a, Principle: The Trommer reaction is used to test for the presence of reducing sugars, 2+ based on their ability ability to reduce metals metals (in this case case Cu ). With heating in the boiling water bath, Cu(OH)2 (the light-blue solution) is reduced to Cu 2O (red precipitate).
2 Cu(OH)2 + Reducing sugar
Heat
Cu2O + 2H2O + Oxidized Sugar
b, Procedures:
1. Label 3 test tubes as 1 to 3 2. Add test solution (sugar) to each tube as follows: Tube 1: 1 mL of 1% Sucrose Tube 2: 1mL of 1% Glucose Tube 3: 1m: of 1% 1 % Maltose 3. Add 1 mL of 10% NaOH to each tube 4. Add 5 drops of 5% CuSO4 to each tube 5. Put the test tubes in the boiling water bath 6. Observe the changes of color. c, Explaination and result:
Tube 1: Do not have the precipitation: Explain: Sucrose is a disaccaride, so there is no have hemi-acetal group. There fore, it can’t reduce Cu(OH) 2 (light-blue solution) to Cu2O (brick-red precipitate).
2+
-
+ Cu + OH Tube 2: Have brick-red color precipitate:
Explain: Glucose is a monosaccaride, so there are the hemi-acetal groups. Thus, it can reduce Cu(OH)2 to Cu2O.
Tube 3: Also have the brick-red color precipitate, but the color in here is lighter than in tube 2. Explain: Although Maltose is a disaccaride, it also has the hemi-acetal groups. So, it can reduce Cu(OH)2 to Cu2O.
d, Conclusion: Sucarose is not a reducing sugar. Glucose and Maltose are reducing sugars, and the reduced ability of Glucose is stronger than Maltose. II.
Experiment 2: Quantitative determination of reducing sugars by Ixekutz:
a. Principle:
Reducing sugar + K 3Fe(CN)6
o
t
oxidize productions + K 4Fe(CN)6
K 4Fe(CN)6 + ZnSO4 K 3Fe(CN)6 + KI
precipitated complex CH3COOH
I2
+
K 4Fe(CN)6
Na2S2O3
+ I2
Starch
Na2S4O6
+
NaI
b. Procedures:
Step 1: Prepare sugar extraction: 1. Weigh 5 gram sample and add distilled water 2. Transfer the solution into volumetric flask 100 mL 3. Volume up with distilled water Step 2: Titration: 1. Take 2 triangle flasks and label as experiment flask (TN) and control flask (DC). 2. DC flask: add 10 mL of distilled water TN flask: add 5mL of sugar extraction plus 5 mL of distilled water 3. Add 10mL of 0,05N K 3Fe(CN)6 to each flask. 4. Add 10mL mixture of KI and ZnSO4 to each flask. 5. Add 10mL CH3COOH to each flask. 6. Add 3 drops of starch to each flask. 7. Titrate by Na2S2O3 until the milk-white color appear. c. Calculations:
The volume of Na2S2O3 used for DC flask: 8.5 mL
() The volume of Na2S2O3 used for TN flask: 4,5 mL
So:
The amount of 0,05N K 3Fe(CN)6 reacted with reducing sugar: 10mL – 5.29mL = 4.71 mL We can calculate amount of reducing sugars in solution (according table 2).
0,05N K 3Fe(CN)6
d.
Reducing sugar
mL
mg
4.7
7.55
0.01
0.015
4.71
7.565
Conclusion:
The weight of reducing sugar in the sample is: 7.565 x 20 = 151.3 mg Because we just use 1/20 of the sugar extraction solution to titrate. The percentage of reducing sugar is:
With: a (mg) is the weight of the reducing sugar.
A (g) is the weight of the sample. III.
Experiment 3: Quantitive determination of total sugar:
a. Procedures:
Step 1: Prepare sugarhydrolysis solution: 1. Prepare 1 triangle flask. 2. Add 10mL sugar extraction solution (prepared in exp.2 to step 1) to triangle flask. 3. Add 2 mL of 6N HCl to triangle flask. 4. Put the flask into the water boiling bath in 20 minutes. 5. Add 3 drops of phenolphtalein. 6. Add NaOH until the solution change to pik color. 7. Add 4 drops of CH3COOH until the solution change to colorless 8. Volume up to the volumetric flask 50mL.
Step 2: Titration: 1. Prepare 1 triangle flask. 2. Add 5 mL of sugar hydrolysis solution + 5 mL of distilled water 3. Titrate by Na2S2O3 like step 2 of exp 2. b. Calculations:
The volume of Na2S2O3 used: 8.3 mL Based on the given table we have: Na2S2O3
reducing sugar
mL
mg
8.30
13.8
Because after hydrolysis all the sugar changed to reducing sugar. There fore, the amount of reducing sugar after the react is equal with the amount of total sugar. c. Conclution: The weight of reducing sugar in the sample is: 13.8 x 10 x 2 = 276 mg Because we just use 1/10 of the sugar extraction solution to use to hydrolyze & 1/2 of the sugar hydrolysis solution to titrate. The percentage of total sugar in the sample is:
