READING the RIVER

Summer 2002

PH of Water—A lesson for Grade 7 Science

Mary E. BachBath County Middle School

Bath CountyJuly 2002

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INTRODUCTION

These lessons on pH focus on three levels- 1) an understanding of pH, 2) the student’sability to conduct pH tests on water samples, 3) correlation of pH levels with otherenvironmental factors and consumers.

As part of a basic Chemistry unit in the seventh grade, there will be lessons taughtprior to this one:

1. A basic introduction to pH.

2. Draw pH scale – use a copy of pH values of common substances to relate to real world.

3. Teacher demonstration of color change, litmus paper tests, and preparation and use of purple cabbage juice indicator liquid.

4. Student lab – Testing various common items and establishing a pH scale toRange in color from the most acidic to the most basic. Students will usecabbage juice indicator solution.

In addition to the lessons above, students will have already studied an Environmentalunit earlier in the year that will have covered the following basic principles that may beapplicable in this unit as well.

1. Structure of a water molecule2. Physical properties of water3. The water cycle4. Ground water5. Erosion6. Pollution

These lessons will lead the class into a study of Acid Rain.

OBJECTIVES:

In these lessons, students will:1. Understand, explain, and correctly use the basic pH scale.

2. Test various water samples.

3. Analyze the relationship between pH level, weather conditions, and pollutants.

4. Identify the effects of pH levels of water with rainfall, water treatment, wastetreatment, and consumer satisfaction.

5. Draw conclusions about differences among various types of water.

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PROGRAM OF STUDIES

• Identify and refine questions that can be answered through scientificinvestigations combined with scientific information.

• Use appropriate equipment, tools, techniques, technology, andmathematics in scientific investigations.

• Use evidence, logic, and scientific knowledge to develop scientificexplanations.

• Communicate designs, procedures, and results of scientificinvestigations.

• Recognize how science is used to explain and answer questions.• Conduct different kinds of scientific investigations to answer different

kinds of questions.

CORE CONTENT

• Data can be interpreted and information gained and can be applied tonew situations.

• A substance has characteristic properties and predictions can be madeabout those substances based on properties.

• Questions can be answered through scientific investigations.

TEACHER BACKGROUND INFORMATION AND NOTES

1. pH measures the degree of acidity. It is a measurement of the activity ofhydrogen ions in a given sample. The pH scale is based on numbers 0-14. 0 isthe most acidic, 14 is the most basic and 7 is considered neutral.

2. Rainwater is normally 5.5-6.0 pH.

3. The pH scale is logarithmic, so every 1-unit change in pH represents a 10-foldchange in acidity.

4. Changes in water’s pH can affect aquatic life by changing aspects of water’schemistry. i.e. Toxic metals trapped in sediments are released into water at lowerpH levels.

5. A range of 6.5-8.2 pH is optimal for most organisms.

6. Rapidly growing algae removes carbon dioxide from the water duringphotosynthesis. This can result in a significant increase in pH levels.

7. Since most aquatic organisms are susceptible to changes in pH, water pH shouldbe carefully monitored.

8. Chemical testing only valid at the time of testing.

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9. Tests should be done at different locations over a period of time to identify trends,if they exist.

10. Weather conditions should be recorded at the time of the test as well as those ofthe previous 24 hours.

11. Acidic water can cause problems by dissolving lead or other metals from thepipes it goes through.

12. Hard water is water containing high levels of calcium and magnesium. Theseminerals come from rocks, such as limestone. Hard water does not form sudswell when mixed with soap. The minerals also can form deposits that can clogmachinery and pipes.

13. Soft water is water that contains lower levels of minerals calcium and magnesium.Soft water leaves fewer deposits and forms better soapsuds that hard water.

14. An ion is an atom or group of atoms that has an electric charge because it has lostor gained one or more electrons. When an acid is mixed with water, it separatesinto ions.

15. An acid is a compound that produces hydrogen ions in water.

16. A base is a substance that produces hydroxide ions in water.

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SIGNIFICANT LEVELSA range of pH 6.5 to pH 8.2 is optimal for most organisms (Fig. 3.3). Rapidlygrowing algae or SAV remove carbon dioxide (CO2) from the water duringphotosynthesis. This can result in a significant increase in pH levels.

