Name:______________________________________________
Date:________________ P.______
CARBOHYDRATE PRE-LAB
Carbohydrates are organic molecules that come in all shapes and sizes. Plant and animals rely on
carbohydrates as their main source of energy. The simplest carbohydrates, such as glucose, form a single
carbon ring while other, more complex carbohydrates like starch, may consist of hundreds of carbon
rings held together by chemical bonds. There are three different groups of carbohydrates and are
categorized by how many carbon rings they are made up of: monosaccharides, disaccharides, and
polysaccharides. NOTE: We commonly call carbohydrates sugar because “saccharide” means sugar.
GROUP 1 – “Monosaccharide”
The simplest carbohydrate is called a monosaccharide. The prefix mono- means one. Monosaccharides
consist of a single carbon ring (see below). However, these molecules can have different shapes due to
different arrangements of atoms. When molecules have the same chemical formula but different shapes
we call them isomers of one other. Three common examples of monosaccharrides are: glucose, fructose,
and galactose.
Examine the structural formulas of these three sugars below and answer questions 1-6.
1. What three chemical elements are present in the three monosaccharrides shown? NOTE: The letter “C”
is for carbon. ________________________, _________________________, ________________________
2. Add the subscripts for each molecule below
a. glucose = C H O
b. fructose = C H
O
c. galactose = C H
O
3. What do you notice about all three simple formulas? __________________________________________________________
4. Are there twice as many hydrogen atoms as oxygen? ____________
5. Compare the structural formula for glucose and fructose.
a. are they exactly the same shape? ____________
b. are they both monosaccharrides? ___________
c. molecules that have the same chemical formula but have different shapes are called ______________
GROUP 2 – “The Disaccharides”
Two monosaccharide sugar molecules can join chemically to form a bigger carbohydrate molecule called
a double sugar, or disaccharide. The prefix di- means two. Disaccharides have two carbon rings. For
example, joining a glucose molecule with a fructose molecule (two monosaccharrides) produces a
disaccharide called sucrose. You may be familiar with sucrose especially if you put it on your Cheerios in
the morning!!!
Use the paper models to complete the questions below:
6. Cut out a model of glucose and a model of fructose and attempt to join and make sucrose. Do the
glucose and fructose molecule fit easily?_____________________
7. In order to join the two molecules, remove an –OH end from one molecule and an –H end form the
other. Cut along dotted lines. Do they easily join now?________________
8. The -H and –OH ends that were removed can also fit together. This new molecule has a chemical
formula of _________________ and is called _____________________.
NOTE: A chemical reaction that bonds two molecules together and in the process forms water is
called a condensation reaction.
9. Write the simple formula for sucrose by adding the chemical formulas for glucose and fructose and
then subtracting the chemical formula for water. Sucrose chemical formula = ________________________.
10. What common name do we give sucrose?____________________________________
11. Different disaccharide molecules can be made by joining other monosaccharrides in different
combinations. For example, by joining glucose with another glucose, a double sugar called maltose is
formed. Cut out two models of glucose. What must be removed in order to make them fit? _________________
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12. Write the chemical formula for maltose. (Glucose + Glucose) – water = _____________________. Double
check your answer by counting each atom in maltose using the diagram above.
13. How do the simple formulas for maltose and sucrose compare? ____________________________________________
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14. Are there twice as many hydrogen atoms as there are oxygen atoms in a disaccharide?____________
15. How many monosaccharide molecules are needed to form sucrose?________. What about maltose?______
GROUP 3 – “The Polysaccharides”
Just as double sugars were formed from two single sugar molecules, polysaccharides are formed when
many single sugars are chemically joined. The prefix poly- means many. Starch, glycogen, and cellulose
are the three most common polysaccharides in biology. They consist of very, very long chains of glucose
molecules.
16. Take your maltose molecule (two glucoses) and add a third molecule of glucose. Turn to a lab group
near by and join polysaccharides. Find another group near by and join molecules. Do this until we have
constructed an entire class polysaccharide. This is only a fraction of an actual polysaccharide. For
example, a typical starch molecule consists of hundreds of glucose molecules.
17. What must be removed in order to join these molecules together?________________
18. The chemical formula for a polysaccharide may be written as (C6H10O5)n. The n equals the number of
times the monosaccharide is repeated.
a. If a starch molecule had 100 repeats, what would its chemical formula look like? (C6H10O5)_____
b. How many of each element would be present (write as subscripts) C
H
O
19. This activity models the formation of a linear polysaccharide consisting of 20 or so glucose molecules.
In actuality, polysaccharides may contain hundreds of monosaccharides and they may come in many
shapes from helical to those that branch out. In all cases, polysaccharides are made of many
______________________________________ chemically ___________________ together.
20. Summarize what you have learned from doing this activity? _______________________________________________
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MATERIALS: test tubes, markers and tape for labeling, Benedict’s solution, iodine solution, droppers, hot
plates, water, glass beakers, monosaccharide solution, disaccharide solution, polysaccharide solution, 5
unknown carbohydrate solutions.
