carbs powerpoint (lab) Flashcards
Molisch’s Test named after…?
Austrian botanist Hans Molisch
molischs test for the presence of _________________
carbohydrates
Reagents: A solution of naphthol in ethanol (95%)
* Sample: 2ml of 5% solution s of glucose, sucrose and starch
Molisch’s test
A positive
reaction is indicated by appearance of a PURPLE RING at the interface between the acid
and test layers.
Molisch’s test
Glycosidic bonds are hydrolyzed by conc. H2SO4, producing monosaccharides, dehydrated to furfural-forming substances — a
negative result is a good evidence of the absence of carbohydrates.
Molisch’s test
All carbohydrates – monosaccharides,
disaccharides, and polysaccharides – should
give a positive reaction
Molisch’s test
Reagent: NaOH (used to neutralize citric acid added for
hydrolysis)
* Sample: 1 ml of 5% glucose solution
1 ml of 5% sucrose solution
1 ml of 5% starch solution
Boiled and note the odor and color
Moore’s Test
Test is based on the liberation of aldehyde
A positive result will give a brown color with caramel like odor
Moore’s Test
- Sucrose negative result (no free aldehyde group), Colorless
- Glucose and Starch positive result
Moore’s Test
The Anthrone test is another general test for…?
carbohydrates
The H2SO4 hydrolyses
bound sugars to yield furfural or furfural derivatives. This reacts with __________ to form
colored compounds.
anthrone
Sample: 1 ml of 5% glucose solution, 1 ml of 5% sucrose solution, 1 ml of 5% starch
solution
Positive Result: Bluish green complex
All
anthrone test
The furfural or hydroxyfurfural formed condenses with two molecules of
napthol from anthrone reagent to form a ____-______ complex.
blue-green
Anthrone test and Molisch test are two types of _________ tests.
analytical
key difference between Anthrone and Molisch test
anthrone: detect carbs in blue-green
molisch: detect carbs in violet
formation of a crystalline dicarboxylic acid that is insoluble in dilute HNO3 (Nitric
Acid);
reaction unique for galactose and galactose compounds.
Mucic acid test
______ Acid – (colorless) catalyzes the hydrolysis of lactose to glucose and galactose, then oxidizes
both sugars to the _________________ acids (mucic acid crystals)
Nitric; tetrahydroxy
Specific test for galactose
Mucic acid test
Results: Galactose - white sandy precipitate
□ Lactose -white flakes precipitate
□ Glucose - Negative
Mucic acid test
(Theodor Seliwanoff)
Seliwanoff ’s Test
_______ is a chemical product resulting from the hydrolysis of pentoses
Furfural
Ketoses undergo dehydration to yield furfural derivatives more rapidly than aldoses, and form
complexes with resorcinol which are colored.
Seliwanoff ’s Test
Test to distinguish aldose (-) from ketose (+)
- Specific test for fructose
- Useful for detecting the presence of ketose
Seliwanoff ’s Test
Results:
- Sucrose and Fructose ⇛ Red/Cherry Red
- Lactose, Maltose, Glucose and Galactose ⇛ yellow
Seliwanoff ’s Test
Why should glucose and maltose give positive results upon
prolonged boiling with seliwanoff’s Reagents?
- The high concentration of glucose or other sugar may interfere by
producing similar colored compounds with seliwanoff’s reagent.
(Seliwanoff’s Test) Prolonged boiling can transform __________ to __________ by catalytic
action of acid and form cherry red complex giving a false- positive
result.
glucose to fructose
- A color reaction that is specific for pentoses.
BIAL’S TEST
(Bial’s test) It involves the decomposition
of these sugars when heated with conc. HCl (dehydrating agent) to
furfural, which condenses with orcinol (3,5- dihydroxytoluene) to form _________ to _________ colored compounds.
blue
to green
Sample: 5% ribose, glucose, fructose, galactose, maltose, lactose, sucrose
* Reagents: Orcinol, conc. HCl, Ferric chloride
* Result:
- Positive: Ribose (Pentose, 5 carbons)
Bial’s test
Detecting Dextrin from Starch
IODINE TEST
Iodine Test for Starch
deep blue
(Iodine test) Preparation of Dextrin from starch
violet
(Iodine test) Gum Arabic ( a non-digestible carbohydrate) with Iodine
No blue or red-brown color
(Iodine test) Agar-agar (starch) with Iodine –
dark brown color
- a galactose based heterogenous polysaccharide derived
from algae
Agar-agar (starch)
is a REDUCITON chemical test used to differentiate
between water-soluble aldehyde and ketone functional
groups,
Fehling’s Test
The REDUCTION test was developed by German chemist Hermann von
Fehling in 1849.
Fehling’s Test
Fehling’s A is a _____ _________
solution of copper(II) sulfate
blue aqueous
Fehling’s B is a _____ solution of aqueous potassium sodium
tartrate (also known as Rochelle salt) and a strong alkali
(commonly sodium hydroxide).
clear
Equal volumes of the two mixtures are mixed together to get
the final Fehling’s solution, which is a deep _______ color
blue
A positive result is indicated by the formation of a brick red
precipitate
fehling’s test
All sugar solutions produced a Brick red ppt except:
- Sucrose- Blue solution
fehling’s test
sugars that doesn’t have any free ketone or aldehyde groups
NON- REDUCING SUGARS
is sucrose a non-reducing sugar?
yes
like glucose and lactose, have
free ketone or aldehyde functional groups,
which enable the formation of a hemiacetal
reducing sugars
Benedict’s Test
test for the presence of
reducing sugars.
determines the presence of
non-reducing sugars in a test solution.
Benedict’s Test for non-reducing sugars
(benedict’s test)
- copper(II) sulphate/cupric sulfate
- sodium carbonate
- sodium citrate
The principal reagent in Benedict’s Test for Reducing Sugars
(benedict’s test) sugars which do not have an aldehyde or a
keto functional group - the reducing species
Non-reducing sugars
(benedict’s test) The absence of the aldehyde or keto group, cannot reduce ______ (__)
(blue) to the _______ (__) (red).
copper (II); copper(I)
(benedict’s test) Sucrose is the most common disaccharide ___-___________ sugar.
non-reducing
A Positive test produced a BRICK RED PRECIPITATE.
- (from blue to green to yellow to orange to brick red)
benedict’s test
used to test forthe presence of
glucose in urine.
benedict’s test
TRUE/FALSE? Only glucose is indicative of diabetes.
TRUE
presence of reducing sugars.
NYLANDER’S TEST
- Indicated by the formation of a dark brown to black precipitate
- all sugars are positive except for Sucrose
NYLANDER’S TEST
Yellow color; Reducing sugars will give a mahogany red color due to
the formation of sodium picramate
Picric acid test
detecting the
presence of monosaccharides from disaccharides.
Barfoed’s test
invented by Danish chemist ________ _________ Barfoed
and is primarily used in botany
CHRISTEN THOMSEN
Disaccharides may also react, but the reaction is much
slower.) thus they produced a negative results (blue solution)
Monosaccharides produced a brick red precipitate.
BARFOED
What product is formed when picric acid is reduced?
Sodium picramate