AT pH: EFFECT ON AQUATIC LIFE:3.0-3.5 Unlikely that fish can survive for more than a few hours in this range, although

some plants and invertebrates can be found at pH levels this low.3.5-4.0 Known to be lethal to salmonids.4.0-4.5 All fish, most frogs, insects absent.4.5-5.0 Mayfly and many other insects absent. Most fish eggs will not hatch.

Bottom-dwelling bacteria (decomposers) begin to die. Leaf litter and detritusbegin to accumulate, locking up essential nutrients and interrupting chemicalcycling. Plankton begin to disappear. Snails and clams absent. Mats of fungibegin to replace bacteria in the substrate.

5.0-5.5

Metals (aluminum, lead) normally trapped in sediments are released into theacidified water in forms toxic to aquatic life.

6.0-6.5 Freshwater shrimp absent. Unlikely to be directly harmful to fish unless freecarbon dioxide is high (in excess of 100 ppm).

6.5-8.2 Optimal for most organisms.8.2-9.0 Unlikely to be directly harmful to fish, but indirect effects occur at this level

due to chemical changes in the water (see next page).9.0-10.5 Likely to be harmful to salmonids and perch if present for long periods.10.5-11.0 Rapidly lethal to salmonids. Prolonged exposure is lethal to carp, perch.11.0-11.5 Rapidly lethal to all species of fish.

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Approximate pH Values of Some Common Solutions

solution

0

1 battery acid

2 stomach acid (1.0-3.0)lemon juice (2.3)acid fog (2-3.5)

3 vinegar, wine, beer, soft drinks

4 orange juice, tomatoes

5 black coffeepH-balanced shampoo (4.0-6.0)

6 milk (6.6) saliva (6.3—7.5)

7 pure water

8 sea water (7.8-8.3)non-pH balanced shampoo

9 baking sodaphosphate detergentsantacids

10 milk of magnesia (10.5-11.9)

11 household ammonia (10.5—11.9)

12 nonphosphate detergents

13 hair remover

14 oven cleaner

pH

neutral

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VOCABULARY

1. pH SCALE - series of numbers to indicate how acidic or basic a substance is on a scale of 0-14.2. alkaline - another name for a base. pH value above 7.

3. acid - pH lower than 7.

4. neutral - pH of 7

5. indicator - a liquid that changes color in the presence of an acid or a base.

6. leaching - water and dissolved materials passing through layers of the earth.

7. runoff - precipitation that does not soak into the surface.

8. watershed - all the land area that drains into a particular stream or river.

9. groundwater - accumulated water in the ground.

10. erosion - removal of soil particles by the action of moving wind, water, or action of organisms.

11. water quality - measurement of the substances in water, including pH.

12. hardness - high levels of minerals dissolved in water.

13. softness - low levels of minerals dissolved in water.

14. filtration - process of passing water through a series of screens that allow water to pass through, but restricts solid particles.

15, flocs - sticky globs

16. coagulation - process of having clumps sink to the bottem

17. chlorination - process of adding chlorine.

18. sewage - waste materials and wastewater

19. sludge - deposits of fine solids

20 septic tank - underground tank containing bacteria that treats wastewater from homes.

21. drought - a period of scarce rainfall.

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22. pollution - addition of any substance that has a negative effect on water or the living things that depend on water.

23. ion - an atom or group of atoms that has lost or gained 1 or more electrons.

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LESSON: WHAT DO THE NUMBERS MEAN?

Problem: How does the pH of water change as it travels from source point through treatment facilities?

Skills: observing, inferring, comparison, drawing conclusions

Materials: water samples Slate Creek Tap water Sewage facility-incoming Sewage facility-completion of treatment LaMotte pH treatment kit 4 collection bottles thermometer

Procedure:1. Collect water samples from the following sites. Label each collection jar.

a. Raw, untreated water from Slate Creekb. Tap water from Owingsville treatment facility.c. Incoming liquid at sewage treatment facility.d. Water after treatment at sewage facility

2. Following the directions on pH treatment kit, test each sample.a. Fill a test tube to the 5.0 mL line with sample liquid.b. While holding dropper bottle or pipet vertically, add 10 drops of indicator

solution.c. Cap and mix.d. Insert test tube into Octet Comparator. Match color to a color standard.

