It's Raining, It's Pouring: Chemical Analysis of Rainwater

Posted by Crevolt at 10:16 AM

Objective

The goal of this project is to assess the water quality of rainwater collected from different geographical areas. The water quality measures used in this project are hardness, pH, and plant growth. Additional measures could be chosen to expand this project.

Introduction

Is the chemistry of rainwater from different geographical regions similar or different? How does rainwater chemistry relate to that of local surface water? How is rainwater chemistry affected by large-scale weather patterns? Does rainwater chemistry affect the growth of plants? These are some of the many questions you could choose to pursue with this project.

This project is based on Jonathan Allison's 2003 California State Science Fair entry. Here is how Jonathan summarized his experimental procedure: "I contacted friends and family from 11 different cities in the United States and asked them if they could help me by collecting rainwater from their city. After they collected it, they shipped it back to me. Then I tested the rainwater for hardness, using the chemical process of titration. Next I tested the rainwater for pH levels. Then I planted radish seeds in potting soil and watered each set of seedlings with rainwater from a different city. I observed, measured and recorded any growth or changes daily for seven days." (Allison, 2003)

Water Hardness

Water hardness is a measure of dissolved compounds (e.g., magnesium carbonate, calcium carbonate) in the water. These compounds can precipitate out in boilers and water heaters (scaling). Hard water makes less suds with soap and detergent, so you need to use more soap and detergent to get clothes and dishes clean with hard water. General guidelines for classification of waters are: 0 to 60 mg/L (milligrams per liter) as calcium carbonate is classified as soft; 61 to 120 mg/L as moderately hard; 121 to 180 mg/L as hard; and more than 180 mg/L as very hard (USGS, date unknown).

Figures 1 and 2 show USGS water hardness data for the continental United States. Figure 1 is a histogram showing the mean hardness data for each of the 344 stations sampled. Figure 2 is a map of the U.S., showing the regional patterns of groundwater hardness. In both cases, the data is from 1975, but the patterns shown have proven to be stable over time.

Histogram of U.S. groundwater hardness from 344 collection stations.
Figure 1. Histogram of U.S. groundwater hardness from 344 collection stations (USGS, 1975 data).

Map of U.S. groundwater hardness from 344 collection stations.
Figure 2. Map of U.S. groundwater hardness from 344 collection stations (USGS, 1975 data).

pH

Acidity and alkalinity are measured with a logarithmic scale called pH. pH is the negative logarithm of the hydrogen ion concentration:

pH = −log [H+] .

What this equation means is for each 1-unit change in pH, the hydrogen ion concentration changes ten-fold. Pure water has a neutral pH of 7. pH values lower than 7 are acidic, and pH values higher than 7 are alkaline (basic). The table below has examples of substances with different pH values (Decelles, 2002; Environment Canada, 2002; EPA, date unknown).

Table 1. The pH Scale: Some Examples
pH ValueH+ Concentration
Relative to Pure Water		Example
010 000 000battery acid
11 000 000sulfuric acid
2100 000lemon juice, vinegar
310 000orange juice, soda
41 000tomato juice, acid rain
5100black coffee, bananas
610urine, milk
71pure water
80.1sea water, eggs
90.01baking soda
100.001Great Salt Lake, milk of magnesia
110.000 1ammonia solution
120.000 01soapy water
130.000 001bleach, oven cleaner
140.000 000 1liquid drain cleaner

Figure 3 shows a map of the average pH of precipitation in the continental U.S. for the year 1992. "The areas of greatest acidity (lowest pH values) are located in the Northeastern United States. This pattern of high acidity is caused by the large number of cities, the dense population, and the concentration of power and industrial plants in the Northeast. In addition, the prevailing wind direction brings storms and pollution to the Northeast from the Midwest, and dust from the soil and rocks in the Northeastern United States is less likely to neutralize acidity in the rain." (USGS, 1997)

Map of U.S. annual average precipitation pH (1992 data).
Figure 3. Map of U.S. annual average precipitation pH for 1992. (USGS, 1997).

Plant Growth

Most plants prefer soil that is near neutral pH. There are particular varieties (strawberries, azaleas and rhododendrons, for example) that prefer acidic soil. Soil pH also influences how readily available many soil nutrients are to plants.

Terms, Concepts and Questions to Start Background Research

To do this project, you should do research that enables you to understand the following terms and concepts:

  • titration,
  • water hardness,
  • pH.

More advanced students will also want to understand the following terms and concepts:

  • molarity,
  • stoichiometry.

Bibliography

Materials and Equipment

  • This project requires planning ahead. Remember that it will take some time for your volunteers to collect samples and send them to you. You also need to allow time (at least one week) for the plant growth experiment once you have received all of the samples. Start early and make sure your volunteers send their samples in a timely manner!
    • Where to get samples? You will need to obtain rainwater samples from a wide geographical area. Consult the maps in the Introduction for historical patterns of variation. Ask friends and relatives to collect samples for you.
    • How much water do I need? Check your test kit instructions (see below) to see how much water is required for each test (usually about 5 ml). You will want to repeat your tests for each sample at least 3 times to assure that your results are consistent. So you'll need a minimum of 30 ml just for testing (best to plan on more). You will also need water for the plant growth experiment. Calculate how much water you will need for plant growth, and add 50 ml for testing purposes. This is how much rainwater each of your volunteers will have to send to you.
    • How should my volunteers collect rainwater samples? Simply putting a jar out on the lawn during a rainstorm is not going to be very efficient. In order to get enough water, your volunteers need a large catchment area. Probably the most straightforward solution is to collect water from the roof, by placing a collection jar underneath a downspout.
    • Make sure your volunteers label the water sample with the date and location from which it was collected.
  • For performing the water quality tests, the simplest method is to use a pre-packaged kit designed for testing aquarium water. There are several different brands available. You should be able to find a choice at a local pet store that sells fish. The kit will say how many water samples it will test. You should be able to find kits to test 50 samples for under $10. The kits you need for this project are:
    • general hardness (GH) test kit,
    • pH test kit.
  • For the plant growth experiment, you'll need:
    • radish seeds, (or other suitable, fast-growing seeds),
    • small containers (peat pots or seedling trays),
    • potting soil, and
    • a measuring device for dispensing water.

Experimental Procedure

  1. For the water hardness and pH tests, follow the instructions that come with the water test kit. When titrating samples, it is important to mix the solution well after each drop of test solution is added.
  2. For the plant growth portion of the experiment, it is important to keep all of the other growth conditions (sun exposure, soil, temperature, etc.) constant, and to vary only the source of water used for the plants. Be sure to use the same amount of water. Consult the Science Buddies resource, Measuring Plant Growth for methods you can use to quantify differences in growth.

Variations

  • Does rainwater chemistry in your area vary with weather patterns? Collect samples over several weeks or months, and test the water quality. Keep track of the weather systems that produced the precipitation. Were there variations in the ultimate source of the moisture? Can you correlate these variations with changes in rainwater chemistry?
  • If you live in an urban area, is rainwater chemistry affected by smog? Check the air quality reported in the newspaper for the days that samples were collected. Do you see differences in rainwater chemistry after days with high smog compared to days with cleaner air?
  • For the samples in your study, how does rainwater hardness compare with groundwater hardness? (See Figure 2 in the Introduction, above.) How does the acidity compare to the 1992 U.S. data? (See Figure 3 in the Introduction, above.)
  • Here are two related Science Buddies projects you might want to check out:

Credits

Andrew Olson, Ph.D., Science Buddies

Sources

This project was based on:

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How Does Soil Affect the pH of Water?

Posted by Crevolt at 10:14 AM

Objective

The objective of this experiment is to measure how contact with different types of soil changes the pH of water.

Introduction

The level of acidity or alkalinity of a soil is one indicator of the soil's health and suitability for growing particular types of plants. Acidity and alkalinity are measured with a logarithmic scale called pH. pH is the negative logarithm of the hydrogen ion concentration:

pH = −log [H+] .

What this equation means is for each 1-unit change in pH, the hydrogen ion concentration changes ten-fold. Pure water has a neutral pH of 7. pH values lower than 7 are acidic, and pH values higher than 7 are alkaline (basic). The table below has examples of substances with different pH values (Decelles, 2002; Environment Canada, 2002; EPA, date unknown).

Table 1. The pH Scale: Some Examples
pH ValueH+ Concentration
Relative to Pure Water		Example
010 000 000battery acid
11 000 000sulfuric acid
2100 000lemon juice, vinegar
310 000orange juice, soda
41 000tomato juice, acid rain
5100black coffee, bananas
610urine, milk
71pure water
80.1sea water, eggs
90.01baking soda
100.001Great Salt Lake, milk of magnesia
110.000 1ammonia solution
120.000 01soapy water
130.000 001bleach, oven cleaner
140.000 000 1liquid drain cleaner

Most plants prefer soil that is near neutral pH. There are particular varieties (strawberries, azaleas and rhododendrons, for example) that prefer acidic soil. Soil pH also influences how readily available many soil nutrients are to plants.

