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Activity Guide
Troubled Waters: Grab a Gram

IDEAS FOR THE INFORMAL SETTING

  • Part II and Part III may be instructor led.
  • Display common items/solutions of various weights and concentrations.

OVERVIEW

Students use familiar materials to gain an introduction to basic water quality measurement like parts per million (ppm) and milligrams per liter (mg/L). Students compare these measurements to national drinking water standards to determine toxicity levels of a contaminant.

(Note: National reforms in teaching the metric system call for students to use the metric system exclusively, without converting from the English system. This practice is applied in this activity. If conversions from English units to metric are needed, please search the Internet for conversion calculators). www.sciencemadesimple.com/conversions.html

OBJECTIVES

Students will:

  • Determine whether drinking water contaminants are always visible.
  • Use common objects to determine the relative size and weight of one gram (g), one milligram (mg), and one microgram (µg).
  • Calculate metric conversions from common water quality measurements.
  • Describe the relationship between common units of water quality measurement — mg/L, ppm, ppb.
  • Compare common water contaminant measurements with maximum allowable levels.

SUBJECTS

Chemistry, Environmental Science, Earth Science, Life Science, Health Science, Social Studies, Mathematics, Metrics

VOCABULARY

Atrazine, concentration (of a solution), consumer, fertilizer, contaminant, drinking water standards, toxicity

TIME

Preparation: 30 minutes
Activity: 50 minutes

MATERIALS

  • Items that weigh about one gram (sugar packet, raisin, paper clip, etc.)
  • Items that weigh more and less than one gram (staple, clothespin, pen, etc.)
  • One liter bottle filled with water (one per group) (Optional: only one bottle needed if conducted as a demonstration)
  • Approximately one kilogram (2.2 pounds) of sand, sugar, or salt (one per group) (Optional: only one kilogram needed if conducted as a demonstration)
  • Business card with at least 25 tiny pieces cut out of it (Optional: business card cut into 1000 equal pieces)
  • Copies of handouts: Water Quality Measurement Worksheet (one per student) and Comparison of International Drinking Water Guidelines (one per student)

NATIONAL SCIENCE EDUCATION STANDARDS

This activity supports the following National Academy of Sciences Science Education Standards (Grades 5-8):

  • Unifying Concepts and Processes—Constancy, change, and measurement
  • Standard A: Science as Inquiry—Abilities necessary to do scientific inquiry
  • Standard A: Science as Inquiry—Understandings about scientific inquiry

BACKGROUND

The effort to keep clean, healthy, drinkable water dates back to the Roman Empire when it was illegal to dump garbage in cisterns or to place a furnace, tannery, slaughterhouse, or cemetery within 25 meters of a well. Today, US cities and towns have drinking water treatment plants that monitor water quality daily. Every drinking water treatment plant produces an annual Consumer Confidence Report (CCR) which documents the average measured levels of each contaminant — chemicals, metals, or other substances that pollute water. CCRs are available to all consumers and are often printed in local newspapers and on the Internet at www.waterhistory.org .

Contaminants are measured to ensure that their concentrations — the mass of chemical per unit volume of water — do not exceed the Maximum Contamination Level (MCL) established by the US Environmental Protection Agency (USEPA). It is important to monitor these contaminants because in parts of the country certain contaminants have caused health problems when they exceeded the MCL. Concentrations of contaminants can vary widely, and some are simply far more harmful, or toxic, than others, even at very low concentrations (e.g., arsenic, lead, mercury, cyanide). Some contaminants that pose less risk to human health are called secondary MCLs. These include iron, fluoride, and aluminum. Though secondary MCLs are not federally regulated, many are regulated by state laws.

Most water quality measurements are recorded in milligrams per liter (mg/l), or the number of milligrams of a contaminant that are present in one liter of water. One milligram per liter (mg/l) is equal to one part per million (ppm) because one liter of water weighs 1000 grams and one milligram is one one-thousandth of a gram. Therefore, there are 1,000,000 milligrams in one liter of water, and each of those milligrams equals one part per million.

Even smaller in concentration, a microgram per liter of water is one one-thousandth of a milligram per liter, and can be expressed as micrograms per liter, or µg/L. It is also equivalent to one part per billion (ppb). One ppb is 1,000 times a part per million.

