Experiment 6: Qualitative Analysis of Carbohydrates

Question 1

Carbohydrates

Answer 1

Hydrate of carbon
Empirical Formula: CnH2nOn or Cn(H2O)n

Question 2

Disaccharide

Answer 2

Two monosaccharide units connected by glycosidic bond

Question 3

Polysaccharide

Answer 3

Hundreds-thousands of monosaccharide units connected by glycosidic bond

Question 4

Molisch Test Purpose

Answer 4

Test ALL carbohydrates

Question 5

Molisch Test Reagent

Answer 5

alpha-naphthol with sulfuric acid

Question 6

Molisch Test Positive and Negative Result

Answer 6

Positive: Purple ring at the interface
Negative: Colorless

Question 7

Molisch Test Reaction

Answer 7

(1) Dehydration of carbohydrate to alkene
(2) Formation alpha-naphthol complex

Question 8

Molisch Test Procedure

Answer 8

1. +5 drops of Molisch reagent in each test tube
2. TIlt test tubes
3. +15 drops of concentrated sulfuric acid to flow down
4. Note observations

Question 9

Iodine Test Purpose

Answer 9

Find starch and glycogen (storage)

Question 10

Iodine Test Reagent

Answer 10

Iodine Solution

Question 11

Iodine Test Positive and Negative Result

Answer 11

Positive: Dark blue mixture
Negative: Yellow (iodine solution)

Question 12

Iodine Test Reaction

Answer 12

Formation of Iodine complex
-I2 in KI+I—->I3- (surrounded by starch)

Question 13

Iodine Test Procedure

Answer 13

1. +5 drops of iodine solution into each test tube
2. Note observations

Question 14

Benedict Test Purpose

Answer 14

Detect reducing sugars (have free anomeric carbon

Question 15

Benedict Test Reagent

Answer 15

Copper (II) sulfate in citrate and carbonate (basic)

Question 16

Benedict Test Positive and Negative Result

Answer 16

Positive: Red-orange solution
Negative: Green blue solution (copper color)

Question 17

Benedict Test Reaction

Answer 17

Oxidation of free aldehyde or ketone group (results in ring opening) and formation of brick-red precipitate (Cu2O)

Question 18

Benedict Test Procedure

Answer 18

1. +25 drops of Benedict’s reagent into each test tube
2. Heat test tubes in boiling water for 2 minutes.
3. Remove and note observations

Question 19

Barfoed’s Test Purpose

Answer 19

Differentiate monosaccharide to disaccharide

Question 20

Barfoed’s Test Reagent

Answer 20

Copper (II) acetate in glacial acetic acid (acidic environment)

Question 21

Barfoed’s Test Positive and Negative Result

Answer 21

Monosaccharide: Fast formation of red precipitate
Disaccharide: Slow formation of red precipitation (Needs to break the glycosidic bond and to reveal anomeric carbon)

Question 22

Barfoed’s Test Reaction

Answer 22

Oxidation of free aldehyde or ketone group (ring opening) and formation of brick-red precipitate (Cu2O)

Question 23

Barfoed’s Test Procedure

Answer 23

1. +25 drops of Barfoed’s reagent
2. Heat for 5 minutes
3. Record time (fast formation of precipitate is monosaccharide, slow is disaccharide)

Question 24

Seliwanoff’s Test Purpose

Answer 24

Detect ketose

Question 25

Seliwanoff's Test Reagent

Answer 25

Resorcinol in concentrated HCl

Question 26

Seliwanoff's Test Positive and Negative Result

Answer 26

Positive: Cherry Red solution (or slightly pink) Negative: No significant color changes (color based on HCl color)

Question 27

Seliwanoff's Test Reaction

Answer 27

(1) Dehydration of ketohexose to 5-hydroxymethylfurfural (2) Complexation of resorcinol to 5-hydromethylfurfural (creates the red color)

Question 28

Seliwanoff's Test Procedure

Answer 28

1. +25 drops of Seliwanoff's reagent into each test tube 2. Heat test tubes in boiling water bath 3. Take note of color changes and time it takes for it to form

Question 29

Bial's Test Purpose

Answer 29

Find pentose

Question 30

Bial's Test Reagent

Answer 30

Orcinol, ferric (III) chloride (catalyst), concentrated HCl

Question 31

Bial's Test Reaction

Answer 31

(1) Dehydration of pentose to furfural (2) Formation of orcinol complex

Question 32

Bial's Test Positive and Negative Result

Answer 32

Positive: Blue green solution (FeCl3) Negative: Yellow (Concentrated HCl color)

Question 33

Bial's Test Procedure

Answer 33

1. +25 drops of Bial's Orcinol reagent 2. Heat test tubes in boiling water and note observations

Question 34

Samples that got positive results in Molisch Test

Answer 34

All of them

Question 35

Samples that got positive results in Iodine test

Answer 35

Amylose

Question 36

Samples that got positive results in Benedict Test

Answer 36

Xylose, glucose, galactose, fructose, maltose, lactose

Question 37

Samples that got positive results in Barfoed's Test

Answer 37

Xylose, glucose, galactose, fructose, maltose (slow), lactose (slow)

Question 38

Samples that got positive results in Seliwanoff Test

Answer 38

Fructose amd sucrose

Question 39

Samples that got positive results in Bial's Test

Answer 39

Xylose

Question 40

Xylose structure

Answer 40

-Aldopentose (5 carbons and aldehyde) -Monosaccharide *Glucose OH order (bad finger) but only has 5 carbons

Question 41

Glucose structure

Answer 41

-Aldohexose (6 carbons and aldehyde) -Monosaccharide *Bad finger -OH formation

Question 42

Galactose structure

Answer 42

-Aldohexose (6 carbons and aldehyde) -Monosaccharide *C3 and C4 OH direction at left

Question 43

Fructose structure

Answer 43

-Ketohexose (6 carbons and ketone) -Monosaccharide *Glucose (bad finger) but ketone

Question 44

Maltose structure

Answer 44

alpha Glc(1-->4)Glc linkage

Question 45

Lactose strcuture

Answer 45

Beta Gal(1-->4)Glc linkage

Question 46

Sucrose structure

Answer 46

Alpha Glc(1-->2)beta Fru linkage