Norwich School District
Grade 8 

 Core Activities
    Photochemical Reactions
    Chemistry of Ozone
    Diesel Bus Case Study in Connecticut
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Chemistry of Ozone
-> How is Ozone created?

In this activity, you will .

Procedure

1.  Break up into groups of 2 students.   Obtain a set of materials (a large sheet of paper and set of Post-it tabs, 30 red, 30 blue, 20 yellow) for each group.

2.  Place the red and blue post-its randomly on one half of the large sheet of paper, representing the atmosphere.

3.  Air is mostly nitrogen molecules and oxygen molecules.   Oxygen atoms will be represented by red post-its and Nitrogen atoms will be represented by blue post-its.  It may be helpful to mark the red post-its with an "O", and the blue post-its with an "N".

4.  The temperature inside engines causes the nitrogen molecules and oxygen molecules in the air inside the chambers to combine and form nitric oxide which is emitted to the atmosphere.  With the post-its, create 5 nitric oxide molecules.

N2(g) + O2(g)  heat >  2 NO(g)

5.  The nitric oxide emitted to the atmosphere quickly combines with more oxygen in the air to form nitrogen dioxide.   Add red post-its to create 5 nitrogen dioxide molecules.

2 NO(g) + O2(g)  --> 2 NO2(g)

6.  In warm, sunny air, the nitrogen dioxide breaks down into a molecule of nitric oxide and an atom of oxygen.  Break down the post-it molecules.

NO2(g)  light >   NO(g) + O(g)

7.  The atom of oxygen combines with a molecule of oxygen to form ozone, the form of oxygen that has 3 oxygen atoms in its molecule.  Rearrange the post-its to create the ozone molecules.

O(g) + O2(g)  ----->   O3(g)

8.  The nitric oxide reacts with the ozone to form nitrogen dioxide and an ordinary oxygen molecule.  Rearrange the post-its to form.

NO + O3 -----> NO2 + O2

9.  We’re back where we started.  As long as there’s sunlight, this cycle can repeat, and the ozone concentration will never get very high, since the ozone reacts with nitric oxide almost as fast as it is formed.

Part 2
10.  The cycle can be broken by other substances we add to the atmosphere.  For example, fumes from fuels, solvents from drying paint and from glue—all add volatile organic compounds (VOC's) to the air.  VOC's will be represented by yellow post-its.  It may be helpful to mark the yellow post-its with "VOC".  Add the yellow VOC post-its to the "atmosphere" randomly among the red and blue post-its on the paper.

11.  For example, the temperature inside engines causes the nitrogen and oxygen in the air inside the engine's chambers to combine and form nitric oxide (NO) which is emitted to the atmosphere.  With the post-its, create 5 nitric oxide molecules (NO).  Write the chemical equation.

12.  The nitric oxide emitted from the engine to the atmosphere quickly combines with more oxygen in the air to form nitrogen dioxide (NO2).   Add red post-its to create 5 nitrogen dioxide molecules (NO2).  Write the chemical equation.

13.  In warm, sunny air, the nitrogen dioxide (NO2) breaks down into a molecule of nitric oxide (NO) plus an atom of oxygen.  The  nitric oxide (NO) molecule then combines with a VOC molecule, leaving the atom of oxygen (O) free in the atmosphere.  Rearrange the post-its to reflect this reaction.  Write the chemical reaction.

14.  The atom of oxygen (O) combines with a molecule of oxygen (O2) to form ozone, the form of oxygen that has 3 oxygen atoms (O3) in its molecule. 

15.  Repeat steps 11 - 14.  Do you see a pattern emerging?  Answer the questions on the Student Worksheet.

 

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