteristic blue black color. Neither iodine element alone nor iodide
ions alone will give the color result.
Procedure:-
1- Add 2 ml Sample in Test Tube. (1 ml)
2- Add 2 ml Iodin. (1 ml)
Prepared:
Farhang Hamid
Gmail
Phone number
+9647701420962