Carbohydrate Chemistry _______________________________
Today, scientists use a combination of biology and chemistry for their understanding of life and
life processes. Thus, an understanding of some chemistry of living things is necessary.
Carbohydrates make up a large group of chemical compounds found in cells. Carbohydrates are an
energy source or are used in making cell structures.
In this investigation, you will
(a) learn how to write a simple empirical formulas for several carbohydrates.
(b) learn how to read a structural formulas for several carbohydrates.
(c) use models to construct the three main types of carbohydrates.
The models you will use in this lab activity will help you learn how smaller molecules can be grouped
into larger, more complex molecules. REMEMBER: The models do not represent the actual threedimensional shapes of the molecules.
Part A. Water Model
Examine the chemical and structural formulas for water.
1. What elements make up water? ____________________________________
2. What does the number 2 following the H tell you? _________________________________________
3. Why does the oxygen symbol (0) not have a subscript? ______________________________________
4. How many molecules of water are represented by the formula H20? ________________
5. If you had three molecules of water, how would that be represented? ____________
6.. What is a structural formula? ________________________________________________________
7. What information is included in the structural formula of water? ______________________________
8. What does the structural formula of water tell us? ________________________________________
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9. What do the lines between O and H in the structural formula of water represent?
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Another way water may be represented is shown here. We will use this way of representing water
throughout our study of different chemical compounds found in living systems.
Notice how two separate parts fit together like a puzzle to form the water molecule. This represents the
formation of covalent bonds between the atoms in the molecule.
Part B. Carbohydrate Models
There are three different groups of carbohydrates. They are called monosaccharides, disaccharides, and
polysaccharides. "Saccharide" means sugar.
Group 1. Monosaccharides (single molecule sugars)
A single molecule sugar is called a monosaccharide. The prefix "mono-" means one. However, the one molecule
can have different shapes due to a different arrangement of atoms. Three monosaccharides are glucose,
fructose, and galactose.
Examine the structural formulas of these three sugars (Figure 1) and answer questions 1 to 7.
1. What three chemical elements are present in
the three monosaccharides shown? (NOTE:
The letter "C" stands for carbon, "H" stands for
hydrogen, and "a" stands for oxygen.)
1. What three chemical elements are present in the three monosaccharides shown?
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2. How many atoms of carbon are present in a molecule of
glucose? _________
fructose? ________
galactose? ________
3. Add subscripts to the following to indicate the proper molecular formula.
Fill in the blanks by counting the total number of carbon, hydrogen, and
oxygen atoms in each molecule.
4. Are there two times as many hydrogen atoms as oxygen atoms
in a molecule of:
glucose? _________
fructose? ________
galactose? ________
5. Are there two times as many hydrogen atoms as oxygen atoms in a molecule of water? __________
Compare the structural formula of glucose to fructose.
6. Are they exactly the same in shape? ____________
7. Are they both monosaccharides? _____________
Group 2. Disaccharides (double molecule sugars)
Two monosaccharide sugar molecules can join chemically to form a larger carbohydrate molecule called a
double sugar, or disaccharide. The prefix "di-" means two. By chemically joining a glucose molecule with a
fructose molecule, a double sugar called sucrose is produced.
Use the page of paper models given to you by your teacher to complete this section.
Cut out a model of one glucose and one fructose molecule. CAUTION: Cut along solid lines only.
Do not cut out ALL the molecules, only one glucose and one fructose.
Attempt to join the two molecules like puzzle pieces. (refer to Figure 1 to see how they might fit together)
7. Do the glucose and fructose fit together easily to form a sucrose molecule? _______
In order to join the molecules, remove an –OH end from one molecule and an -H end from another.
Cut along dotted lines. DO NOT lose any pieces!! You must account for all the atoms you cut!
8. Does removing the -H and -OH ends now allow the molecules to fit together easily? ____________
9. The -H and -OH ends that were removed can also fit together with each other to form a
molecule. This new molecule has a formula of _______________ and is called __________________.
Calculate the molecular formula for sucrose by adding together
the molecular formulas for glucose and fructose and then
subtracting water, H20. Show your work in the box:
10. The molecular formula for sucrose is: ________________________
11. Tape or glue the models to show the two products of this reaction:
Glucose + Fructose 
Tape or glue the two products here and label them by name.
Different disaccharide molecules can be made by joining other monosaccharides in different combinations.
By chemically joining a glucose molecule with another glucose molecule, a double sugar called maltose is
formed.
Cut out and attempt to join the two new glucose model molecules like puzzle pieces.
12. What must be removed from the glucose molecules so that they easily fit together? ______________
Calculate the molecular formula for sucrose by adding together
the molecular formulas for two glucose molecules and then
subtracting water, H20. Show your work in the box:
The molecular formula for maltose is: ________________________
13. How does the formula for sucrose compare to maltose?
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14. Are there two times as many hydrogen atoms as oxygen atoms in a disaccharide? ______________
15. How many monosaccharide molecules are needed to form one sucrose molecule? ____________
16. How many monosaccharide molecules are needed to form one maltose molecule? ____________
17. Tape or glue the models to show the two products of this reaction:
Glucose + Glucose 
Tape or glue the two products here and label them by name.
Group 3. Polysaccharides (many molecule sugars)
Just as double sugars were formed from two single sugar molecules, polysaccharides are formed when many
single sugars are joined chemically. The prefix "poly-" means many.
Starch, glycogen, and cellulose are the three most common polysaccharides in biology. They consist of long
chains of glucose molecules joined together with covalent bonds.
Construct a starch molecule by joining three glucose molecules. This model will represent only a small part of
a starch molecule because starch consists of hundreds of glucose molecules.
1. What must be removed from the glucose molecules in order to have them easily fit together? ________
The simple formula for a polysaccharide is written as (C6H12O5)n. The n equals the number of times the
(C6H12O5) group is repeated. You can see this group as the middle glucose of your model.
REMEMBER: Both the -H and -OH ends of the middle molecule are missing.
2. Tape or glue the models to show the products of this reaction: (HINT: There are THREE products!!)
Glucose + Glucose + Glucose 
Tape or glue the three products here and label them by name.
CONCLUSIONS
1. What is the chemical formula for glucose? _______________________
2. What do the symbols and subscripts in the chemical formula mean?____________________________
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3. Fill in this table with an example of each of the three main types of carbohydrates.
Type of carbohydrate
Example
4. Why do glucose and fructose have different chemical properties even though they have the same
chemical formula? __________________________________________________________________
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5. Name two ways that monosacharides can be formed? _______________________________________
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5. How is a dissacharide formed?________________________________________________________
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6. List two polysaccharides made by plants and tell why the plant makes each one.
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