Post lab questions (Lab Report Sample)

Chemistry 1120 Laboratory-Experiment #7-carbohydrates
Theoretical questions
1 State 3 classes of carbohydrates and give examples of each
* Monosaccharides: glucose and fructose
* Disaccharides: Sucrose and lactose
* Polysaccharides: starch
2 For monosaccharides:
* Distinguish between aldose and ketose
An aldose is a monosaccharide with an aldehyde group while a ketose is a monosaccharide with a ketone group.
* Give the term used for a carbon chain length of three, four, five, and six carbons
* Three: tri
* Four: tetra
* Five: pent
* Six: hex
* Draw a structure of ketohexose
3 Define what it means for carbohydrates to be a reducing sugar. Are all carbohydrates reducing sugars? Draw a Haworth structure for any monosaccharide and explain how you would tell it is a reducing sugar.
Any carbohydrate that is capable of causing the reduction of some other substances without being hydrolyzed first is the reducing sugar. Not all carbohydrates are reducing sugars.
Haworth structure of alpha glucose.
it has an open-chain form with an aldehyde group, hence a reducing sugar.
Conclusion questions
1 In Benedict’s test, did you get the expected results for each carbohydrate? How do you know?
No, we expect disaccharides to be non-reducing sugars but lactose was found to be reducing just as monosaccharides.
2 In Barfoed’s test, did you get the expected results for each carbohydrate? How do you know?
Yes, only glucose and fructose were positive. The rest were negative since they do not have monosaccharides.
3 In testing each carbohydrate with Seliwanoff’s reagent, did you get the expected results for each carbohydrate? How do you know?
Yes, all of them were positive showing the presence of an aldehyde.
4 In testing each carbohydrate with iodine solution, did you get the expected results for each carbohydrate? How do you know?
Yes, only starch was positive and the rest were negative showing they did not contain starch.
Carbohydrate
Observation
1
* Which carbohydrate tested acted as a reducing agent?
* Glucose
* Fructose
* Lactose
* Which carbohydrates were not reducing?
* Starch
* Sucrose
2
* Which carbohydrate tested acted as a reducing agent?
* Glucose
* Fructose
* Which carbohydrates were not reducing?
* Lactose
* Sucrose
* starch
3
* Which carbohydrate revealed ketohexoses?
* Glucose
* Fructose
* Lactose
* Sucrose
* starch
* Which carbohydrate did not reveal ketohexoses?
None
4
* What color did colloidal starch turn upon the addition of iodine solution?
Dark purple
* Did sugars give a + or – reaction with iodine?
All sugars gave – reaction with iodine except starch which gave a positive reaction with iodine.
5
* What was the color change when I2 was placed on the cracker?
Dark purple
* Name some other food suitable for this starch test.
* potatoes
* rice
* bread
* Give the name of several foods which contain cellulose
* Rice
* Corn
* Wheat straw
6
* Give the color change
* Apple juice: dark orange
* Raisins: light orange
* Saltline crackers: green
* From the c