In this project, you will measure pH values of different types of soils, and you will see how the soil affects the pH of water that comes in contact with it.

Terms, Concepts and Questions to Start Background Research

To do this project, you should do research that enables you to understand the following terms and concepts:

  • pH,
  • soil types

Questions

  • What value of pH is neutral?
  • What range of pH values is acidic?
  • What range of pH values is basic?

Bibliography

Materials and Equipment

To do this experiment you will need the following materials and equipment:

  • soil/water pH meter, with resolution of ±0.1 pH units, range 1 to 14 (available at nurseries/gardening stores);
  • small shovel or trowel for gathering soil samples;
  • plastic bags;
  • marking pen;
  • stick-on lables;
  • places to gather different types of soil;
  • plant pots (with drainage holes at bottom;
  • paper cups;
  • tap water.

Experimental Procedure

  1. Do your background research so that you understand the terms, concepts, and questions, above.
  2. Gather samples of different soil types. Here are some things to keep in mind:
    • For each different area or soil type, gather 10–15 small samples, and mix them together.
    • Keep each soil type in a separate plastic bag.
    • Label each of your bags.
    • Take notes in your lab notebook about the site where you collected each sample. Include information about the general area (your yard, a park, the beach, a pine forest, etc.), and the kinds of plants (if any) growing in the area.
    • Try to include as wide a variety of soil types and environments as you can.
    • For a method for determining soil type, see the Science Buddies project Get Down and Dirty: How Does Soil Change with Depth? You can use step 10 in the Experimental Procedure from that project to determine the soil texture, using a sample of soil from each site.
  3. Read the instructions for your soil pH meter to learn how to use it properly. Make sure you follow any instructions for calibrating the pH meter before using it.
  4. Use the soil pH meter to measure the pH of each soil sample.
  5. Use the soil pH meter to measure the pH of the water before it contacts the soil.
  6. Then, for each soil type, fill a plant pot about two-thirds full with soil. Try to use the same amount of soil (by weight) in each pot. (You can estimate the weight by hand, but if you have a scale that's even better.)
  7. Add enough water to the soil in the pot so that it drips out the bottom, and catch the run-off in a clean paper cup.
  8. Measure and record the pH of the run-off water.
  9. Which soils change the pH of the water the most? The least?

Variations

  • For soils with pH that is more acidic or more basic than your tap water: if you keep watering the soil sample, does the pH of water eventually stop changing? Has the pH of the soil changed? How much water did it take? Does this vary with soil type? What does this tell you about irrigation and soil pH?
  • How does the addition of fertilizer affect soil pH? Does the fertilizer type matter? Do background research on fertilizers and pH and then devise an experiment to test fertilizer-induced pH changes.
  • Use an aquarium test kit to check nitrate levels in water drained from soil pots with and without fertilizer. Be sure to check a sample of the plain tap water too, as a control. Is there less nitrate run-off when plants are growing in the pots?

Credits

Andrew Olson, Ph.D., Science Buddies

Sources

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Are There Dangerous Levels of Lead in Local Soil?

Posted by Crevolt at 10:13 AM

Objective

The purpose of this project is to determine whether local soil contains dangerous levels of lead. This is significant because the results will indicate where the soil is hazardous to the health of humans, especially young children.

Introduction

Photo

Lead is an element that has been used for centuries in many objects found in and around the home. Lead is also highly toxic to human health. In the 1980's federal, state, and local governments moved to ban the use of lead in common household materials. However, there are products that were created before the 1980's still in use today. Many areas also have soil contaminated from previous use of these products. Are there areas around you where residual products have caused the soil to be hazardous to the health of humans, especially young children?

Terms, Concepts and Questions to Start Background Research

In order to properly conduct this experiment you should become an expert on lead. You should understand:

  • What are the health effects of lead?
  • What levels of lead are hazardous?
  • When does lead become hazardous to humans?
  • How does lead get into soil?

