Pre-Test Carbohydrates EXP 6 Flashcards
what is carbohydrates molecular formula?
Cn(H20)n
what are monosaccharides?
simple carbohydrates
what are aldoses?
monosaccharide that is polyhydroxy aldehydes with a general structure of A is also known as aldoses
what are ketoses?
monosaccharide that is polyhydroxy ketones with a general structure of B is also known as ketoses
examples of monosaccharides give 3
glucose, fructose, ribose
examples of disaccharides give 3
maltose, sucrose, lactose
how many carbons does monosaccharides consist of?
3-6 carbons
if there are 3-6 carbons in monosaccharide, how do you classify each one of them?
3C = trioses 4C = tetroses
5C = pentoses 6C = hexoses
what are disaccharides?
when two monosaccharides combine with the loss of one molecule water is when disaccharides are formed
what is a glycosidic bond?
its the bond that connects 2 monosaccharide unit in a disaccharide
in a figure chart, how do you differentiate ribose, glucose and fructose?
ribose has only 3 chain of (hydroxide, carbon and hydrogen) while glucose has 4 chain of (hydroxide, carbon and hydrogen) and fructose has a double bond Carbon and Oxygen with only 3 chains of (hydroxide, carbon and hydrogen)
what is a polysaccharide?
many monosaccharides linked together
examples of polysaccharides give 4
starch, pectin, glycogen and cellulose
what general test is for the presence of carbohydrates?
Molisch Test
how does the Molisch test work? explain in details
Molisch test is involved adding the Molisch’s reagent to the analyte and an addition of a few drops of concentrated sulfuric acid which (H2SO4) to the mixture. The formation of purple or purplish-red ring confirms the presence of carbohydrates in the analyte.
who was credited with the discovery of the Molisch’s test?
Czech-Austrian botanist Han Molisch
TRUE OR FALSE: EXPLAIN
A positive reaction for Molisch’s test is given by almost all carbohydrates
FALSE because there are exceptions like tetroses and trioses which are monosaccharides that only have 4 carbons and 3 carbons and generally would not produce a positive reaction
what is a reducing sugar?
it is a carbohydrate that is oxidized by a weak oxidizing agent in basic aqueous solutions
what is a non-reducing sugar
it is a carbohydrate that has not been oxidized
TRUE OR FALSE: EXPLAIN
all aldoses are the true reducing sugars because they contain the aldehyde functional group
TRUE since aldoses contain the aldehyde functional group they are all reducing sugars
TRUE OR FALSE: EXPLAIN
ketoses contain ketones and not aldehydes however they also still show reducing sugar properties
TRUE because in basic aqueous solutions ketoses undergo a process called keto-enol tautomerization that converts ketoses into a mixture of aldoses thus we can say that monosaccharides are all reducing sugars
TRUE OR FALSE: EXPLAIN
Disaccharides are all reducing sugars
FALSE because disaccharides may be reducing sugars or not. Only disaccharides that are reducing are those that contain free anomeric carbon because the free anomeric carbon has the capacity to open and expose the aldehyde group
TRUE OR FALSE: EXPLAIN
All polysaccharides are reducing
FALSE polysaccharides are non-reducing sugars typically because it consists of many monosaccharides linked up together
How do you test a carbohydrate if it is reducing or not? Explain in details.
There are many weak oxidizing agents to test if a carbohydrate is reducing or not such as the Benedict’s reagent, Fehling’s reagent, Tollen’s reagent, Nylander’s reagent, and picric acid with sodium carbonate solution.
knowing all of the weak oxidizing agents to determine whether the carbohydrate is either a reducing sugar or not, what do they all have in common?
they are all in basic conditions which means their pH levels are always greater than 7
what is a picric acid test?
is a test when a saturated picric acid solution is used as an oxidizing agent. the environment is made alkaline by 10% Na2CO3. A formation of mahogany red colored solution which is due to the reduction of picric acid to picramic acid indicates a positive result
what is the benedict’s test?
it is a test based on cupric ion (Cu2+) that will oxidize aliphatic aldehydes such as aldoses including a-hydroxyaldehydes. A formation of a brick red precipitate of cuprous oxide (Cu2O) indicates a positive test. However, the color of the precipitate can vary from red to orange to green depending on the amount of sugar present in the solution. Hence, why the benedict’s test can be used to quantitatively estimate the amount of sugar in a solution. Benedict’s test can also be used to detect glucose in the urine for example.
What is Moore’s Test
reducing sugars have free carbonyl groups in their structure. At basic environment, this carbonyl group can undergo aldol condensation. For reducing sugars, the product is caramel with a brown color and characteristic odor. The odor intensifies when carefully acidified with diluted sulfuric acid.
What is Seliwanoff’s Test for Ketoses?
Seliwanoff’s test is used to distinguish aldoses from ketoses. Seliwanoff’s reagent dehydrates ketoses more rapidly and the derivatives undergo condensation reaction with resorcinol that gives a cherry red solution after 2 minutes which indicates a positive test. Seliwanoff’s test can be keto-containing carbohydrates
What is Iodine Test for Polysaccharides?
Iodine test is a very specific test for polysaccharides because polysaccharides have highly coiled structures. The color depends on the length of the linear chain available for complex formation. Therefore, different colors are produced for different polysaccharides.
What is Bial’s Test for Pentoses?
Bial’s test is used to distinguish pentoses from hexoses. The distinction is based on the color that develops in the presence of the reagent. If a pentose is present it will produce bluish-green solution. If a hexose is present it will produce a
muddy-brown, yellow or gray solution.
what is barfoed’s test for monosaccharides?
Barfoed’s test depends on the reducing properties of sugars. The oxidizing reagent used here is like benedict’s test which is cupric ion (Cu2+). A positive test for monosaccharides is indicated by the formation of the brick red precipitate of Cu2O within 2-3 minutes.
