Principal Developer of So Fresh, So Clean
Nicholas Hoffmann, MAT
Additional Contributors to So Fresh, So Clean
Polly Dornette, MEd, MS
Crystal Harden, MAT
Cathy Pike, MEd
Amber Vogel, PhD
Laura Walters, BA
Ru Yuan, BA
Our Thanks Go to the Following
and Sewer Authority
Jamila Bowser and her students at Lowe’s Grove Middle School,
Durham, North Carolina
The DREAMS (DESTINY’s Role in Expanding and Advancing Middle School Science) Initiative provides equity of
access to innovative science education technology and experiences for the middle school students of North Carolina
and engages in informing 7th- and 8th-grade science teachers of best practices for science education through the DESTINY curriculum modules and traveling science laboratories.
The DESTINY Traveling Science Learning Program is a science education outreach initiative of Morehead Planetarium and Science Center at UNC-Chapel Hill that serves pre-college teachers and schools across North Carolina.
DESTINY develops and delivers a standards-based, hands-on curriculum and teacher professional development with
DESTINY has been supported in part by the State of North Carolina; grants from GlaxoSmithKline, the Howard
Hughes Medical Institute, and the National Aeronautics and Space Administration; and a Science Education Partnership Award from the National Center of Research Resources, part of the National Institutes of Health. Additional support has come from Bio-Rad, IBM, Medtronic, and New England BioLabs.
© 2009 The University of North Carolina at Chapel Hill, through its Morehead Planetarium and Science Center. The
University of North Carolina at Chapel Hill grants teachers permission to reproduce materials from this curriculum
guide for classroom use only, without alteration, provided all copies contain the following statement: “© The University of North Carolina at Chapel Hill, through its Morehead Planetarium and Science Center. This work is reproduced
solely for classroom use with the permission of The University of North Carolina at Chapel Hill, through its Morehead
Planetarium and Science Center. No other use is permitted without the express prior written permission of Morehead
Planetarium and Science Center of The University of North Carolina at Chapel Hill. To request permission, contact
The DESTINY Program (Morehead Planetarium and Science Center’s outreach initiative at UNC-Chapel Hill), CB#
7448, Morehead Planetarium and Science Center Annex, UNC-Chapel Hill, Chapel Hill, NC 27599-7448.”
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1
2
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5"#-&0'$0/5&/54
KEY TERMS .......................................................... 5
Wet-Lab Procedure ................................................ 37
Data Collection Sheet ............................................38
ALIGNMENTS ......................................................7
KEY Data Collection Sheet ....................................39
The Key Components of the 5E Model ................... 7
North Carolina Standard Course of Study:
8th Grade.................................................................. 8
Correlation to National Science Education
Content Standards ..................................................14
INTRODUCTION................................................15
ADDITIONAL ACTIVITIES ............................. 41
Pre-lab Explanation Activity: Dissociation
and Ions ..................................................................42
Wet-lab Engagement Activity: Simulating
Dissociation............................................................ 43
Wet-lab Activity: Wastewater Filtration.................45
Water ......................................................................15
Acids and Bases ..................................................... 15
pH...........................................................................16
Pre-Lab Activities .................................................. 16
Wet-Lab Activities .................................................16
Additional Activities ..............................................16
PRE-LAB ..............................................................17
Engagement Activity: The Price Is Nice ................18
“The Price Is Nice” Activity Sheet ........................ 19
Everyday Liquid Price Comparison Table ............. 21
“The Price Is Nice” Cards ...................................... 22
Exploration Activity: Isn’t It All Just Water? ......... 23
Bottled Water vs. Tap Water Data Cards ................24
Explanation Activity: Acids, Bases, and pH .......... 27
pH Scale Diagram (with labels) ............................. 28
Dissociation Diagram.............................................29
Elaboration Activity: Everyday Liquids ................30
pH Scale Diagram (without labels) ........................31
Evaluation Activity: Informing the Public .............32
“Informing the Public” Activity Sheet .................. 33
WET-LAB .............................................................35
Wet-Lab Engagement Activity: Indicators............. 36
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KEY TERMS
acid
An acid is a chemical compound that has at least
one hydrogen ion (H+) that it can donate to another
compound. This ability makes the acid highly reactive.
acidic
An acidic compound has a pH lower than 7.0.
acidity
Acidity is the property of being acidic, measured by pH.
consists of all atoms that have 1 proton; the element
helium consists of all atoms that have 2 protons.
EPA
The Environmental Protection Agency is the federal
agency that monitors environmental science,
environmental education, and assesses environmental
safety. This includes the establishment and monitoring
of standards for treatment of public water supplies.
alkalinity
Alkalinity is similar to basicity; it generally refers to the
ability of a compound to act as a base; however, it is not
as comprehensive as the term “basicity.”
FDA
The Food and Drug Administration is the federal
agency that monitors the safety of drugs, medical
equipment, food, and other products. This includes the
regulation of standards for bottled water.
anion
An anion is an atom or molecule that has a negative
charge.
Filtration is the process by which solid matter is taken
out of a liquid solution by passing the solution through
base
A base is a chemical compound that is able to accept
hydrogen ions, making them highly reactive as well.
).
basic
A basic compound has a pH higher than 7.0.
basicity
Basicity is the property of being basic, measured by pH.
cation
A cation is an atom or molecule that has a positive
charge.
capability to remove different amounts and sizes of
hydrogen
Hydrogen is the element whose atoms only possess a
single proton and electron.
hydrogen ion
A hydrogen ion is formed when a hydrogen atom
loses its electron, and is represented as H+. Because
hydrogen has only a single proton and single electron,
the hydrogen ion is often just referred to a proton
hydrogen ion.
dissociation
Dissociation is a chemical reaction or process that splits
a molecule into two or more of its parts. In the case of
+
water, H2
.
electron
An electron is the atomic particle with a single negative
charge.
element
An element is a group of atoms that have the same
number of protons. For example, the element hydrogen
hydronium ion
Hydronium is the ion formed when a hydrogen ion
bonds to a water molecule, represented as H3 +.
Hydrogen ions from dissociated water molecules react
quickly in aqueous solution to form hydronium ions.
hydroxide ion
A hydroxide ion is composed of one oxygen atom and
. When a
water molecule dissociates, it creates one hydroxide ion
and one hydrogen ion.
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indicator
An acid-base indicator is a compound that shows a
change in color depending on the pH of a solution.
ion
Ions are atoms or molecules that have a negative or
positive charge. This charge is caused by an imbalance
in the ratio of protons or electrons in the atom or
molecule.
neutral
A compound is neutral if it has a pH of 7.0. Water is a
neutral compound.
neutralization
Neutralization is a process or chemical reaction
in which an acid and a base react with each other,
producing water and an additional compound. This
reaction combines the H+
from the base, into neutral water.
oxygen
and 8 electrons. If an oxygen atom gains 2 electrons,
-2
. The oxygen atom in a water
-2
ion.
6
pH
pH is a measurement of how acidic or basic a solution
is. pH can be calculated by taking the negative of the
decimal logarithm of the activity of hydrogen ions in
the solution.
potability
Potability is the quality of water to affect human health
when drunk. Potable water is safe to drink, causing no
harmful health effects.
proton
Protons are the atomic particle with a single positive
charge.
volume
Volume is the measure of the space that an object
occupies. It is commonly used to measure the amount
of a liquid sold.
water
Water is a common chemical substance made of two
hydrogen atoms and one oxygen atom—H2
required for all known forms of life.
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THE 5E’s
EVALUATE
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THE 5E’s
THE 5E’s
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Competency Goal 1:
Objectives
1.02 Develop appropriate experimental procedures for:
Given questions.
Student generated questions.
1.05 Analyze evidence to:
1.07 Prepare models and/or computer simulations to:
1.08 Use oral and written language to:
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1.09 Use technologies and information systems to:
Competency Goal 2:
The learner will demonstrate an understanding of technological design
Objectives
2.02 Use information systems to:
2.03 Evaluate technological designs for:
2.04 Apply tenets of technological design to make informed consumer decisions about:
Competency Goal 3:
The learner will conduct investigations and utilize appropriate technologies and information systems to
Objectives
3.01 Analyze the unique properties of water including:
3.02 Explain the structure of the hydrosphere including:
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9
3.03 Evaluate evidence that Earth’s oceans are a reservoir of nutrients, minerals, dissolved gases, and life forms:
3.04 Describe how terrestrial and aquatic food webs are interconnected.
3.05 Analyze hydrospheric data over time to predict the health of a water system including:
3.06 Evaluate technologies and information systems used to monitor the hydrosphere.
3.07 Describe how humans affect the quality of water:
3.08 Recognize that the good health of environments and organisms requires:
Competency Goal 4
The learner will conduct investigations and utilize technology and information systems to build
Objectives
4.01 Understand that both naturally occurring and synthetic substances are chemicals.
4.02 Evaluate evidence that elements combine in a multitude of ways to produce compounds that account for all living and nonliving substances.
4.03 Explain how the periodic table is a model for:
4.04 Describe the suitability of materials for use in technological design:
10
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4.05 Identify substances based on characteristic physical properties:
4.06 Describe and measure quantities related to chemical/physical changes within a system:
4.07 Identify evidence supporting the law of conservation of matter.
products.
