Radishes and Acid Rain
Acid rain is precipitation that has absorbed and reacted with compounds in the atmosphere to form acids. Acid rain is
defined as precipitation with a pH of less than 5.6, as precipitation with a pH of 5.6 or above is considered “normal”
precipitation. The term “acid rain” dates back to mid 1800s England. Following a long period of deforestation, homes
and business gradually converted to burning coal as a primary source of fuel. Scientists noticed that rain falling during
this time became more and more acidic. Eventually the connection between the increasing acidity and the combustion
of coal was made.
The chemicals primarily responsible for acid rain fall into two basic classes: Sulfur Oxides (SOx) and nitrogen oxides
(NOx). It is important to understand that acid rain is created both naturally and by man-made sources. The primary
natural sources for SOx are volcanoes, fires, wetlands and other systems with significant concentrations of anaerobic
bacteria. Man-made sources for SOx are the burning of coal, ore smelting and oil refining. Natural sources of NOx
include fires (high temperature combustion) and lightening. The most significant man-made sources of NOx are
automobile emissions.
The combustion of fossil fuels produces sulfur dioxide, and then in the atmosphere SO2 further oxidizes to form H2SO4
(sulfuric acid). Vehicle internal combustion engines combine nitrogen with oxygen to form nitric oxide (NO) which
then further reacts with oxygen to form nitrogen dioxide NO2. Ultimately nitrogen dioxide reacts with hydroxyl radicals
and ozone to form nitric acid (HNO3).
When acid rain comes in contact with plants and the surrounding soil, several things occur. Vital soil nutrients such as
potassium, calcium and magnesium react with the acid rain and are removed from the soil and transported away, or
become chemically unavailable to the plants. Acid rain also dissolves and frees up toxic metals in the soil such as
mercury, manganese, lead, zinc and aluminum, which are toxic to plant growth. As plants come into direct contact with
acid rain, the surface areas of leaves and stems become damaged and make the plants vulnerable to disease.
DRIVING QUESTION
 How do acid rain solutions of different pH values impact radish plant growth?
HYPOTHESIS
 If ___________________________ than ____________________________
(independent variable change)
(dependant variable change)

This is because __________________________
SAFETY
 Spraying acid solution in spray bottles is dangerous for the eyes! Goggles and good
judgment are a must!
MEASUREMENT
 What measurements need to be completed to evaluate the effect of acid rain concentrations on plant growth?
How will we determine growth and acidity of your acid solutions?
 What are your independent, dependant variables, and control? (Hint: one of the rain solutions has a pH of 7.)
PROCEDURE
1. Germinate seeds as directed on the green “growing Radishes” instruction sheet.
2. After 1 week, thin the radishes so that there are only three healthy seedlings growing in each pot. To thin,
CUT the radishes you don’t want with a small scissors - DON’T pull out by the roots, it will disrupt the root
systems of all the plants. Record the height of each plant on “day 0” in the data table. Measure from the soil
to the top of the seedling. Average the height of the plants as well, and record on day 0.
3. Put on your goggles. Using the spray bottle that matches the labeled marker in the radish plant (aka spray
bottle solution 2 should spray plant “Rain Solution 2”), ISOLATE the plant away from the other plants, and
spray 10 sprays on the plants, doing your best to evenly soak all the plants. Repeat with all plants.
4. You will need to take 4 more measurements of your plant height – discuss with your group who will make
the measurements, and at what time.
5. On the last day of the experiment, test the pH of the solutions with the pH probe.
PRELAB QUESTIONS
1.
2.
3.
4.
5.
6.
When and why was acid rain first observed?
What pH value is considered acid rain?
Sulfur dioxide is one of the two main atmospheric pollutants that cause acid rain. List one natural and one
man-made source of this atmospheric sulfur dioxide.
Nitrogen dioxide is the second of two main atmospheric pollutants that cause acid rain. List one natural and
one man-made source of this atmospheric nitrogen dioxide.
What happens when acid rain interacts with soil?
What happens when acid rain interacts directly with plant tissue?
SYNTHESIZED DATA
Data Table 1: Lab Group Data for Acid Rain and Radish Growth
Day
Rain Solution #1
1
2
3
Rain Solution #2
Ave
1
2
3
Rain Solution #3
Ave
1
2
3
Rain Solution #4
Ave
1
2
3
Day 0 Plant Height
(in cm)
Day 1 Plant Height
(in cm)
Day 2 Plant Height
(in cm)
Day 3 Plant Height
(in cm)
Day 4 Plant Height
(in cm)
pH of Solution
Data Table 2: Class Data for Acid Rain and Radish Growth
Day
Day 0 Plant Height
(in cm)
Day 1 Plant Height
(in cm)
Day 2 Plant Height
(in cm)
Day 3 Plant Height
(in cm)
Day 4 Plant Height
(in cm)
pH of Solution
Rain Solution #1
Rain Solution #2
Rain Solution #3
Rain Solution #4
Class Average
Class Average
Class Average
Class Average
Ave
DATA ANALYSIS
A. Graphs
Graph average plant height vs. number of days for each rain solution. You should have two graphs, one for
your group data and one for the class data.
B. Qualitative Data& Sketches
Make two qualitative observations about EACH set of solution treatment plants – did the leaves look
healthy, what color green were they, any mutations or burn marks in the plants? Draw a sketch or take a
picture of a seedling in each of the four treatment groups and include as well.
CONCLUSION
Discuss the following:
1. Answer the driving question
2. Summarize the results of the activity (what happened to plants with each rain treatment). Make sure to
include NUMERIC data in your discussion – ex. Acid rain solution 1 plants grew 2 cm less than the other
solutions
3. Describe if your hypothesis is correct.
4. Support your hypothesis conclusion with NUMERIC evidence from your experiment.
5. Discuss how your group data compared or differed from the class average data.
6. Real World – If an area’s crop growth is being impacted by acid rain, what is one thing either local
farmers or local law makers could do to try to minimize the current or future economic damage to the
crops?