Bibliography

General information on lead, its history, and its health hazards, and areas around your community that you might want to check for lead contamination can be found at the following websites:
http://www.epa.gov/lead/
http://www.epa.gov/lead/leadpbed.htm#Brochures
http://www.epa.gov/history/topics/perspect/lead.htm
http://www.niehs.nih.gov/external/faq/alpha-l.htm#lead

A good list of additional offline sources from Environmental Science Archive of Ask A Scientist:
http://www.newton.dep.anl.gov/newton/askasci/1995/environ/ENV134.HTM

Guidelines for soil sampling for residential property:
http://www.ecy.wa.gov/pubs/0309044.pdf
http://www.ext.colostate.edu/pubs/crops/00500.html

Materials and Equipment

  • Resealable plastic bags to hold samples
  • Shovel
  • Stainless steel spoon
  • Permanent marker
  • Large bowl or bucket
  • Paper towels

Experimental Procedure

  1. Determine your sampling locations and where, within that location, you are going to collect sub-samples. Lead concentrations can vary from one spot to another, so it is important to use a composite of sub-samples to evaluate an area rather than relying on a single sample. The exception to the composite technique would be if you are trying to get a specific measurement for a small area (for example, around a play structure).
  2. Collecting a composite sample (adapted from the Washington State Department of Ecology Arsenic and Lead Soil Sampling Guidance Brochure):
    • Sketch out a map of the location that you will be testing and note where you will be collecting each of your samples. You should collect at least 4 samples from smaller areas (for example, a small yard that is less 800 sq. ft.) and at least 15 samples from larger areas (for example, a small neighborhood park).
    • Remove material on the soil surface (grass, leaves, etc.), exposing the soil.
    • Dig a hole with your shovel. The depth will depend on the test you are using to analyze the soil—check the instructions on the home kit or with the analyzing lab to get a specific soil depth recommendation for your samples. (Typically you should not dig deeper than 6 inches).
    • Using your spoon, scrape some soil from the hole and place it in a clean plastic bag. Make sure to collect only soil—do not include rocks, grass, or wandering insects.
    • Clean the spoon with a paper towel to remove any visible traces of soil.
    • Repeat steps 2–5 for each of the sub-samples for this location.
    • Once you have collected all of the sub-samples for a location, put equal amounts of each sub-sample into your bowl and mix them together.
    • Take a sample from this composite soil mixture and put it in a new plastic bag. This is the sample that is tested.
    • Mark the plastic bag with the location name and date of collection.
    • Repeat steps 1–9 for each of your sample locations.
  3. Testing the samples: There are a number of do-it-yourself kits that test for lead available on the market. Unfortunately, according to the EPA, these kits simply test for the presence of lead, and do not provide enough distinction between high and low levels of lead (http://www.epa.gov/lead/qa4.pdf). To accurately draw conclusions from your samples, we recommend that you do the following:
    • Use a home test kit to get a positive or negative reading on the lead content of your samples. These results will give you enough information to claim that lead is present.
    • For those samples that show positive indicators for lead, do a follow up check with a soil testing laboratory. There are laboratories associated with universities (for example, University of Massachusetts [http://www.umass.edu/plsoils/soiltest/lead1.htm]) as well as commercial laboratories (see http://www.ext.colostate.edu/PUBS/crops/00520.html for a list of some).

Variations

Other toxins such as mercury

Credits

Madeleine Disner; Jordan Liu; Sarah Stegman-Wise

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Acid Rain and Aquatic Life

Posted by Crevolt at 10:12 AM

Objective

In this experiment you will test the effects of acidic water conditions on an aquatic environment containing algae, worms, snails, and plants.

Introduction

Acid rain occurs when pollution in the atmosphere (sulfur dioxide and nitrogen oxide) is chemically changed and absorbed by water droplets in clouds. When there is precipitation, the droplets fall to earth as rain, snow, or sleet. The polluting chemicals in the water droplets form an acid by combining with the hydrogen and oxygen in the water. These acidic droplets (pH <>

"Acid rain is a serious environmental problem that affects large parts of the US and Canada." (EPA, 2006) Acid rain accelerates weathering in carbonate rocks and accelerates building weathering. It also contributes to acidification of rivers, streams, and forest damage at high elevations (Wikipedia contributors, 2006).

Acid Rain

What is an acid? An acidic solution will donate hydrogen ions and usually taste sour, like lemon juice. Acids are the opposite of bases, which accept hydrogen ions and usually feel slippery, like soapy water. How do you tell if something is an acid or a base? You use a chemical called an indicator, which changes in color when it goes from an acidic to basic solution. Indicators can be extracted from plant pigments, like red cabbage. If you want to learn how to make your own acid indicator, read the Science Buddies experiment Cabbage Chemistry.

In this experiment you will use an indicator that is concentrated on little strips of paper called "pH test strips". The color of the paper will indicate the pH of the solution you are measuring. Each one unit change in pH is a 10-fold change in the number of hydrogen ions in solution. Your pH test strips will come with a color chart that you can use to measure the pH of your vinegar solutions. This will give you a measurement of the acidity of your aquatic environments.

