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________ also known as saccharides, include a large group of ________ or _________ and their derivatives.
Carbohydrates, polyhdroxyaldehydes, polyhydroxyketones
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Carbohydrates are widely distributed in nature and make up most of the organic structures of all plants as well as being present to some extent in all animals. Their presence can be tested based on:
- A. the production of furfural and its derivatives
- B. their reducing property
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When a monosaccharide is treated with a strong mineral acid, _________________.
dehydration of the monosaccharide occurs
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The dehydrated product is ______ if the monosaccharide is a pentose and ___________ if the monosaccharide is a hexose.
furfural, hydroxymethylfurfural
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Give the illustration of the dehydrated product if the monosaccharide is a pentose and if the monosaccharide is a hexose.
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Various phenolic compounds like ________,_______ and _______ will condense with the furfural or hydroxymethyl furfural to form colored dyes.
a-naphtol, orcinol, resorcinol
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The formation of these colored condensation compounds is a ____________ for the presence of carbohydrates.
Positive test
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______ and _____ don't undergo this reaction since they don't posses the requisite minimum of five carbon atoms
Trioses and Tetroses
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What test which uses a-naphthol is the most general test for the presence of carbohydrates because it gives a positive test with all carbohydrates larger than teroses.
Molisch Test
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What test is useful in differentiating between hexoses and pentoses
Orcinol or Bial's Test
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Because orcinol condenses with furfural from pentoses to form a ___________ compound and with hydroxymethyl furfural from hexoses to form a _________ product.
- Pentoses: Blue-green
- Hexoses: Yellow-brown
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What test which uses resorcinol distinguishes aldohexoses from ketohexoses based on their differential rates of reaction with hot HCl.
Seliwanoff's Test
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_______ are dehydrated more rapidly than aldoses to give _____________ compounds which then condense with resorcinol (m-dihydroxybenzene) to form _________ complex.
Ketoses, hydroxymethyl furfural, cherry red
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Aldoses give a _______ that takes a longer time to develop. This test (Seliwanoff's Test) is most sensitive for __________ which is a ketose.
Light pink color, fructose
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A ______ is one which has a free hydroxyl group at the anomeric C.
Reducing sugar
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As the cyclic structure reverts to its open-chain form, the _______ is converted back to the _______.
free hydroxyl group, aldehyde
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The aldehyde group can be oxidized by reagents such as _________.
Benedict's reagent
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The oxidizing agent is Cu2+ that can be reduced to ____.
Cu+
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All sugars that react with Benedict's reagent are
reducing sugars
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All monosaccharides and some disaccharides have the ability to reduce an ___________.
alkaline solution of Cu2+ ion
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The Cu2+ ion which is less soluble precipitates out of the alkaline solution as a __________ precipitate of cuprous oxide.
Brick-red
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Give or illustrate the formation of the red cuprous oxide precipitate which is the criterion of a positive test.
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What test distinguishes between reducing monosaccharides and reducing disaccharides by a difference in rate of reaction.
Barfoed's Test
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Barfoed's reagent reacts with reducing monosaccharides, to produce cuprous oxide, faster than with reducing disaccharides. Give the equation or illustration.
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LAB ACTIVITY:
MATERIALS-
CHEMICALS-
(Study procedures in the book)
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What is the title of Activity No. 2?
QUALITATIVE ANALYSIS OF CARBOHYDRATES (I)
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