Qualitative Analysis of Carbohydrates

Lim, Jean Rya Que
2013 – 72199

ATQ 1 – Qualitative Analysis of Carbohydrates

Data Sheet:

A. Osazone Formation

Crystals Formed? (hot)
Crystals Formed? (Cold)
5% sucrose
Yes (orange)
Yes (yellow)
5% glucose
Yes (orange)
Yes (yellow)
5% fructose
Yes (brown)
Yes (brown)
5% maltose
Yes (orange)
Yes (gold)

B. Molisch Test

Color of Junction
Glucose
Purple
Sucrose
Purple
Starch
Purple

C. Bial’s Test

Color Change
Ribose
Yellow -> Dirty Green
Glucose
Yellow -> Dark Yellow

D. Seliwanoff’s Test

Observation
Sucrose
1st (Dark)
Glucose
2nd (Medium)
Fructose
3rd (Light)

E. Benedict’s Test

Color Change
Glucose
light blue -> Orange
Fructose
light blue -> light olive green
Maltose
light blue -> yellow brown
Sucrose
light blue -> blue green
Starch
light blue -> no change
Distilled Water light blue -> no change

F. Barford’s Test

Observation
Amount of Precipitate
Glucose
Blue Solution, Red Precipitate
Most
Fructose

Less
Maltose

More
Sucrose

Least

G. Hydrolysis of Polysaccharides
Total Drops: 11 (11 mins. )
Color Changes: Dark Violet -> Brown -> Orange -> Yellow

Unhydrolyzed - > Hydrolyzed
Hydrolyzed Starch
Blue -> brown
Hydrolyzed Sucrose
Blue -> reddish brown

Questions:

1) Draw the structures of the osazones produced in the experiment.

2) Theoretically, arrange the following sugars according to their reactivity with the Benedict’s Reagent (Glucose, Fructose, Maltose, Sucrose, Starch)
Glucose > Fructose > Maltose > Sucrose > Starch

3) What is the difference between the Benedict’s Test and Barfoed’s Test? The Benedict’s Test is used to test for the presence of reducing sugars (ie. Monosaccharides, disacchararides etc.) Meanwhile, Barfoed’s Test only tests positive for monosaccharides making it a more specific test for sugars.

4) Can Seliwanoff’s Test be used to differentiate sucrose from fructose? Why? Seliwanoff’s Test cannot be used to differentiate sucrose from fructose because Sucrose contains both the