The goal of this experiment is to test the effects of acid rain on a simple aquatic ecosystem, consisting of small plants and animals. You will use household vinegar to create different solutions of various acidities. You will then observe the organisms in the experimental environment to determine the effects of acidic conditions on viability. To measure viability, you will count the number of living and non-living organisms in each experimental environment over time.

Terms, Concepts and Questions to Start Background Research

To do this type of experiment you should know what the following terms mean. Have an adult help you search the internet, or take you to your local library to find out more!

  • acid rain
  • pH
  • environmental toxicity
  • aquatic organisms
  • aquatic environments

Questions

  • How will acidic conditions affect an aquatic ecosystem?
  • Will all of the organisms be affected similarly or differently?
  • Which pH ranges will cause an effect?

Bibliography

Materials and Equipment

  • large bottle of white vinegar
  • 3 gallons of distilled (bottled) water
  • pH test strips (Alkalive pH Stix can be found at natural food pharmacies, or you can order pH test strips from a scientific supply company like Carolina Biological)
  • measuring cups
  • 6 large, reusable plastic containers with lids (6 cups / 48 oz, e.g. Glad or Zip-lock)
  • permanent marker for labeling
  • aquatic organisms: (should pick at least 2 plants and 2 animals)
    • small, cheap fish (minnows, feeder fish, or goldfish from pet shop or bait shop)
    • small pond snails (pond or aquarium supply store)
    • water fleas (Daphnia, available at aquarium supply stores)
    • live tubifex (available at aquarium supply stores, bait shops, or found in pond bottoms)
    • aquatic plants like duckweed or elodea (available at aquarium supply stores, ponds, or nurseries)
    • algae (spirulina, available at aquarium supply stores)

Experimental Procedure

  1. Rinse each container thoroughly with water. Do not use soap because it can coat the plastic container and may be harmful to the organisms in your experiment. Label each container with a permanent marker.
  2. Prepare the solutions for each container according to the data table below, one container for each experimental group. Use bottled water, not tap water, because it may contain harmful chemicals like chlorine or chloramine:

    BowlWaterVinegarTotal Volume pHObservations
    1 1000 mL 0 mL 1000 mL
    2 900 mL 100 mL 1000 mL
    3 800 mL 200 mL 1000 mL
    4 700 mL 300 mL 1000 mL
    5 600 mL 400 mL 1000 mL
    6 500 mL 500 mL 1000 mL

  3. Check the pH of each container with your pH test strips and record the data in your data table.
  4. Evenly distribute the organisms into each container, being sure to add a mixture of plants (algae, duckweed, elodea) and animals (aquatic worms, snails, and small crustaceans). Write down the number of each type of organism you are adding to the containers. For example, "I added 10 snails,10 worms, and 20 duckweed plants to each container."
  5. Observe the animals and write down observations in the data table. Continue your observations for a few hours, or overnight if necessary.
  6. For each observation, count the number of organisms that are still alive for each different plant or animal. This is called a viability assay, because you are counting the number of things that are viable, or still living. For example, "At 3 PM there were 5 living snails, 2 living worms, and 7 living duckweed plants."
  7. Make a graph of your results. On the left side (Y-axis) of the graph, make a viability scale by graphing the number of living organisms of each type. On the bottom (X-axis) of the graph make a scale of the pH of the water. Then make a line graph for each type of organism in your study. Did they respond similarly or differently to the changes in pH of your environment? What is the viable pH range for each organism? Which organisms are the most sensitive or the most resilient to changes in acidity?

Variations

  • Another way to test the effect of acid rain on plants is to germinate seeds in acidic conditions. Try using your solutions to wet a paper towel in a baggie, sprinkle in some seeds, and place in a sunny window to see how many will sprout.
  • You can also try watering a series of plants with neutral and acidic water. How well will plants grow when watered with "acid rain" compared to neutral water?
  • Try these other Science Buddies experiments to test the effects of toxins on aquatic environments:

Credits

Sara Agee, Ph.D., Science Buddies

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Environmental Engineering Projects

Posted by Crevolt at 7:25 PM

The human population on Earth is now more than 6 billion, and still growing. With more and more of us living an energy-intensive, modern lifestyle, the environmental stresses from human activity continue to increase. Greenhouse gases leading to global warming and fertilizer run-off resulting in marine "dead zones" are just two examples of large-scale environmental impacts from human activity. For tackling big problems like these, we'll need people who can understand complex ecosystems, and who can apply that knowledge to satisfy human needs in sustainable ways—people like environmental engineers.

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