4.08 Identify evidence that some chemicals may contribute to human health conditions including:
4.09 Describe factors that determine the effects a chemical has on a living organism including:
Crop yield.
Sanitation.
Competency Goal 5:
The learner will conduct investigations and utilize appropriate technologies and information systems to
Objectives
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11
5.01 Interpret ways in which rocks, fossils, and ice cores record Earth’s geologic history and the evolution of life
including:
5.02 Correlate evolutionary theories and processes:
5.04 Analyze satellite imagery as a method to monitor Earth from space:
5.05 Use maps, ground truthing and remote sensing to make predictions regarding:
Competency Goal 6:
The learner will conduct investigations, use models, simulations, and appropriate technologies and infor-
Objectives
6.01 Describe cell theory:
6.02 Analyze structures, functions, and processes within animal cells for:
6.03 Compare life functions of protists:
12
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6.04 Conclude that animal cells carry on complex chemical processes to balance the needs of the organism.
Competency Goal 7:
The learner will conduct investigations, use models, simulations, and appropriate technologies and infor-
Objectives
7.01 Compare and contrast microbes:
7.02 Describe diseases caused by microscopic biological hazards including:
7.03 Analyze data to determine trends or patterns to determine how an infectious disease may spread including:
7.04 Evaluate the human attempt to reduce the risk of and treatments for microbial infections including:
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Science as Inquiry — Levels 5-8
Pre-lab Activities
1. Abilities necessary to do scientific inquiry
2. Understanding about scientific inquiry
Earth and Space Science — Levels 5-8
Pre-lab Activities
1. Structure of the earth system
2. Earth’s history
3. Earth in the solar system
Physical Science — Levels 5-8
Pre-lab and Wet-lab
Activities
1. Properties and changes of properties in matter
2. Motions and forces
3. Transfer of energy
Science and Technology — Levels 5-8
Pre-lab and Wet-lab
Activities
1. Abilities of technological design
2. Understanding about science and technology
Science in Personal and Social Perspectives — Levels 5-8
Pre-lab and Wet-lab
Activities
1. Personal health
2. Populations, resources, and environments
3. Natural hazards
4. Risks and benefits
5. Science and technology in society
History and Nature of Science — Levels 5-8
Pre-lab and Wet-lab
Activities
1. Science as a human endeavor
2. Nature of scientific knowledge
3. Historical perspectives
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T
his DREAMS curriculum module gives students
the opportunity to discover the science behind
of humans on our water supply. In particular, So Fresh,
So Clean explores the reasons that humans place value
on water and other important liquids, and how the
chemistry of a liquid affects its potability.
Studying the liquids that students encounter every day
is an excellent way to provide a link between learners’
questions:
towards these daily requirements.
Water is becoming a more and more valuable resource
because of its importance to human health and our
rapidly increasing population. As a result. water
management around the world is becoming an
increasingly sensitive issue. Worldwide, more than 1
billion people lack access to clean water. In developing
countries, more than 2 million people a year die from
water-related problems.
Amid this water management crisis, the bottled water
industry is thriving. Bottled water has become a
controversial issue for environmentalists in the United
States for a number of reasons:
Why are different sources of water more
expensive? Why does bottled water cost so much
more than tap water? What are the comparable
costs for other liquids?
Although the Food and Drug Administration
regulates bottled water standards, bottled water is
held to a lower level of standards than is tap water.
How do we know if water is safe to drink?
About 25% of bottled water is tap water that has
What are acidity and pH? How is pH measured?
Bottled water can cost thousands of times the price
of the same amount of tap water.
WATER
The transport of bottled water around the United
States uses 18 billion gallons of oil per year.
Water is the chemical compound that is most
Less than one quarter of all water bottles are
recycled, resulting in over 7 million discarded
Not only does water make up more than half of the
human body, but it also covers more than half of our
planet.
The covalent chemical bonds that connect two
hydrogen molecules to the single oxygen molecule give
water a very stable structure. While the gaseous (steam)
and solid (ice) forms of water have great importance
to society and the environment, liquid water has the
greatest impact on the living organisms of the world.
The human body needs and uses water, an essential
component of life. Each day, the human body loses
water through breath, sweat, urine, and bowel
movements. An adult produces about 1.5 liters of urine
a day, and loses another liter through the other methods
listed above. The Institute of Medicine advises males
to consume about 3 liters of water a day to make up
for this loss; they advise at least 2.2 liters of water
for females. Water is the major component of almost
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In any water-based (aqueous) solution, the individual
molecules of water will break apart, or dissociate, to
produce H+
ions. When the number of H+
ions, the ions balance
each other out to create a neutral solution. Because
both H+
ions react differently with other
compounds, solutions with different amounts of the ions
+
-
Acids and bases also
from combining vinegar (an acid) with baking soda (a
base). In combination, these two chemicals produce
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Vinegar is acetic acid.
The acid that digests food
in your stomach is called
hydrochloric acid.
The pain from an ant bite
comes from formic acid.
Vitamin C is also known as
ascorbic acid.
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Baking soda is a base called
sodium bicarbonate.
A common medication for
constipation is “Milk of
magnesia”, also known as
magnesium hydroxide.
Many strong cleaners (oven
cleaner, Drano) include a base
called sodium hydroxide.
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Combining vinegar and
baking soda results in the
famous “science fair volcano”
reaction!
Many antacids uses to help
with an upset stomach cause
a reaction. Bases like Milk
of Magnesia and sodium
bicarbonate react with excess
hydrochloric acid in the
stomach.
The sour taste in lemons and
limes comes from citric acid.
bubbles, which are often used to create the “lava” in
many science fair volcanoes. A similar reaction occurs
when you take an antacid to neutralize the acid in your
and tap water as having very different prices. Students
hypothesize reasons behind this difference, carry out
research, and then reevaluate their hypotheses.
and acid/base reactions.)
The teacher will also focus the students’ attention on the
process of water treatment. As the teacher explains the
properties of acids and bases, students will investigate
the pH of everyday liquids to construct their own pH
scales.
Q)
Scientists studying the properties of acids and bases
in the early 1900s created a simple notation system
that was capable of showing the spectrum of acidity
to basicity. You might also see basicity referred to as
alkalinity
the negative logarithm of the concentration of H+ ions.
This creates a scale of measurements between 0 and 14
that measure extreme acidity to extreme basicity.
Because of the logarithmic nature of the pH scale, the
difference in the concentration of H+ ions in a solution
with a pH of 6 versus the concentration of a solution
with a pH of 7 is 10 fold. So a 1-liter solution with a
pH of 2 has 1 million times more H+ ions than a 1-liter
solution with a pH of 8!
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Students become contestants on a game show and need
to determine the values of different liquids to win the
prize. As students compare different volumes and
prices, they discover the unexpectedly high or low
prices of some liquids. Students focus on bottled water
16
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Students learn more about different indicators and alter
a liquid’s pH to observe the indicator’s change in color.
Students will reduce the pH of untreated water to a
strongly acidic level, and then raise it up to a slightly
basic level. They will monitor the pH through the lab
using pH indicators. The wet lab simulates part of
the process of water treatment as it is done at a water
treatment plant.
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nature of water, acids, and bases. In an explanation
activity, students simulate the dissociation process. In
an engagement activity, students simulate the change
in a liquid’s pH as hydrogen and hydroxide ions are
added to it, modeling the process that the students will
perform in the wet-lab.
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Explore
Isn’t It All Just Water?
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Explain
Acidity and pH
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Elaborate
Everyday Liquids Are
Acids and Bases
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Evaluate
Scientists Inform the
Public
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Students will act as game show contestants in this activity. Around the classroom are several common household liquids. As contestants on “The Price Is Nice,”
contestants must assess how much they would pay for a
gallon of that liquid.
Because many household liquids are sold not by the
gallon, but rather by ounces, contestants will have to
convert volumes. After the contestants have recorded
their guesses, they must calculate the true cost of
each liquid. Each liquid’s “Price Is Nice” card will be
opened, and contestants can record the cost per containof each liquid. The contestant whose original assessment is closest to the true cost wins!
Bottled water and tap water are included in the household liquids, and students notice the large difference in
price between them.
."5&3*"-4
A one gallon jug full of tap water
A small bottle of bottled water
Three other liquids in their original containers.
Milk and gasoline provide interesting discussion
afterwards. If using gasoline, represent it with an
empty gas can. It is ideal to use liquids with which
the students have some familiarity.
“The Price Is Nice” cards for liquids. Write in the
name of each liquid on the front; write the current
price on the underside.
“The Price Is Nice” worksheet for students
“Everyday Liquid Price Comparison” for reference
how much they would pay for a gallon of that liquid.
Students should note that most of these liquids probably
are not sold by the gallon.
5. Now the students must research the accuracy of their
each liquid (usually at the bottom of the front label in
small numbers). They must record the amount of liquid
being sold as one unit (milk = 1 gallon, bottled water =
18 oz., etc.). Use the “Price Is Nice” card at each station
6. Let the students know how much time remains,
make “buzzer” noises if a student records their data
incorrectly. Clarify the rules and equations as needed.
7. After the time has expired, each student or group
should have calculated a price for the different liquids.
Have the students discuss how their guesses compare
to the calculated answers. Find out which student had
the closest guess, and get a game show style round of
applause for him or her. The “Price Is Nice” labels can
have the correct calculated price on the back, which can
be revealed by students for a more “game show” feel.
8. As the students discuss their thoughts on the prices,
they may consider:
Tap water costs only a few cents per gallon.
Bottled water costs a lot more than they thought
per gallon!
Different collections of liquids will inspire
different thoughts.
130$&%63&
1. Create 5 stations around the room. At each station,
leave a container of one of the liquids (e.g., the small
bottle of water next to the Bottled Water station).
2. Place the “The Price Is Nice” cards for each liquid
next to it. Cover the cards so that the price of each
gallon is hidden.
3. The students are now contestants on the game show
“The Price Is Nice”! They can work on the activity in
groups or on their own.
9. Have students list the reasons they found each thing
surprising. Why does milk cost more than gasoline?
Why does bottled water cost so much more than tap
water?
between bottled water and tap water, they are ready to
move on to the next activity.
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Students will investigate bottled water and tap water
to explore the price difference that they noticed. Each
student will be given a “Tap Water vs. Bottled Water”
card. The cards contain facts about bottled water and
tap water that allow students to compare and contrast
different water sources. Students should read their own
card, and compare their card’s fact with those of other
students. Students will analyze any changed opinions
or new understandings that they gain from these facts,
including the similarity in water quality between tap
and bottled water, despite price differences
."5&3*"-4
Tap Water versus Bottled Water data cards
As many different water bottles from different
130$&%63&
1. Keep all the water bottles together. Pass them around
the room during this part of the activity.
2. Move the gallon of tap water and a single bottle of
bottled water to the front of the room; remove the other
liquids so that they are no longer the focus.
3. Have students focus on the question “Why does
bottled water cost more than tap water?” Allow time
to brainstorm possible answers for a few minutes;
encourage discussion with a neighbor.
4. Each student needs to write down what they consider
the “#1 reason” bottled water costs more than tap water.
5. Have students share their reasons. Create a tally
of student ideas that are similar. You can write their
answers up on the board (see table). The tally will keep
track of which reasons are most popular. Make sure that
each student gets to vote! Create as many categories
category. (For example, “bottled water is in plastic
bottles” would be the same as “bottled water uses
plastic.”)
6. Give each student a Tap Water versus Bottled Water
data card. Students should read their card and then
circulate around the room to compare cards with other
students. They should keep track of which ideas are
most surprising or interesting to them.
7. After several minutes, have students return to their
seats. Students may want to change their votes after
reading the data cards. Create a new column on the
right of the table and create a new tally of votes.
8. Students should see some changes to the class’
opinions after considering the facts. Let students
discuss which facts were most interesting and why.
Bottled water uses plastic.
Tap water is sold in bulk.
Bottled water is purer.
Bottled water is transported farther.
FIRST TALLY
Bottled water uses plastic.
Tap water is sold in bulk.
Bottled water is purer.
Bottled water is transported farther.
SECOND TALLY
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Students will examine the chemistry behind the pufocus on different properties of water that need to be
various properties, students will focus on acid and base
chemistry, including water pH.
."5&3*"-4
“The pH Scale” diagram with labels
“Dissociation” diagram
130$&%63&
1. Let students know that they were investigating bottled water and tap water for a reason: the issue of purity.
People drink bottled water for a variety of reasons:
they believe it tastes better than tap water, they believe
it’s safer than tap water, they believe it to be purer than
tap water, it is available and more convenient than tap
water.
2. Tap water is tested for far more contaminants than
bottled water is, giving a stronger guarantee that tap
water is safe. Bottled water is often given additional
clarity, taste, or smell.
3. Ask students to brainstorm what treatment plants
remove from water after it is taken from lakes,
reservoirs, and other sources.
Students will probably have lots of ideas, such as:
waste, and many other things. Ask students to be
in water. Make a list of potential contaminants and
Eventually, lead students to consider the acidity
Instead of saying that a liquid is just “too acidic
to drink,” we have a way of actually measuring
(quantifying) the acidity. This is measured as the
“pH” of a liquid. Liquids with some pH values are
too acidic and unsafe to drink; other liquids have
pH values that are too basic and unsafe to drink.
Whether it has a safe pH level is not the only
thing we need to know about our drinking water.
Make sure students know that there are other
contaminants that can make water unsafe.
Scientists who work at water and wastewater
treatment plants closely monitor water’s pH, to
make sure it’s safe when it’s released from the
plant.
4. Show the “pH Scale” to students, and ask students to
describe it. Some important observations to make are:
It ranges from 0 to 14.
Pure water is at the center, or 7.
14 is “Basic.”
0 is “Acidic.”
5. Explain that pH is a way to quantify how acidic
or basic water is. The closer to 7, the more “neutral”
and pure the water. If a liquid is very acidic or basic,
it is “corrosive” or “caustic” and can cause damage to
between 6 and 8 is safe and not harmful to humans.
The students should notice that “acid” and “base” are
opposite from each other. While both strong acids and
strong bases are dangerous to humans, they are different
from each other; in some ways, they are opposites.
When an acid mixes with a base, a chemical reaction
occurs between them; they both become weaker (the
pH moves closer to 7). This is called “neutralization.”
Water treatment scientists use this property of acids and
bases to treat water that is too acidic or too basic; they
add the opposing chemical to make sure the water is
neutral—safe to drink.
that are strongly acidic or basic are harmful to
our bodies; they can even corrode many other
substances. This is an aspect of water quality that
we can study in the classroom.
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Scientists have many ways of analyzing water to make
to identify a liquid’s pH is to use a chemical called an
indicator. This is a chemical that “indicates” whether
the liquid is acidic, basic, or neutral; some indicators
also show the degree of acidity and basicity.
5. Write each group’s pH reading on the pH scale
overhead. Student groups can also send a representative
to write on the overhead.
6. Lead the students in a discussion about their liquid.
What was the pH?
The pH strips that the students have are one way to use
an indicator. The paper is soaked in several indicator
chemicals. When the indicators come in contact with
an acid or base, they change color. The degree of color
change also shows just how strong or weak the acid or
base is.
Was it an acid or a base?
."5&3*"-4
Do we have any information on the packaging that
tells us what chemical might be causing the acidity
or basicity?
“pH Scale” diagram without labels
pH strips
Paper Towels
“Common Household Liquid” reference sheet
Collection of common liquids that students
recognize. Possibilities include:
Vinegar
Lemon Juice
Milk of Magnesia
Tap Water
Anti-bacterial soap
Bleach
Tabasco hot sauce
How acidic/basic was it?
Was it surprising how acidic/basic it was? Why?
Do we consider this chemical safe? Safe on our
skin? Safe to drink?
130$&%63&
1. Put the “pH scale” on the board
2. Form the students into groups, and give each group
one of the household liquids, a pH strip, and a paper
towel. (If students have any drinks in class with them,
these can also be tested.)
3. Have each group of students use a pH strip to
check the pH of their liquid. Compare the colors of
the indicator blocks on the strip to the key on the strip
container.
4. Use the paper towels to lay the damp pH strip on and
to clean up any spills.
30
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Now that students have become expert scientists who
understand the chemistry of these different liquids, it is
their duty to help educate others about them. Students
will research a household liquid that has not been
rest of the class, students will each make a one-page
."5&3*"-4
“Informing the Public” activity sheet.
130$&%63&
1. Hand out the “Informing the Public” activity sheet.
2. Tell students they are now experts on these
chemicals, and it is their duty to help educate others.
They each need to research a different household liquid
about their chosen liquids, including the pH values,
students must share their research by making handouts
for the class.
3. If time constraints will not allow for students to do
this as a homework activity, it can also be done in the
classroom. Have a number of extra containers from
cleaners, juices, and cooking materials. Many of these
have acidic or basic qualities that students can test with
pH strips.
on the package’s label, and they can use pH strips in
class to test the pH.
32
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Water treatment scientists have a responsibility to
provide safe drinking water for the people in their
making sure that the pH level of the water is safe
for human consumption. Scientists use a number of
different tools and chemicals to measure the pH. The
students are going to simulate the way that scientists
use chemicals to help purify the water and ensure that it
is potable (safe to drink).
2. Now add baking soda (sodium bicarbonate), one
occurs, and consider what is happening to the pH.
Remember that baking soda is a base! As the solution
becomes a dark greenish blue, it is becoming more and
more basic, with a higher and higher pH.
."5&3*"-4
Grape Jelly
Vinegar
Baking Soda
Distilled Water
Cups
Spoons
3. Strongly basic solutions are not potable. If we want
to make this water safe to drink again, how could we do
In an earlier activity, the students used pH strips to
measure the pH of different liquids. These strips
are soaked in a chemical called an “indicator.” pH
indicators are a variety of chemicals that can shows
differences in the pH of a solution, usually with a
distinct visual color difference.
While they are useful for determining absolute pH
values, pH strips can be costly. Fortunately, many
inexpensive indicators can be found in the grocery
store. These indicators are not as easy to determine
absolute pH with, but can be easily used to monitor
encountered are grapes. The purple color of a grape
present in most grape products, including grape juice
and grape jelly. In this activity, students will alter the
pH of a solution by adding a base and an acid to it; they
will monitor the change in pH by using grape jelly as an
indicator.
36
130$&%63&
1. Give each student (or group of students) a cup of hot
water. The students should scoop out several spoonfuls
of grape jelly into the hot water, and stir until dissolved.
Make sure that students consider the color (currently
a light/dark purple) and pH of the water. Grapes are
slightly acidic, so the pH is close to 5.
when in the same solution, combining in a reaction that
produces neutral water.
4. Students should add vinegar (acetic acid), one spoon
at a time. The reaction is immediate and visual. Make
sure to go slowly to avoid a mess! As students add each
spoonful, observe the color change that takes place.
5. Water scientists perform a similar process to this
when they are treating water; part of the treatment
process ends up making the water very acidic. Before
the water is fully treated, a strong base must be added to
neutralize the acid and make the water safe to drink.
6. Their wet-lab challenge is to perform this process of
making a solution reach a certain acidic pH, and then
use a base to neutralize the acid and return it to a safe
pH. In this challenge, however, they will not be using
grape jelly; they will be using pH strips or a digital pH
meter.
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Students will consider the methods used to monitor
water pH, including various indicators. Using a new
indicator—a compound from grapes—students will
monitor changes to the pH of a liquid. Students will
alter the pH by adding a strongly basic compound and
a strongly acidic compound. Through this activity, they
will simulate part of the water treatment process at a
water treatment plant.
130$&%63&
1. Review: pH, acids, bases, water treatment, dissociation, neutralization.
2. Explain story: scientists at a water treatment plant
need to treat incoming reservoir water to prepare it for
drinking. You are in charge of monitoring the pH of the
water and adjusting it during treatment.
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cups and beaker appropriately as acid (lowest pH), base
(highest pH), and untreated water (most neutral pH.)
Fill in the data table with the initial pHs.
2 small plastic cups
1 small beaker
Dilute vinegar solution
Dilute bleach solution
Distilled water
2 Disposable pipettes
pH strips
5. Label one pipette as “Acid” and the other as “Base.”
other is to be used solely with the base sample.
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6. Using the pipet, add 1 mL of acid to the water,
monitoring the pH after each mL is added. Repeat
until the pH reaches or passes the chosen low pH limit.
Keep track of the amount of acid added in the data
table.
2. Record the pH, and choose a low and high pH for
students to reach during the lab.
7. Using the pipet, add 1 mL of base to the water,
monitoring the pH after each mL is added. Repeat until
the pH reaches or passes the chosen high pH limit.
Keep track of the amount of base added in the data
table.
1. Use a pH strip to test the pH of the dilute vinegar
(acid solution) and dilute bleach (base solution). Adjust
the concentration so that the vinegar pH is close to 3
and the bleach pH is about 11.
3. Example: if the vinegar is 3 and the bleach is 11, students should lower the water’s pH to 4, and raise it to 8.
Set out 2 disposable pipettes.
13&1"3"5*0/1&345"5*0/
1. Set out a one cup, then the beaker, and the second
cup in a row.
8. Remember that the water is still not potable, as this
is only a simulation. What other steps would need to be
Complete the rest of the data sheet.?
at least 2 cm. Fill the second cup with bleach solution
to a depth of at least 2 cm. Fill the beaker with distilled
water to a depth of at least 2 cm.
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When water is present in solution, some of its
molecules will break up, or dissociate, into two ions:
H+
. These ions are highly reactive and can be
used to outline the underlying chemistry of acids and
bases. pH is determined by measuring the activity and
presence of H+ ions.
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“Dissociation” transparency
Vinegar
Baking soda
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1. Make sure that students are familiar with the
molecular nature of matter, and that water is described
as H2
solution, the two ions will combine into H2
a neutralization reactions. Mixing these two solutions
is also likely to produce other products as well. This
can be demonstrated with vinegar and baking soda.
Vinegar, in solution with water, has many H+ ions. By
ions, the neutralization
reaction takes place, producing the H2
compounds. In this vinegar and baking soda reactions,
carbon dioxide gas is one of the other products. With
a lower concentration of H+ ions now that some have
been combined into H2
neutral value of 7.
9. In the wet-lab, students will perform this same
process on a sample of water. They will add acids and
bases to adjust the pH, and use pH strips or meters to
monitor the pH as they perform the lab.
2. Now consider the reasons that acids and bases
are intrinsically linked to water chemistry. Show
the “Dissociation” transparency. Explain that in any
water-based solution, the water molecules occasionally
+
dissociate from H2
.
In an acid, there are more H+
The more H+ ions, the more acidic the solution is.
ions than H+ ions.
ions, the more basic the solution is.
-
-
In pure water, the positive H+ ions and the negative
ions are in balance. This is the neutral pH of 7.
6. While dissociation is a source of H+
-
ions in
of the solution. In pure water, the H+
ions that
result from dissociation are at a low concentration and
balance each other so that the solution is neutral.
7. The addition of other compounds is usually the
source of most of the H+
ions in an acid or
base. For instance, acids such as vinegar have extra
H+ molecules that they contribute to the solution. And
-
molecules to the solution.
-
rich solution mixes with an H+ rich
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To connect the students’ understanding of chemistry
environment, students can consider the scientists,
facilities, and techniques involved in purifying water.
Students will now consider the way water treatment
scientists use chemicals to help purify the water, and
simulate the change in pH on a solution based on which
chemicals are added.
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Dissociation transparency
pH scale without labels transparency
Dissociation tags for students
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1. Create a large pH scale that students can maneuver
on by displaying the pH transparency on the board or
wall. Alternatively, this can be done by drawing a pH
scale on the board with markers.
a very strong base, to bring the pH to a safe level. This
has a pH of about 14! Add a single student to the mix
cutouts stuck to him to make the
group of students slightly basic. A little bit of a very
should be around a pH of 8, where water treatment
plants consider it safe for drinking.
7. Students can then remove their tags. It can be helpful
to count them out, and match up H+
tags, then
replace them with H2
tags leftover to show the resulting slightly basic pH.
8. In the wet lab, they will perform this same process
on a sample of water. They will add acids and bases to
adjust the pH of the water sample, and use pH strips or
meters to monitor the pH as they partner on the lab.
2. Cut out the dissociation tags for H+
, and H2
These will be held by students to show their acidity or
basicity. Alternatively, attaching tape to the back of
these lets them be attracted to the students.
3. Place several students with H2
They represent the reservoir water that is taken into the
water treatment plant. While it is at a safe pH of 7, it
has many other impurities that scientists need to clean
aluminum sulfate (alum). This is used to help remove
larger material in the water (sediment and organic
material). This chemical is highly acidic, with a pH of
about 2. Add some students with all H+ cutouts, and
have the entire group of students slide together to the
more acidic end of the scale, approximately 2.5.
toxic chemicals and bacteria are removed. Remove
keep the solution acidic at 2.5.
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In addition to treating water before it is given out to the
public, water treatments scientists also have to treat water after people use it.
3. Place an empty gallon jug next to it, open and with a
funnel on top. This will be the students’ drain to collect
and view the wastewater.
After humans have used the water, it is called “wastewater.” Ask students to brainstorm some ideas of what
is included in waste water; some possible answers
included soap/detergent, kitchen scraps and waste, human waste (urine and feces), runoff from roads and
parking lots, industrial waste, anything that goes down
the drain!
3. Have students add the waste materials one at time.
They can rotate though, one by one or as groups, adding
all the materials. Students should crush up any larger
items (such as snack crackers) to get them through the
funnel. Use the gallon of water to wash the materials
down into the jug, but make sure there is enough water
to use for each step.
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4. When all the material is added, the students can make
observations about the gallon of wastewater.
Reusable
An empty gallon jug
Half a gallon of water
A funnel
“Waste”
Soil
Dishwashing soap
Vegetable oil
Yeast
Filtration
Paper towels
Plastic cups
Sand
Tea Strainers
Filter charcoal
pH test strips
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1. Tell students that they are going to perform an activity now to help them understand what the water treatment scientists do to help treat wastewater. To start,
let’s think about the water we use in the home. The students will act as an ordinary household, washing items
down the drain in a normal day.
5. Now students have the task of cleaning up the wastethe dirty water to make it as pure as possible. Show
sand, strainers, charcoal, and more). Using these tools,
they need to try to purify the water.
6. Give each student group one small plastic cup of wa7. Each group should record the status of the water
to purify it. They can record the change in water quality
on this sheet; this includes water odor, color, appearance, and pH.
keep processing their sample of the water. The last 10
minutes can be used for cleanup of materials and the
attempts.
9. Whose water looks the clearest (and has the best
pH)? What methods did they use? Did anything in particular work well?
2. Fill a gallon jug with water and place it at the front
of the room. This will be the students’ water to wash
things down the drain.
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