3. Compare pH values and record data.

Data:

Collection Date Sample/Location pH Temperature Weather Conditions24 hrs. prior test day

Raw water

Treated water

Raw sewage

Treated sewage

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Analysis/Conclusions:

1. Which sample had the highest pH? ___________________________________

2. How did the pH of raw water compare with the pH of the treated wastewater?

3. What relationship might the weather have on pH?

4. How did the pH of the drinking water change after it was treated at the watertreatment facility?

5. Why is pH important when considering water?

6. Does there seem to be a relationship between temperature and pH?

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Lesson: WATER YOU CHOOSE?

Problem: How do different waters differ from tap water?

Skills: observing, inferring, drawing conclusions, comparisons

Materials: LaMotte water test kit Purple cabbage liquid indicator liquid. Water samples Tap water Mineral water Distilled water Spring water Tonic water Small paper cups (5 per person) Test tubes – 10 Test tube rack

Procedure:1. Obtain sample bottles of tap water, spring water, mineral water, distilled water,

and tonic water.2. From the original bottles, pour a small amount of each water into labeled cups.

Taste each sample. Describe the taste of each using words like : bitter, metallic,tasteless, etc. Record data . ( CAUTION: Use a clean cup for each sample anddiscard each cup after use.)

3. Carry out pH tests on each sample of waterINDICATOR

A. Place equal amounts of test water and indicator liquid into a test tube.B. Repeat for each water sample.C. Arrange test tubes in order from most acidic to most basic.D. Estimate and assign a pH value for each water sample.

LaMOTTE pH TESTA. Conduct a pH test on each water sample.Fill a test tube to the 5.0

ML line with sample liquid.B. While holding dropper bottle or pipet vertically, add 10 drops of indicator

Solution.C. Cap and mixD. Insert test tube into Octet Comparator. Match color to a color standard.E. Assign pH values to each water samples. Record data.

EXTENSIONS;1. Into clean test tubes, add 2 drops of a liquid soap to 10 mL of each of the

different water samples.2. Place a stopper into each test tube sample and shake 30 times.

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3. With a ruler, measure the height of the soapsuds in the test tubes.

Data:

Water Sample Cabbage Indicator(color streak)

LaMotte kit pH

Taste Extension?Soap Ht.

(mm)

Analysis/Conclusions:

1. Which water sample would you want to drink and why?

2. What similarities did you find in your water samples?

3. What differences did you find in your water samples?

4. What other information, besides pH, might you need to know before decidingwhich water to drink regularly?

5. What factors affect the taste of water?

6. Why do you think people buy bottled water?

7. EXTENSION : Rank your water samples from the one with the fewest soapsudsto the one with the most. What relationship do you think there is betweenhardness of water and pH?

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ASSESSMENTS:

1. Lab Work, Lab analysis and conclusions.

2. Vocabulary matching test.

3. Vocabulary Seek and Find Practice

4. Group Activity Assessment and Oral Presentations.

FIELD TRIP OPPORTUNITIES

1. Visit local treatment facility

2. Visit local Waste Treatment Facility

3. Guest speaker on Water Quality

GROUP ASSESSMENT ACTIVITY

As a group, you are to conduct pH tests and compare 3 local water resources. Identifyany potential pollution problems that contribute to high or low pH and design a viableplan to correct them. This plan must include evidence of your understanding of water pH, contributingenvironmental factors, testing procedures, and acceptable reporting methods. Include allrelevant data, charts, observations, testing procedures, and suggestions for clean watersupplies. Final plan will include a written presentation, including procedure and data, as well asan oral presentation to the class with any appropriate visual aids that you choose.

GROUP ASSESSMENT RUBRIC

Master Environmental Chemistq (10 points each)

q Tests and identifies location of 3 or more local water resources.q Analyzes and or identifies 3 or more potential pollutant problems at each siteq Report includes a logical plan to correct any potential problems at all 3 sitesq Report contains evidence of knowledge of pH and acceptable testing methodsq Report includes data charts, procedures, and observationsq Oral presentation was excellent with visual aids-all members participated.

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Internq (8 points each)

q Conducts pH tests on 3 water resources.q Analyzes and Identifies 2 potential pollutant problems at each siteq Report includes a plan to correct potential problems at 2 sitesq Report shows some knowledge of pH , however testing methods lack

completenessq Report includes some data, some procedure is present, some observations

are presentq Oral presentation made, some visual aids are used, most members

participate

Apprenticeq (6points each)

q Conducts pH test on 2 local water resourcesq Analyzes and identifies 1 potential pollutant problem at each siteq Report includes correction for possible pollutant at 1 siteq Report shows pH was testedq Report includes some data and procedure is present, but flawedq Oral presentation made by at least 2 members of group

Impending Droughtq (4points each)

q Conducts pH test on 1 local water resourceq Identifies 1 potential pollutant problem at the site testedq Report mentions correction for problems-not necessarily logicalq Report mentions pHq Report has some data-procedures, if present, is weakq Oral presentation is made by at least 1 member with no visual aids

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VOCABULARY QUIZ Match the following words with their correct definitions. Place the letter of thecorrect definition in the blank space in front of the word. THINK !

__________ 1. Acid A. Another name for a base. pH value above 7.

__________ 2. Alkaline B. series of numbers to indicate how acidic or basic a substance is on a scale of 0-14.

__________ 3. Chlorination C. pH of 7.

__________ 4. Coagulation D. a liquid that changes color in the presence of an acid or base.__________ 5. Drought E. water and dissolved materials passing through layers of the earth.__________ 6. Erosion F. precipitation that does not soak into the

surface.

__________ 7. Filtration G. All the land area that drains into a stream or river.__________ 8. Flocs H. Accumulated water in the ground

__________ 9. Groundwater I. Removal of soil particles by the action of moving wind, water, or action of organisms.]__________10. Hardness J. measurement of the substances in water,

including pH.

__________11. Indicator K. high levels of minerals dissolved in water.

__________12. Ion L. low levels of minerals dissolved in water.

__________13. Leaching M. process of passing water through a series of screens that allow water to pass through, but restricts solid particles.__________14. Neutral N. sticky globs.

__________15. pH scale O. process of having clumps sink to the Bottom.__________16. Pollution P. process of adding chlorine

__________17. Runoff Q. waste materials and wastewater.

__________18. Septic tank R. deposits of fine solids

__________19. Sewage S. Underground tank containing bacteria that treats wastewater from homes.__________20. Sludge T. A period of scarce rainfall

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__________21. Softness U. Addition of any substance that has a negative effect on water or the living things that depend on water.__________22. Water Quality W. an atom or group of atoms that has lost

or gained 1 or more electrons.

__________23. Watershed X. pH lower than 7.

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EXTENSION ACTIVITIES FOR pH LESSONS

1. Create a scenario giving each student 100 gallons of water within the acceptablepH range to last for a 5 day period. Students are to describe how they wouldadapt and how they would use the 100 gllons and no more. This writing could bedeveloped into a portfolio piece. To complete this activity, students would needto deep a water diary over a 5 day period, develop a data chart to show useage,and compare the reality figures with the make-believe use scenario.

2. Students will design and experiment to find out what happens to the pH levels ofWater and soil as acid rain percolates through different depths of soil.

3. Do chalk/acid rain lab (see attached)

4. Visit local cemetery with monuments of varying ages and examine marbleMonuments, recording their conditions. Devise a scale for recording observationsand data.

5. Research and prepare a chart that shows positive/negative aspects of high andLow pH values of water. Include steps we can follow to decrease/increase pHvalues of water.

6. Test dissolved oxygen. Dissolved oxygen is a good water quality indicator.Design an investigation that explores the relationship between dissolved oxygenand pH.

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BIBLIOGRAPHY

Lester, James; Shelton, Jane; Smith, Gary, Water We Gonna Do?, Kentucky Prism Unit.

Roa, Michael L, Environmental Science Activities Kit, The Center for Applied Research in Education, 1993.

Science Explorer, Earth’s Waters, Prentice Hall, 2002

The Monitor’s Handbook, LaMotte, Campbell, Gayla; Wildberger, Steve, 2001 p. 33-34.

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