Student Worksheet:
Name: _________________________________
Ozone Testing Tools
Group: _______________
Background
Christian Friedrich Schoenbein discovered ozone in 1839 in Switzerland. He developed a way to measure ozone in the troposphere using a mixture of starch, potassium iodide, and water spread on filter paper. Ozone causes iodide to oxidize into iodine, causing
Schoenbein paper, to change color when ozone is present. The iodine reacts with starch, staining the paper a shade of purple. The intensity of the purple color depends on the amount of ozone present in the air. The darker the color, the more ozone is present.
The reactions involved are:
2KI++ --> 2KOH++ + starch --> blue color
Note: this activity works best in areas of low humidity and high ambient ozone concentrations.
Materials:

hot plate

250 ml beaker

100 ml distilled water

1/4 teaspoon corn starch

glass stirring rod

1/4 teaspoon Potassium iodide

filter paper

small paint brush

Pyrex plate (optional)

paper or rack for drying filter paper

distilled water in spray bottle
PART A: CONDUCT THE INVESTIGATION:
1. Define a sampling objective, or the scientific question (hypothesis) you will address.
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Center for Innovation in Engineering and Science Education (CIESE) All Rights Reserved.
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2. Methods of Data Collection: Fill in the table below for each day data is collected
Location:
Duration:
(how long you will perform sampling)
Date(s) of
Testing
Wind
Speed &
Direction
Humidity
Events rain, fog, etc.
Temperature
(ºC)
1
2
3
4
5
3. Prepare Schoenbein Paper
NOTE: If your teacher has already prepared the chemical testing paper, go directly to 4.
Testing Procedure a. Place 100 ml of distilled water in a 250 ml beaker. b. Add 1 1/4 teaspoon of corn starch. c. Heat and stir mixture until it gels (thickens) and becomes somewhat translucent. d. Remove the beaker from the heat source and add 1/4 teaspoon potassium iodide. Stir well. Allow the solution to cool before applying to the filter paper. e. Lay a piece of filter paper on a glass plate, or hold it in the air, and carefully brush the paste onto the filter paper. Turn the filter paper over and do the same on the other side. Try to apply the paste as uniformly as possible. f. Wash hands after applying the potassium iodide mixture (Although potassium iodide is not toxic, it can cause mild skin irritation). g. Place the paper out of direct sunlight and allow it to dry. To save time, place the paper on a microwave-safe plate and microwave for one minute. h. Cut the filter paper into 1-inch wide strips. i. To store the paper, place the strips in a sealed plastic bag or glass jar out of direct sunlight.
Copyright © 2005 Stevens Institute of Technology,
Center for Innovation in Engineering and Science Education (CIESE) All Rights Reserved.
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4. Testing Procedure a. Spray a strip of test paper with distilled water and hang it at a data collection site out of direct sunlight. Make sure the strip can hang freely.

Note: Because relative humidity affects results, Schoenbein paper should not be left outside during periods of high humidity. b. Expose the paper for approximately eight hours. c. Observe and record test results immediately. Use the Schoenbein Color
Scale and Relative Humidity Chart to obtain an ozone reading. If the color change of the paper was not uniform, determine the Schoenbein Number by the color in an area with the most noticeable change.
Schoenbein Color Scale
0 - 3
4 - 6
7 - 10
Little to no change
Lavender hue
Blue or Purple
Test Result
ppb = AQI color d. Obtain the relative humidity for the local area. Round off the relative humidity reading to the nearest 10 percent. (Higher relative humidity makes the paper more sensitive to ozone, and a higher Schoenbein Number could be observed. To correct for this, the relative humidity must be determined and figured into the calculation of ozone concentration.) Refer to the Relative
Humidity Schoenbein Number Chart below. Along the bottom of the chart, find the point that corresponds to the Schoenbein number recorded from the paper. From that point, draw a line straight upward until it intersects with the curve that corresponds to your relative humidity reading. To find the ozone
Copyright © 2005 Stevens Institute of Technology,
Center for Innovation in Engineering and Science Education (CIESE) All Rights Reserved.
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concentration in parts per billion, draw a perpendicular line from the
Schoenbein number/relative humidity point of intersection to the left side of the chart.

Note: Please be aware of false positive test results that may occur from NOx in heavy traffic areas
This lesson was adapted from the University Corporation for Atmospheric Research,
Cycles of the Earth and Atmosphere module and the Environmental Resource Guide from the Air and Waste Management Association.
PART B: PART B: AIRNOW AND FINAL PRESENTATION
1. Access the AIRNow web site ( http://www.epa.gov/airnow/mapselect.html
) and obtain near real-time data for the area (if available).
2. How does the Ozone data you collected compare with the AIRNow data for your region? For example, is it similar or different? Be sure to include any reasons you think might influence this and identify possible sources of NOx and VOCs leading to the production of ground level ozone
Copyright © 2005 Stevens Institute of Technology,
Center for Innovation in Engineering and Science Education (CIESE) All Rights Reserved.
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3. As a concluding activity, each group will create and deliver a 5 minute presentation about the investigation they created and the data collected. Each presentation should contain the following information:

The sampling objective (hypothesis) for the investigation;

A description of the method of data collection, including the frequency, duration, and location of monitoring;

How did the different measurement tools compare?

How did the data compare with the AIRNow data? and

What are possible sources of ozone?
Copyright © 2005 Stevens Institute of Technology,
Center for Innovation in Engineering and Science Education (CIESE) All Rights Reserved.
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