Activity 1: Decomposing Sucrose

EXPLORATION:
1. Ordinary table sugar (sucrose) is a substance known as a carbohydrate.
  a. Have you ever been dehydrated? What do you think is the meaning of hydrated?

 
  b. What do you think a carbohydrate is? Note that it could also be called hydrated
     carbon.

2. Cookies, cakes and other baked goods contain carbohydrates. What happens when
  cookies and cakes are left in the oven too long?

3. You have probably roasted marshmallows over a fire.
   a. What do you think happens in the roasting process that turns a white marshmallow
     into a brown color or even into a black color?

   b. What happened to a marshmallow if it turns into a charcoal-like substance?

4. Sucrose has the formula of C₁₂H₂₂O₁₁. What is the lowest ratio of hydrogen to oxygen
  atoms in the formula? Explain why sucrose is a carbohydrate.

5. Separate C₁₂ from the rest of the C₁₂H₂₂O₁₁. molecule. Again explain why sucrose is called a carbohydrate.

Purpose: To decompose sucrose (C₁₂H₂₂O₁₁.) into carbon and water.

Materials needed:
  a. goggles
  b. sucrose
  c. aluminum foil scoop
  d. matches

Procedure:
 a. Place a tiny (matchhead size) amount of sucrose on one end of an aluminum foil scoop.
 b. Place the end of the scoop with the sugar 1/2 cm above the tip of the flame which is
  the hottest part of the flame.
 c. Heat gently at first. Avoid placing the scoop into the flame because that causes sooting.

            Wear goggles!
 

6. Write your observations in the space below.

7. What do you think the black residue is?

8. Perhaps you noticed steam emitted during the decomposition. What do you
  think is the chemical formula for steam?

EXPLANATION:
  You were correct if you stated that a carbohydrate such as sugar when heated
  decomposes into carbon atoms and water; the hydrated part of the molecule. Other
  names for carbon (symbol C) produced in this chemical reaction are soot or carbon
  black. In a decomposition reaction, the reacting substances are broken down into
  smaller molecules and/or atoms which recombine into products with new chemical
  and physical properties. This is like demolishing a brick house then using the bricks
  to build a new structure. In a decomposition reaction molecules decompose into
  other substances as shown by the equation:

                           AB --> A + B

  The reactant AB (composed of part A and part B) in a chemical reaction is the starting
  material located on the left side of the equation. The products A and B are located on
  the right hand side of the arrow. They have totally different chemical and physical
  properties than AB when they are combined in the chemical equation.

  A chemical formula is a shorthand way of using symbols of atoms to identify
  molecule. For example the molecule sucrose is shown by the formula C₁₂H₂₂O₁₁.
  C, H, and O are the symbols for carbon, hydrogen, and oxygen atoms. A symbol
  represents an atom and consists of a capital letter and at times a second letter in
  the lower case. A chemical equation is a shorthand way of using formulas to show
  reactants and products. Reactants are written to the left of the -->. The arrow means
  "produces or yields" and is like an equal sign in a mathematical equation. The product
  or products are to the right of the arrow.

  Compounds and elements are the materials we see and touch in the laboratory. A
  pure element is made up of one kind of substance which cannot be broken down or
  decomposed into a simpler substance. A pure element is thought to be made
  up of billions upon billions of the same kind of atoms. Elements are considered to be
  the basic building blocks of matter. A pure compound is made up of two or more
  elements that can be broken down or decomposed into its elements or into smaller
  compounds. A pure compound is thought to be made up of billions upon billions of
  the same kind of molecules. The known number of compounds in the world is
  impossible to determine since there are many different possible combinations in
  which elements can combine.

  A theory or thought statement explains matter in terms of concepts such as atoms
  and molecules which cannot be seen or touched. A theory may or may not be true
  and is only valuable (and famous) if its explanations are accepted by many scientists.
Theory:
elements are made up of one kind of substance that cannot be created nor destroyed or be decomposed.
 atoms cannot be created nor destroyed or decomposed; from the Greek atomos - meaning indivisible; can't be divided compounds are made up of two or more elements which can be decomposed into elements or smaller compounds.
 molecules are made up of two or more atoms; can be decomposed into atoms or smaller molecules.
 

9. Relate the decomposition of sucrose to the three terms of the equation AB --> A + B.

10. Use a circle to write the formula for sucrose.  Use small circles with the symbol C inside to account for all of the carbons in sucrose. Use darkened circles for oxygen connected to 2 very small circles
    with H inside for hydrogen to account for all of the water molecules in the formula.

C₁₂H₂₂O₁₁.molecule                                             C atoms in sucrose                         H₂O molecules
 

11. Use the information above to complete the equations of the decomposition of sugar.
 
 

12. The sucrose molecule has the formula C₁₂H₂₂O₁₁. How many molecules of
    water (H₂O) are produced for every molecule of sucrose that is decomposed?

13. If the aluminum foil scoop is placed inside the candle flame, soot or carbon black
   begins to form. What do you think is soot and what do you think is its source?

14. Why do you think soot appears when the scoop was placed in the flame whereas
    soot would not appear or to a much lesser amount if the scoop is not placed in the
    flame?