| GK-12
Sensors!
Portable Module
Title: Schönbein Ozone Sensors
Author: Andrea Martin
Disciplines: All
Introduction
The objective of this lab is to introduce tropospheric ozone to the
students and allow them to measure ground-level ozone concentrations
with sensors that they make.
Associated Maine Learning Results
MLR J
Required Equipment
Atmospheric Environment, Vol. 33, 1999. p. 919-929
ChemMatters, September 2002. p. 8-9
Circular filter paper
Cornstarch
Distilled water
Overhead Transparencies
Paintbrushes
Potassium iodide
Procedure
- Cut a piece of circular filter paper into a one-inch strip.
- On an overhead transparency, paint the already-prepared potassium
iodide/cornstarch solution onto the filter paper strip. This is
an ozone sensor.
- Allow sensor to dry on transparency.
- Take sensor home.
- Before testing for ozone, lightly dip sensor in water.
- Place sensor in an ultraviolet light-free place for 8 hours.
- Bring sensor back to school.
- Lightly dip sensor in distilled water.
- Using the Schönbein color scale (Figure 1,
ChemMatters, September 2002. p. 8-9), assign a number (0-10)
that is equivalent to the color of the sensor.
- Using local weather data gathered by the instructor (www.weatherunderground.com),
determine the average humidity over the 8-hour testing period.
- Using Linvill’s chart (Figure 1,
Atmospheric Environment, Vol. 33, 1999. p. 921), determine
the non-normalized ozone concentration in ppb by following
the assigned Schönbein number up to the appropriate relative
humidity curve.
- Using Equation 2 (Atmospheric Environment,
Vol. 33, 1999. p. 921), calculate the normalized ozone
concentration. This is the average ozone concentration
detected over the 8-hours.
Expected results
For sensors placed indoors, the sensor’s color change should
not be very dramatic and should result in a concentrations ~5 ppb.
For sensors placed outdoors the concentrations may be around 20 ppb.
Troubleshooting
- If the sensor is not dry by the end of class, wrap it in parafilm
or cut up pieces of overhead transparencies so the students can
take sensors home.
- If students did not dip their sensors in water before leaving
them in the detection site, the sensors will not be able to react
with the ozone in the atmosphere.
References
Atmospheric Environment, Vol. 33, 1999. pp. 919-929.
ChemMatters, September 2002. pp. 8-9.
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