Making and Using Schoenbein Paper
Christian Friedrich Schoenbein discovered ozone in 1839 during his tenure as
a professor at the University of Basel, Switzerland. He used the reactivity
of ozone to measure its presence and demonstrate that it is a naturally occurring
component of the atmosphere. He developed a way to measure ozone in the troposphere
using a mixture of starch, potassium iodide, and water spread on filter paper.
The paper, called Schoenbein paper, changes color when ozone is present. Ozone
causes iodide to oxidize into iodine ().
This test is based on the oxidation capability of ozone. Ozone in the air will
oxidize the potassium iodide on the test paper to produce iodine. 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. In some parts of the country, this activity may not be very
- Students will understand that ozone is a gas found in the troposphere and
other parts of the atmosphere.
- Students will be able to demonstrate that by using Schoenbein paper, variations
in the amount of ozone present in the troposphere can be determined from day
to day and from place to place.
- Students will be able to explain that the Schoenbein paper detects ozone
by an oxidation reaction caused by the ozone in the surrounding air.
- Students will be able to draw conclusions about ozone levels of the air
based on test results.
Alignment to National Standards
National Science Education Standards
- Science As Inquiry, Grades 5 to 8, pp. 143: "Content Standard A: As
a result of activities in grades 5 - 8, all students should develop abilities
to do scientific inquiry and understandings about scientific inquiry."
Benchmarks for Science Literacy, Project 2061, AAAS
- Scientific Inquiry, all grades, pgs. 9-13.
- Grade level: 7 to 9
- Will vary depending on the nature of the student experiment, but each
exposure will take 8 hours
- Potassium iodide (a teaspoon will be plenty)
- Distilled water (must use distilled water)
- Spray bottle filled with distilled water (must use distilled water)
- Filter paper
- Heat source (preferably a hot plate)
- Corn starch
- Glass stirring rod (do not use metal)
- Small paint brush
- 250 ml beaker
- Glass Pyrex plate
- Hot pad or mitt for removing the beaker from the heat source
- 8 1/2 x 11 inch paper for drying filter paper
- Map of city or school building
Schoenbein Paper Preparation (For safety, you may want to prepare the paper
as a demonstration)
- Place 100 ml of distilled water in a 250 ml beaker.
- Add 1 1/4 teaspoon of corn starch.
- Heat and stir mixture until it gels. The mixture is gelled when it thickens
and becomes somewhat translucent.
- Remove the beaker from the heat source and add 1/4 teaspoon of potassium
iodide and stir well. Cool the solution before applying to the filter paper.
- 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
- Wash hands after applying the potassium iodide mixture. (Although potassium
iodide is not toxic, it can cause mild skin irritation.)
- Set the paper out of direct sunlight and allow it to dry. A low temperature
drying oven works well if available.
- Cut the filter paper into 1-inch wide strips.
- To store the paper, place the strips in a sealable plastic bag or glass
jar out of direct sunlight.
- Each student should be given at least two strips to test.
- 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.
- Expose the paper for approximately eight hours. Note where each strip was
- After exposure, seal the strip in an airtight container if the results will
not be recorded immediately.
- To observe and record test results, spray the paper with distilled water.
Observe the color.
Note: The xerographic process in most copy machines uses electrostatic charging
of a cylinder. The accompanying ionization creates ozone in adjacent air, so
a room containing a copy machine makes a good location for this experiment.
Teacher Note: Because relative humidity affects results, Schoenbein
paper should not be left outside during periods of high humidity.
Qualitatively Determine Ozone Level
- Have students compare their test strips. This is a qualitative comparison.
While numbers cannot be attributed to this test, you can make relative comparisons.
Those strips that show little or no change were in places with the lowest
ozone concentrations. Those that have a lavender appearance were exposed to
more ozone and, finally, those that look dark purple had high ozone exposures.
Questions and Observations
- What change in the test paper, if any, did you observe? (The paper will
vary in color depending on the amount of the oxidation. The color of the paper
may not be uniform.)
- Compare your test paper to those of your fellow students. Do all the test
papers appear the same? (The individual test papers will vary depending on
the amount of oxidants at various sites. For example, sites near highways
will show greater color change due to oxidants from car exhaust and nitrous
oxides in heavy traffic areas.)
- Was the relative humidity for your test day high or low? (The results of
individual test papers will vary depending on the specific relative humidity
of the site. See the reaction in the Background Information section. Notice
that water is a reactant, so humidity will affect the reaction. Sites near
lakes or streams may show greater change.)
- Why do you think the various test papers did not all appear the same? (Student
answers will vary. Tropospheric ozone levels vary widely due to the type and
number of sources of ozone. Students measuring ozone in their home may report
little color change of the paper, but if they live on a busy street, a measurement
near the curb will register greater color change. Humidity and oxidants are
present in varying levels depending on the time of day, the weather, the season,
- Based on the data you collected, do you think this method is a good way
to measure ozone in the troposphere? Why or why not? (Some students will point
out the difficulty in interpreting the color accurately, while others will
note the differences in how the paper was produced from group to group. It
is important to stress that this is a good method for measuring relative amounts
- Using a city or county map of your area, have students place sticky dots
corresponding with the color of the Schoenbein paper from the location for
which they collected data. Have students initial their dot.
- Compare data your students collect with those from a local monitoring station.
Also, if possible get information about the wind direction during your study.
- Have groups of students collect daily ozone data for a week. These data
can be plotted on a graph using parts per billion (ppb) on the vertical axis
and the days on the horizontal axis. The students can see if there is any
variability from day to day. By comparing the graphs, the students can see
if there is any consistency in their data and if so, try to come up with a
theory why. Students could also compare data to weather (temperature, relative
humidity, clouds, wind, rain, etc.)
- Contact your local Air Quality Control Board and request data for your test
week. Do your readings agree with those from the control board?
- It is always a good idea to get as many readings as possible. Incorporate
other grade levels and other schools. Contact the state Air Quality Control
Board for data during the test period. Compare data from students in different
cities and states. Do you see correlations or patterns?
Research Project: Construct an Ozone Map of Your Area
- Give each student two strips of Schoenbein paper in a sealed bag.
- Have students moisten the paper with distilled water and hang the test strips
at two sites in or near their home.
- Students should record their data noting the color change they observe.
Students can then plot relative ozone concentrations on a local map.
- Have students contour the map indicating areas of high and low ozone concentration.
- Was there any variation in ozone levels on the map?
- Where on the map were the concentrations the highest? The lowest?
- Looking at the area of highest concentration, does there appear to be any
obvious explanation for the variation?
- Why do you think there were ozone level variations?
- This would serve well as a scientific inquiry task and allow the teacher
to assess student understanding of ozone distribution as well as the students'
ability to design and conduct simple, independent experiments. A simple laboratory
report on ozone distribution would be an appropriate assessment tool.
Modifications for Alternative Learners
- English Language Limited (ELL) students should be able to carry out this
lab with little difficulty. If done as an inquiry task, all students should
be given clear and specific directions on how to write up the lab. Students
in general, and ELL students in particular, might benefit from a simulated
report example prepared by the teacher as a guide (particularly if they have
limited experience with inquiry lab reports).
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