Concentrations measured in ppm and ppb are so small that they can be difficult to conceptualize. Try these relative concentrations to help your students visualize them.

  • One part per million is equal to one minute in two years.
  • One part per billion is equal to one minute in 2000 years.

(Water on the Web, 2001)

BEFORE YOU BEGIN

1. Make one copy per student of the Water Quality Measurement Worksheet and the Comparison of International Drinking Water Guidelines .

2. Cut 25 tiny pieces from a business card.

WHAT TO DO

Warm up:

1. Show students a glass of clear water. Ask them if there are chemical or biological contaminants in the water even if they cannot see them. If students maintain that there may be contaminants in the water that they cannot see, ask them how to determine if there are contaminants in the water. Make a list of their answers.

2. After all answers are given, explain that water can be tested to determine if contaminants are present. These tests involve measurements of very small amounts of contaminant. The most common unit of measurement in such a case is milligrams per (mg/l). Inform students that they will investigate common water quality measurements in this activity.

Part I:

1. Ask students to think about and predict the weight of several objects in the classroom. Have students record their predictions. If a scale is available, record the weight in metric units and compare them to students’ predictions. (Some metal folding chairs weigh about 4½ kilograms. A new wooden pencil weighs about seven grams.)

2. Knowing that a pencil weighs about seven grams, students should name other classroom objects that weigh about one gram.

3. Pass around a tray of items, including some that weigh about the same as, more than, and less than one gram. Have students try to select the items that weigh about one gram.

Part II:

1. Divide students into small groups and distribute a copy of the Water Quality Measurement Worksheet to each student.

2. Provide each group with a one liter bottle and have them fill it with water.

3. Have students drop an object weighing one gram (e.g., small paper clip, raisin, etc.) into their liter of water. Ask students what measurement or concentration results from this action. (Answer: one gram in a liter of water, or 1 g/l). Have them record their answer on their worksheet.

4. Have students examine their one gram object, and imagine it sliced into 1,000 pieces. Prior to this step, cut 25 tiny pieces from a business card (business card weighs approximately one gram), telling the students that you were “up all night painstakingly cutting a business card into 1,000 equal pieces.” Distribute a few tiny specks of paper to each group, informing them as you do, that each speck represents one-thousandth of the original one gram object.

5. Ask students what measurement each of the tiny specks of paper represents. (Answer: one-thousandth of a gram, or 1 mg). Have students record their answers on their worksheet.

6. Have students drop one of the specks into the liter of water. What concentration or measurement results? (Answer: one milligram per liter of water, or 1 mg/l). Ask students to record their answers on their worksheet.

Part III:

1. Divide the class into small groups and explain that 1 mg/L can also be expressed as one part per million. The following activity will demonstrate this concept.

2. Explain the following conversions to the students. One mg/l of water is equivalent to 1 ppm because a liter of water weighs 1000 grams and a milligram is one one-thousandth of a gram. You may notice students struggling to understand these conversions, so explain that they will now be able to demonstrate this concept for themselves.

3. Give each group one kilogram of sand, sugar, or salt in a container or in a pile. If you do not have a scale, use a little less than half of a five-pound bag (common size) of salt or sugar.

4. Inform the students that the substance weighs one kilogram and ask them to suppose that there are 1 million grains of the substance in the pile.

5. Instruct students to complete their worksheets for Part III.

UPPER-LEVEL OPTION

  • Distribute the Comparison of International Drinking Water Guidelines chart to each group. Have each group complete the questions with the assumption that their liter of water contains 1 mg/l (1ppm) of substance.

WRAP UP

Review with the students the answers on the worksheets (Answers: Water Quality Measurement Work sheet , Part II: 1. 1g/L; 2. 1 mg; 3. 1 mg/L, Part III: 1. 1; 2. 1 ppm or 1 mg/l)

Were students able to successfully identify the correct measurements? Have students individually write out the list of measurements and conversions between concentrations (from kg to units u; from g/l to units u/l; from ppm to ppb).

Challenge students to create an analogy to describe one of the measurements from the activity (e.g., One part per million is equal to one minute in two years.) Share these analogies with the class.

