Name _______________________________
Chemistry of Carbohydrates
Carbohydrates, fats, proteins, and nucleic acids are the four major groups of biomolecules found
in living organisms. Carbohydrates make up a large group of biomolecules found within the cell.
They are generally used for energy or cell structures.
Key Words: define these when you are finished with the lab.

Monosaccharide

Disaccharide

Polysaccharide

Carbohydrate

Molecular Formula

Structural Formula

Dehydration Synthesis
Materials
Each group should obtain the following plastic pieces that represent atoms of carbon, hydrogen
and oxygen.
Carbons—black
Oxygen—blue
Hydrogen—white
Bonds—plastic tubes
Water: The chemical formula of water is H2O. By examining this formula, some information
can be gained.
1. What elements make up water? ______________________________________________
2. What does the subscript number 2 following the H represent? ______________________
3. Why doesn’t the O have a subscript? __________________________________________
4. How many molecules of water are represented by the formula H2O? _________________
5. Build a structural model of water with the parts provided. How many bonds did you use?
6. Draw the structural model of water that you built.
II. Carbohydrates: an important group of biological compounds are the saccharides (the
sugars of carbohydrates). Carbohydrates contain carbon, hydrogen, and oxygen. Carbohydrates
are grouped into three main categories:
Monosaccharides
Disaccharides
Polysaccharides
Monosaccharides or simple sugars.
Glucose
Fructose
Galactose
1. Study the structural formulas of glucose, fructose, and galactose above. They illustrate
three different monosaccharides.
2. Construct two different models of the monosaccharides.
3. How many atoms of carbon are in each model? ________ Oxygen? _______ Hydrogen?
________
4. Write the molecular formula for glucose: _______________________________
5. Write the molecular formula for galactose: _______________________________
6. Write the molecular formula for fructose: _______________________________
7. Compare the number of hydrogen atoms to the number of oxygen atoms in each
monosaccharide. What is the ratio of hydrogen to oxygen? _______: ________
8. How does this ratio compare to the ratio in water? _______________________________
Disaccharides or double sugars.
Two monosaccharide molecules can chemically join together to form a larger disaccharide. For
example, when a glucose and a fructose join together, the disaccharide sucrose is formed.
Sucrose is also known as table sugar.
1. In your group, construct a glucose and a fructose model.
2. Attempt to join the two molecules. Will they stay together? ____________
3. It will be necessary to remove an –OH end (oxygen bonded to a hydrogen) from one
molecule and an –H end from the other molecule in order to join them. Now can you
connect the molecules?
4. The –OH and the –H ends that are removed combine to form a familiar molecule. What
is it? _________________
5. Count the number of carbons, hydrogens, and oxygens in your disaccharide. Write the
molecular formula: _____________________________
6. What is the ratio of hydrogen to oxygen in the disaccharide? _______: _________
Polysaccharides
When many monosaccharides are joined together, a polysaccharide is produced. Examples of
familiar polysaccharides are starch, glycogen, and cellulose. They are made up of 1000’s of
glucose molecules connected together.
Summary
1. Synthesis means the “process by which simple compounds are united to form more
complex materials.” Dehydration means the “loss of water.” Explain why chemists
refer to the joining of monosaccharides to form disaccharides as a dehydration synthesis
reaction
2. The word carbohydrate is derived from carbon and water (hydrate). Explain why this
combination correctly describes this chemical group.
3. Draw a structural formula of the disaccharide that you built:
Going Further
Examine the building blocks of a fat (a lipid) below:
1. The fat is made of _________ glycerol and __________ fatty acids.
2. The three fatty acids will connect to the glycerol to make a fat. How many waters are
lost when these connections are made? _______
3. Circle the areas on the molecules where these waters are lost. One has been done for
you.
4. Now draw the completed fat below: