Chemical Reactions: Combination	NAME
(THE COMBINING OF ATOMS AND	PERIOD    DUE DATE
MOLECULES TO FORM NEW COMPOUNDS)	LAB WRITE-UP GRADE

Activity 1: Combining Copper and Oxygen

EXPLORATION:
1. Oxygen (O₂) gas is approximately 1/5 or 20% of the air we breathe. List a number of
  ways in which oxygen is important to our lives and our economy?

2. List a number of ways in which oxygen gas is harmful to our lives and our economy?

EXPLANATION:
  Oxygen is a powerful chemical agent because it has the ability to oxidize or to
  combine with many chemicals. Oxygen (O₂), as a gas, liquid, or mixed in air
  destroys bacteria, reacts with foods in our bodies to give us heat and energy,
  combines with fuel in cars or helps to send rockets into outer space. Oxidation is
  the combination of oxygen with another substance such as a metal or nonmetal.
  Since oxygen combines with other substances, oxidation is a combination reaction.
  In a combination reaction two or more chemicals combine to form a new
  compound or compounds.

                        Example: A + B --> AB

  In the equation, A and B are atoms or molecules that react with one another and
  are called reactants. Chemical AB (made of parts A and B) is the result of the
  reaction called the product.

  In general, we think of the oxidation of iron as rusting however all other metals
  such as copper, aluminum, zinc, etc., oxidize meaning that they combine with
  oxygen. Aluminum oxidizes to a dull, gray color; silver oxide is black; and zinc
  oxide is white. Even water (H₂O) is an oxide of hydrogen. We don't think of metal
  oxides as rust but call them "tarnish." Tarnish, like rust, is the product of the
  combination of oxygen with a metal.

  All oxidation reactions produce heat. Rapid oxidation produces so much heat that
  we can see it as a flame. A fuel is an oxidizable substance because it can burn,
  that is, it has atoms that can combine with oxygen. Water (H₂O), sand (SiO₂), and
  carbon dioxide (CO₂) can be used to put out fires because they don't burn; they are
  already oxidized and very strongly bonded with oxygen.

EXPLORATION:
3. What do you think is the color of the oxide of copper (copper oxide, CuO)? (Think of an
  old copper penny)

4. Will heating an object affect the speed of a reaction with oxygen? Circle:
  (a) the reaction will be faster,
  (b) the reaction will be slower, or
  (c) heating will have no effect on the speed of a reaction?
     Explain why you think so?

EXPLANATION:
  The speed of a reaction increases with increased heat because molecules move
  faster. Faster moving molecules hit other reacting molecules harder and cause
  their breakup by first stretching then breaking the bonds between the atoms of the
  reacting molecules. The pieces from the collisions then recombine into more stable
  molecules which are the products of chemical reactions.

Purpose: To heat copper in air to allow the hot metal to combine with oxygen
  molecules (O₂) in the air.
Materials needed:
  a. copper wire or copper strip approximately 10 cm long   
  b. steel wool or sand paper
  c. candle and matches
  d. goggles

Procedure:   a. Clean a bare piece of copper with either steel wool     or sand paper then record the color of clean copper     in the table below.   b. Wrap a piece of paper toweling on one end of the     wire to keep your fingers from getting hot.   c. Hold the bare end of the wire approximately 1/2 cm     above the tip of the candle flame which is the     hottest part of the flame.     CAUTION: Heating the wire inside the flame causes              sooting.                   Wear goggles!

  d. After heating the wire, allow it to cool, then use a piece of paper to wipe off any
    particles of soot accidentally on the wire. Record the colors in the boxes below.

        Data Table: Colors of Reactants and Products

color or clean copper metal (Cu)

color or oxygen (O2) gas in the air

color of copper oxide (CuO)

5. Explain why the copper oxidized faster when heated in a flame than when held in air
  at room temperature?

6. Use small circles with the Cu symbol inside and a darkened circle for O to draw
  pictures of atoms and molecules in the boxes below. Use a line or allow circles to
  touch to indicate bonding. The formulas are correct as shown. copper atoms (Cu)

7. Use the information from above to complete the equations of the oxidation of
  a shiny piece of copper when heated in air to produce copper oxide.

   

EXPLORATION:
8. Perhaps you have built a campfire as a scout or with your family. What three things
  do you generally need to build a camp fire?

9. How is the oxidation of wood in the campfire or fireplace:
    a. the same as the oxidation of the copper wire?

    b. different from the oxidation of the copper wire?

EXPLANATION:

Scouts know that a fuel such as wood, a kindling temperature, and oxygen are needed to build a fire. That is why the drawing on the left is called a fire triangle. Holding a shiny piece of copper in air will cause it to be oxidized very slowly. Heating a copper wire and the air around it provides the energy for all of the molecules to react by increasing the speed of the molecules and the energy at which they collide. The temperature created by a match usually provides sufficient collision energy for the molecules of oxygen to react with fuel molecules. Lighting a match or lighting small pieces of wood is called creating the kindling temperature which gets

  the fire going. The match does not have sufficient kindling temperature for example, to cause
  metal to rapidly oxidize or to burn with a flame. Once a fire creates its own heat, it sustains
  continued oxidation. Kindling temperature is called activation energy by chemists. Activation
  energy means that the molecules are moving fast enough so that when they collide the collision
  is hard or energetic enough to break the bonds holding oxygen and fuel molecules together so
  that a new product or products with stronger bonds is produced. Water (H₂O), sand (SiO₂),
  carbon dioxide (CO₂) are strongly bonded products of such oxidation reactions.

  The wood in a campfire can char indicating low heat, low molecular motion and
  slow oxidation that produces smoke and much soot. Soot is the unburned or
  unoxidized carbon in wood. Wood also burns rapidly with a bright flame producing
  carbon dioxide with little soot and smoke. The heated wood in a flame burns much
  more quickly because molecules are moving faster and are colliding harder causing
  them to react quickly and effectively. An oxidation, slow or fast, will proceed if all
  of the elements of the fire triangle are present. If any one of the three elements of the
  fire triangle is missing or removed, oxidation ceases and the fire stops burning.
  Answer the following questions below with the fire triangle in mind.

10. Perhaps you have learned that if your clothing is accidentally set on fire, you
    should STOP, DROP, AND ROLL. The purpose of STOP, DROP, AND ROLL
    is to:
        a. remove fuel such as your clothing
        b. remove oxygen to smother the flames
        c. lower the kindling energy.
    Explain.

11. Explain why water (H₂O), sand (SiO₂), and carbon dioxide (CO₂) are not fuels
   and can be used to put out fires.

12. Explain why fire fighters add water (H₂O), to put out fires. Think of kindling
   temperature.

13. Explain why fire fighters use grappling hooks to collapse a burning house on
   itself to stop a fire.

14. Why does blowing air with your mouth make glowing pieces of wood in a camp
   fire burst into flames?

15. Humans need oxygen to live. Where does our oxygen come from?

Chemical Reactions: Combination	NAME
(THE COMBINING OF ATOMS AND	PERIOD    DUE DATE
MOLECULES TO FORM NEW COMPOUNDS)	LAB WRITE-UP GRADE

Activity 2: Removing the Oxide (Tarnish) from Copper Oxide on a Penny

EXPLORATION:
1. What could you do to remove oxygen in the form of black oxide called tarnish
  from a copper wire or from an old penny so that it looks new again? That is,
  what kind of atom could you use to combine with the oxygen in a chemical
  reaction? And, what kind of molecule would be formed?

EXPLANATION:
  You were correct if you said that hydrogen can combine with oxygen in the oxide
  to form water (H₂O). Tarnish remover is a watery paste and many molecules in
  water solutions break up into positively and negatively charged pieces called ions.
  Metal atoms and hydrogen atoms form positive ions while nonmetal atoms generally
  form negative ions. Thus, positive hydrogen ions (H¹⁺) combine with negative oxide
  (O^2-) ions to form neutral water (H₂O). Copper metal for example has a red brown
  color whereas its copper ion in water is blue. We will be using three different
  "acids" in the next activity to supply hydrogen (H¹⁺) ions to remove tarnish. An
  acid is a chemical that releases hydrogen ions in water. The acids that we will
  use are (a) hydrochloric acid (H¹⁺Cl^1-) used in cleaning bricks and also called
  muriatic acid, (b) vinegar (CH₃COO^1-H¹⁺) used in cooking, and (c) water (H₂O).
  We generally don't think of water as an acid, but it does provide H¹⁺ ions.
  Think of it as a very, very, very weak acid.

2. Which liquid do you think is the strongest acid, providing the most H¹⁺ ions and
  therefore is the best cleaner of oxides from metals.
  a. hydrochloric acid (H¹⁺Cl^1-)   b. vinegar (CH₃COO^1-H¹⁺)    c. water (H₂O)
    Explain.

Purpose: To combine hydrogen ions from acids with oxide ions from tarnish to
  produce H₂O.

Materials needed:
  a. three blackened copper pennies
  b. liquids: water, vinegar, dilute HCl acid (0.1M concentration)
  c. eyedroppers or Beral pipettes for each liquid
  d. tooth picks for stirring

Procedure:
  Place three well-used, blackened pennies in a row, then put a drop from a different
  liquid on each penny. Use a tooth pick to stir to help the reaction between H¹⁺ ions
  and the black oxide on the penny. Record your observation in the table below.

  Data Table: Combination of H¹⁺ ions with Oxide (O^2-) Ions in Copper oxide

source of H1+ ions	observations	oxide removal none / better / best
water H2O
vinegar CH3COO1-H1+
muriatic acid: H1+Cl1-

 
3. All three solutions contain hydrogen ions. Based on the above results, which solution
  has the strongest concentration of hydrogen ions? Explain.

4. Use small circles with the Cu symbol inside, a darkened circle for O, a smaller
  circle with H inside, and a very small H inside a circle with a + sign for H¹⁺ ions
  to draw the pictures below.

  

5. Use the information above to complete the equations of the removal of the
  oxide in copper oxide to produce water and copper atoms. Use the circles of
  atoms and molecules for the picture portion of the equation.  

 

 

Chemical Reactions: Combination	NAME
(THE COMBINING OF ATOMS AND	PERIOD    DUE DATE
MOLECULES TO FORM NEW COMPOUNDS)	LAB WRITE-UP GRADE

Activity 3: Combining Atmospheric Oxygen (O₂) with Iron to Form an Oxide

EXPLORATION:
1. Rusting or oxidation of iron and steel causes enormous damage in our society. What
  do you think can be done to prevent rusting around the house?

2. Predict if heating has an effect on the speed of oxidation such as the rusting of
  iron? Do you think heating will (circle):
  a. speed up oxidation   b. slow down oxidation   c. have no effect on oxidation
    Explain why:

 

Purpose: To compare the speed of oxidation of   steel wool when exposed to the air and when   heated over a candle flame. Materials needed:   a. paper clips or tweezers and paper toweling   b. steel wool   c. candles and matches   d. goggles   e. aluminum foil approximate size: 20cm x     20 cm square Procedure:

a. Wad steel wool tightly into two balls so that    each ball has a diameter approximately the size    of penny. b. Place one steel wool ball in air to allow it to rust    or oxidize at room temperature. c. Place a lighted candle into the center of the large    20cm x 20 cm aluminum square to catch hot    steel wool pieces. Wear goggles! d. Spear the other steel wool ball on the "hook" end of   a straightened paper clip and heat it approximately   1/2 cm above the flame; the hottest part of the flame.

  Avoid heating the steel wool inside the flame since this adds soot to the steel wool
  rather than the oxide. Wrap paper toweling around the paper clip handle to keep
  your fingers from burning. Predict, then write your results in the table below.

       Data Table: Speed of Oxidation or Rusting of Steel Wool.

type of exposure to oxygen from the air	prediction: the speed of the oxidation is   slow /  fast	prediction is accepted / rejected
at room temperature
heated in a candle flame

Purpose: To determine if oxidation causes an increase in mass.

3. When iron rusts, do you expect it to (circle):
   a. increase in mass b. decrease in mass c. remain the same mass
     Explain

Materials needed:   a. Armchair chemistry balance   b. 5 mL syringe and eyedropper   c. paper clip hooks or tweezers and paper     toweling   d. steel wool   e. candles, matches and goggles   f. aluminum foil, 10cm x 10cm square   g. aluminum foil, 20cm x 20cm square. Procedure:

a. Construct a hat of aluminum with the    small 10cm x 10cm square so that    the crown of the hat just fits and is held    by the load cylinder of your balance. b. Tightly wad steel wool into four balls    as before so that each ball has a diameter    approximately the size of a penny.    Place  all four steel wool balls in the    aluminum hat in the balance. c. Determine the mass of the steel wool and   the aluminum by placing water with an   eyedropper into the countermass side

    until the balance is level. Remove the water with the 5 mL syringe and record the
     volume as mass in the tables below. Note: 1 mL water = 1 gram.
                            Wear goggles!
  d. Place the candle into the center of the large 20cm x 20cm aluminum square to
    catch hot steel wool pieces. Spear each steel wool ball on the "hook" end of a
    straightened paper clip and heat it approximately 1/2 cm above the flame; the
    hottest part of the flame. Avoid heating the steel wool inside the flame since this
    adds soot to the steel wool rather than the oxide.
  e. After a steel wool ball is thoroughly heated, allow it to cool, then place it and all
    of the oxidized steel wool balls into the up-side-down aluminum hat.
  f. Determine the mass of the aluminum and the oxidized steel wool balls again by
    using an eyedropper to place water into the countermass side of the balance until
    level. Remove the water with the 5 mL syringe and record the volume in the
    tables below as its mass in grams.

    Data Table: Mass of Steel Wool in Up-Side-down Aluminum Hat

predicting the mass will:	mass in grams before heating	mass in grams after heating	predicting the change of mass is:
a. increase b. decrease c. remain the same			a. accepted b. rejected c. can't be concluded

              Class Data Table: Mass of Steel Wool  

4. Why should you expect that the mass of the steel wool increases when heated in air?
  Explain

5. Use small circles with the Fe symbol inside and a darkened circle for O, then draw
  pictures of atoms and molecules that could be formed when iron and oxygen combine.
  Use a line or allow circles to touch to indicate bonding. Fe atoms do not bond directly
  with other Fe atoms but bond with one or more oxygen atoms. Place the picture
  drawings in the boxes below. The formulas of atoms and molecules are correct.

 
6. Use the above information above to complete equations to show how Fe atoms
  and O₂ molecules combine to form iron oxide (FeO) molecules.

7. Use the above information above to complete the equations to show how Fe atoms
  and O₂ molecules combine to form different iron oxide (Fe₂O₃ ) molecules.
   

8. The law of conservation of mass (or matter) states that the mass before a reaction
  equals the mass after a reaction. Explain why the law of conservation of matter has
  not been violated even though the steel wool increased in mass when heated.

9. Suppose that scouts provide logs with a mass of 10 kilograms to build a camp fire.
  At the end of the camp fire only a handful of ashes are left with a mass of less than
  one kilogram. Where did the mass go? Explain why the law of conservation is
  not violated.

Chemical Reactions: Combination	NAME
(THE COMBINING OF ATOMS AND	PERIOD    DUE DATE
MOLECULES TO FORM NEW COMPOUNDS)	LAB WRITE-UP GRADE

Activity 4: Application and Reflection
1. To change steel wool one can use a pair of scissors to cut it into little pieces. Steel
  wool can also be changed by burning it to produce iron oxide. Which change does
  not change steel wool? Which changes steel wool into another substance so that
  it is no longer steel wool? Explain.

EXPLANATION:
  Changes that do not produce a new substance or substances are physical
  changes. Cutting steel wool, breaking a piece of wood, evaporating or freezing
  water produce no changes in the basic composition of matter and are physical
  changes. Changes that produce new substances with new and different chemical
  properties such as when paper burns, milk sours, metals rust or tarnish are
  chemical changes.

2. Copper oxide (CuO) is a black substance. Explain why removing oxygen from the
  oxide to make a copper penny shiny is a chemical change.

3. To live, you must constantly breathe in air and take in food. Is the process of living a
  physical change or a chemical change? Explain.

4. The human body maintains an average body temperature of 98.6 degrees
  Fahrenheit. Where does the heat come from to maintain body temperature?

5. What is the advantage of maintaining a high body temperature in humans,
  dinosaurs, birds, etc., when compared to cold-blooded animals such as
  amphibians?

Chemical Reactions: Combination	NAME
(THE COMBINING OF ATOMS AND	PERIOD    DUE DATE
MOLECULES TO FORM NEW COMPOUNDS)	LAB WRITE-UP GRADE

 
VOCABULARY

1.  oxidation:

2.  combination reaction:

3.  reactant:

4.  product:

5.  tarnish:

6.  rapid oxidation:

7.  fuel:

8.  fire triangle:

9.  kindling temperature:

10. activation energy:

11. soot:

12. ion:

13. acid:

14. physical change:

15. chemical change:

(C) "Armchair Chemistry for the Middle Grades 2001"