SAFETY: Benedict’s solution is a hazardous eye irritant and harmful if swallowed, Iodine solution may be
absorbed through skin and is toxic f swallowed, hot plates and boiling water, working with glassware.
PROCEDURES:
A. Benedict’s Test - Monosaccharide
1.) Fill a 500mL beaker half full of water. Bring to boil.
2.) Number three clean test tubes: “1-mono”, “2-di”, and “3-poly”
3.) Using a clean dropper for each tube, place 30 drops of the following:
a. Tube 1 = 30 drops of known monosaccharide solution
b. Tube 2 = 30 drops of known disaccharide solution
c. Tube 3 = 30 drops of known polysaccharide solution
4.) Using a separate dropper, add 30 drops of BENEDICT’S solution into each tube.
5.) Place all three test tubes into how water bath for 5 minutes.
6.) CAREFULLY remove from bath (test tubes will be HOT) and observe any color changes. Record the
color changes in Data Table-1 under the heading “Benedict’s Color Change”
NOTE: A color change from blue to green, yellow, orange, red, brown occurs if monosaccharides are
present.
B. Iodine Test – Polysaccharide
1.) Number three clean test tubes: “1-mono”, “2-di”, and “3-poly”
2.) Using a new dropper, add 4 drops of IODINE solution to each tube.
3.) Mix the contents of each tube by gently swirling.
4.) Record the color of each test tube in Data Table-1 under the heading “Iodine Color Change”
NOTE: A color change from original rust to blue-black occurs if polysaccharides are present.
C. Testing Unknown Carbohydrates
1.) Number five clean test tubes: “1”, “2”, “3”, “4”, and “5”
2.) Add each of the following:
a. Tube 1 = 20 drops of honey
b. Tube 2 = 20 drops of liquid oats
c. Tube 3 = 20 drops of table sugar solution
d. Tube 4 = 20 drops of apple juice
e. Tube 5 = 20 drops of powdered sugar solution
3.) Add 30 drops of Benedict’s solution to each test tube.
4.) Place all five tubes into a hot water bath for 5 minutes and record any color changes in Data Table-2.
5.) Prepare 5 more test tubes (repeat steps 1 and 2)
6.) Add 4 drops of iodine solution to each tube and mix by swirling. Record any color changes in Data
Table-2.
Name:_____________________________________________
Date:_______________ P.________
CARBOHYDRATE LAB
What was the underlying problem/question/observation behind this investigation? ________________________
_________________________________________________________________________________________________________________________
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Predictions: Honey = _________________________________, Oats = _____________________________________
Table Sugar = _______________________________ Apple Juice = ___________________________________
DATA RESULTS
Test Tube #
1
2
3
Carbohydrate
Mono
Di
Poly
Carbohydrate
Honey
Oats
Table Sugar
Apple juice
Powdered sugar
Table-1
Benedict’s Color Change
Table-2
Benedict’s Test
Iodine Color Change
Iodine Test
DATA RESULTS :(summarize and restate data): ______________________________________________________________
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CONCLUSION (Discuss results and what they mean. Be sure to identify the unknown
carbohydrates. Use data to accompany your explanations. Identify and discuss any actual or
probable experimental errors. Identify and explain any unexpected results. Re-state hypothesis
or predictions and clearly explain reasons for rejecting/accepting your hypothesis or
predictions).
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POST-LAB QUESTIONS:
1.) What common name do we give carbohydrates?_____________________
2.) Name the 3 scientific categories of carbohydrates and give TWO examples of each.
a. __________________________________ 2 examples: ____________________________ and ____________________________
b. __________________________________ 2 examples: ____________________________ and ____________________________
c. __________________________________ 2 examples: ____________________________ and ____________________________
3.) What 3 elements are present in all carbohydrates? ____________________, ___________________, __________________
4.) “Mono” means ___________ and “di” means ____________ and “poly” means _______________. Why are these
terms used in describing the three types of sugars?_______________________________________________________________
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5.) What are the simple precursor molecules (monomers) of a polysaccharide? ____________________________
6.) Why did you perform tests on known substances?____________________________________________________________
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7.) How can you tell by using Benedict’s and iodine if a sugar is a…
a. monosaccharide____________________________________________________________________________________
b. disaccharide________________________________________________________________________________________
c. polysaccharide______________________________________________________________________________________
8.) A certain sugar has no change in color when tested with Benedict’s solution.
a. Can you tell which type of saccharide it is? ______________
b. Explain _____________________________________________________________________________________________________
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9.) A certain sugar has a color change in Benedict’s solution.
a. Can you tell which type of saccharide it is? ______________
b. Explain _____________________________________________________________________________________________________
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10.) Give examples (try for 3 each) of a food that is…
a. monosaccharide ___________________________________________________________________________________________
b. disaccharide _______________________________________________________________________________________________
c. polysaccharide _____________________________________________________________________________________________