Upper Level Wrap Up: Have students discuss the differences in the allowable concentrations of arsenic, copper, nitrates, and sulfates in drinking water. What relationships exist between the concentration of a drinking water contaminant and the toxicity of the contaminant (risk to human health)?

ASSESSMENT

Have students:

  • determine whether drinking water contaminants are always visible and apparent. (Warm Up)
  • complete the worksheet provided (Part I, Part II, Part III)
  • use common objects to determine the relative size and weight of one gram, one milligram, and 1 microgram (Part I, Part II, Part III).
  • calculate metric conversions related to common water quality measurements (Part II, Part III).
  • describe the relationship between common water quality measurement units—mg/l, ppm, ppb (Part II, Part III).
  • compare measurements of common water quality contaminants with allowable maximum contaminant levels of those contaminants (Upper-Level Option).

Needs improvement—Student fails to answer or answers incorrectly more than half of the worksheet questions. Student cannot provide at least one example or calculation per assessment question.

Satisfactory-—Student correctly completes at least two-thirds of the worksheet questions and provides at least one example or calculation per assessment question.

Excellent—Students correctly completes the worksheet questions, provides at least one example or calculation per assessment question. Student creates an analogy to describe one of the measurements from the activity.

EXTENSIONS

  • Have students investigate their own city or town’s drinking water quality by obtaining a local Consumer Confidence Report (CCR). Once obtained, compare the average local contaminant level with the Maximum Contaminant Level (MCL) for the contaminants studied in this activity.
  • Have students research the different measurements used for nitrates in the Comparison of International Drinking Water Guidelines chart. What is the difference between 10.0 mg/l as N and 50 mg/l as NO3?
  • Search the Web sites that contain Consumer Confidence Reports for your town or for the closest large city. Investigate any other pertinent information about measurement of water quality contaminant levels. Visit the USEPA Web sites for a complete list of MCLs in the US
  • Have students visit Water on the Web at www.nrri.umn.edu/wow/under/units.html
  • Challenge students to find different ways of expressing ppm and ppb using rations of common items.
  • Use Healthy Water, Healthy People Testing Kits, which include all materials and equipment needed for field and classroom analysis of water samples for chemical, physical, and biological parameters. Healthy Water, Healthy People Testing Kits are available for a variety of parameters, grade levels, skills, and prices. Each Healthy Water, Healthy People testing kit package includes the Water Quality Educators Guide, a testing kit, the Healthy Water, Healthy People Testing Kit Manual containing detailed background information, testing kit activities, and a case study for each parameter. www.healthywater.org/testingkits.html

MORE INFORMATION

Water on the Web. 2005. Advanced technologies and real-time data in basic and water science waterontheweb.org/

Books, Articles, and Videos

  • Barzilay, J.I. et al. The Water We Drink: Water Quality and its Effects on Health. Piscataway: NJ Rutgers University Press, 1999.
  • Water Analysis Handbook. Loveland: Hach Company, 1997.
  • Harte, J. et al. Toxics A to Z: A Guide to Everyday Pollution
  • Hazards. Berkeley: University of California Press,1991

CREDIT

From Healthy Water, Healthy People Water Quality Educators Guide. For more information, visit www.healthywater.org or call 866-337-5486 (toll free).

CONVERSIONS REFERRED TO IN THIS ACTIVITY:

  • 1 kilogram (kg) = 1000 grams (g)
  • 1 gram (g) = 1000 milligrams (mg)
  • 1 kilogram (kg) = 1 million milligrams (mg)
  • 1 kilogram (kg) = 1 billion micrograms (µg)
  • 1 milligram (mg) = 1000 micrograms (µg)

Concentrations:

  • 1 gram/L = 1 part per thousand (ppt)
  • 1 milligram/L = 1 part per million (ppm)
  • 1 microgram/L = 1 part per billion (ppb)

WEIGHT IN GRAMS OF COMMON ITEMS

Thin rubber band = .16
Thick rubber band = .45
Small paper clip = .46
Plastic head thumb tack = .47
AltoidTM candy = .79
Business card = 1.0
Large paper clip = 1.2
EqualTM packet = 1.2
Sweet and Low packet = 1.3
Dime = 2.3
Penny = 3.0
Sugar packet = 3.1
Wooden pencil unsharpened = 6.9


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