TEST FOR CARBOHYDRATES

Question 1

It is a general test for carbohydrates.

Compounds that are dehydrated by concentrated H2SO4, to form furfural or hydroxy methylfurfural will react with alpha napthol (in the Molisch’s reagent) to yield a purple condensation product.

Although not a specific test for carbohydrates, a negative result is good evidence of the absence of carbohydrates.
Used as a general test for
carbohydrates, forming a purple ring at the interface, indicating the presence of carbohydrates through furfural formation.

Answer 1

Molisch’s Test

Question 2

It is a specific test for reducing sugars or the presence of free or potential aldehydes.

A positive test is the appearance of a red-orange precipitate Cu2O.
However, the size of the particles may make it too orange or yellow or green if there is much deep blue cupric ion unreacted.

detected reducing sugars by producing a red-orange precipitate, with the color intensity varying depending on the sugar concentration.

Answer 2

Benedict’s Test

Question 3

It is a test used to distinguish between monosaccharides and disaccharides.

A positive reaction may be only a little dark red precipitate in the bottom of the test tube.

If this appears within 2-3 minutes, it indicates a monosaccharide, if it does not appear or show after 10 minutes, disaccharide is indicated.

Answer 3

Barfoed’s Test

Question 4

It is a specific test for ketoses.

> The dehydration of ketohexoses with hot HCl occurs much faster than the dehydration of the corresponding aldohexoses.

> During the same time interval in which the dehydrated ketohexose reacts with the resorcinol (in the Seliwanoffs reagent) to form a bright red condensation product, the aldohexose yields only a pale pink coloration.
This test is useful for distinguishing
fructose (ketohexose) from glucose, mannose and galactose.

Answer 4

Seliwanoff’s Test

Question 5

It is a test for pentoses and nucleotides that contain the pentose sugar.
> It is based on the observation that furfural which is formed from a pentoses yields a blue-green compound when treated with orcinol in the presence of ferric ions (in the Bial’s reagent).

> It is not specific for pentoses since other compounds such as trioses, uronic acids and certain heptoses, will produce blue or green products.

> Hydroxymethy|furfural (formed
from hexoses) will give a yellow-brown condensation product.

> confirmed the presence of pentoses by producing a blue-green compound, a reaction indicative of furfural formation from pentoses.

Answer 5

Bial’s Test

Question 6

gives a blue-black color
(Amylose) with iodine.

> formed a blue color when starch was present, indicating the complex interaction between iodine and polysaccharides.

Answer 6

Iodine test for starch

Question 7

In molisch’s test, what sample is negative?

Answer 7

distilled water

Question 8

In benedict’s test, what samples are negative?

Answer 8

Starch
Distilled water
Sucrose

Question 9

in barfoed’s test, which of the ff showed no ppt?

Answer 9

Starch
Sucrose
Lactose
Distilled water

Question 10

In bial’s test, which of the following sample is positive?

Answer 10

ribose

Question 11

in seliwanoff’s test, which of the ff samples is positive?

Answer 11

Sucrose and Fructose

Question 12

What are the products formed when sucrose is hydrolyzed?

Answer 12

Glucose + Fructose

Question 13

What are the products formed when lactose is hydrolyzed?

Answer 13

D-Galactose + D-Glucose

Question 14

What are the products formed when maltose is hydrolyzed?

Answer 14

Glucose + Glucose

Question 15

What are the products formed when starch is hydrolyzed?

Answer 15

Glucose + Maltose

Question 16

What prevents human from digesting cellulose?

Answer 16

Humans can’t digest cellulose because we lack the enzyme CELLULASE needed to break it down.

Question 17

Explain the difference between the metabolism of fructose and of glucose in the human body.

Answer 17

Fructose is metabolized in the liver, where it promotes fat production, occurs at a much faster rate, and is less strictly regulated than glucose.The conversion of dietary fructose to energy is known as fructolysis.

In contrast, glucose is used by the body’s cells as an energy source; it is processed in the intestines and transported through the blood via a process
called glycolysis.

Question 18

Which carbohydrate test is appropriate to detect the presence of sugar in urine?
Explain why.

Answer 18

• The Benedict’s test is appropriate for detecting the presence of sugar in urine.
• This test identifies reducing sugars, such as glucose, by producing a color change when the urine sample is heated with Benedict’s reagent, resulting in a brick-red precipitate, if glucose is present.
• It is widely used because it is simple, quick, and effective for diagnosing conditions like diabetes
mellitus.

Question 19

Photosynthesis Formula

Answer 19

6CO2 + 6H2 O -> C6 H12 O6 + 6O2

Question 20

in act 7 benedict’s test, what fruit is positive?

Answer 20

watermelon

Question 21

what is the composition of Molisch’s test?

Answer 21

a-napthol

Question 22

what is the indication of positive in molisch’s test?

Answer 22

Purple/Red

Question 23

What is the composition of Benedict’s test?

Answer 23

Naoh+CuSO4

Question 24

Indication of positive result in Benedict’s test?

Answer 24

Brick red ppt or RED ORANGE PRECIPITATE

Question 25

What is the composition of Barfoed’s test?

Answer 25

Cupric acetate + acetic acid

Question 26

Indication of positive result in Barfoed’s test:

Answer 26

Brick red or LITTLE DARK RED PPT

Question 27

What is the composition of Seliwanoff’s test?

Answer 27

resorcinol

Question 28

Indication of positive result in Seliwanoff’s test:

Answer 28

Red
ketohexose- bright red condensation
aldohexsose- pale pink coloration

Question 29

What is the composition of Bial’s test?

Answer 29

Resorcinol + Fe

Question 30

Indication of positive result in Bial’s test

Answer 30

BLUE GREEN

Question 31

is a carbohydrate that reacts with a mild oxidizing agent to form an aldonic acid.

Answer 31

Reducing sugar

Question 32

is a carbohydrate that reacts with a mild oxidizing agent to form an aldonic acid.

Answer 32

Reducing sugar

Question 33

donates electrons during a redox reaction and is itself oxidized.

Answer 33

reducing agent

Question 34

common oxidizing agents used to test for the presence of reducing sugar is.

Answer 34

Benedict’s solution

Question 35

in benedicts test it is clear, light blue, which concludes to the classification of non reducing sugar

Answer 35

SUCROSE

Question 36

presence of the alkaline sodium carbonate converts the sugar into a strong reducing agent called

Answer 36

enediols

Question 37

During the reaction, enediols decrease the cupric particles (Cuz+) present in Benedict’s reagent to ____________ which appear as red
copper oxide that is insoluble in water

Answer 37

cuprous particles

Question 38

is a sweetener derived from corn syrup, which is processed from corn. it is a common sweetener in sodas and fruit-flavored drinks. As use has increased, so have levels of obesity and related health problems. Some wonder if there’s a connection.

Answer 38

High fructose corn syrup (HFCS)