Station 1 - Properties of Water
pH
pH is the measure of how acidic/basic water is. Water molecules have a tendency to ionize.
They separate into ions, which are charged particles, hydrogen ions (H+) and hydroxide
ions (OH-). In pure water a very small number of water molecules form ions in this way. A
neutral solution contains an equal number of hydroxide ions and hydrogen ions. A solution
with a greater concentration of hydrogen ions (H+) is said to be acidic. A solution with a
greater concentration of hydroxide (OH-) ions is said to be alkaline or basic.
So pH litmus papers can measure how acidic/basic a sample of water is. The range for a pH
scale goes from 0 - 14, with 7 being neutral. pHs of less than 7 indicate acidity, whereas a
pH of greater than 7 indicates a base. Since pH can be affected by chemicals in the water,
pH is an important indicator of water that is changing chemically.
pH affects many chemical and biological processes in the water. For example, different
organisms flourish within different ranges of pH.
Materials: 4 beakers with samples of distilled water, tap water, pond water and reef salt
water, 4 strips of litmus paper and a pH scale
Directions: Dip one of the strips of litmus paper into the beaker of distilled water for a few
seconds, then lay the strip on a paper towel. Repeat using a new strip of litmus paper for
each water sample. Compare the strips color to the pH scale and record the estimated pH
value for each sample of water.
Which sample had a high or more basic pH value?
Which sample had the lowest or more acidic pH value?
Did any of the samples show to have a neutral pH near 7?
Clean up: Place the used litmus papers in the indicated beaker. Leave everything else the
way it was.
Station 2 – Properties of Water
Universal Solvent
Scientists often call water the “universal solvent” because water can dissolve
more substances than any other liquid. Some substances, like common table
salt (sodium chloride, NaCl), dissolve in water very easily. When placed in
water, sodium chloride molecules fall apart. The positively charged sodium ion
(Na+) binds to oxygen, while the negatively charged chloride ion (Cl-) attaches
to hydrogen. This makes a very stable “salty” water molecule.
This property of water allows for the transport of nutrients vital to life in animals
and plants.
A drop of rainwater falling through the air dissolves atmospheric gases. When
rain reaches the earth, it affects the quality of the land, lakes and rivers.
Materials: 2 test tubes with rubber stoppers, water, isopropyl alcohol, salt, and
small measuring spoon
Directions:
Test tube 1: There are samples of water in test tube 1, add five full scoops of
salt to one of these test tubes. Place the rubber stopper firmly into the top of
the test tube and vigorously shake the test tube to mix the salt and water. Let
the solution settle a few seconds then record your observations.
Test tube 2: There is a sample of isopropyl alcohol in test tube 2, add five full
scoops of salt to one of these test tubes. Place the rubber stopper firmly into
the top of the test tube and vigorously shake the test tube to mix the salt and
alcohol. Let the solution settle a few seconds then record your observations.
Which test tube (1 or 2) had more salt left at the bottom of the test tube?
Which liquid did the salt dissolve in better?
Clean up: Pour out the contents of your used test tubes into the sink. Carefully
rinse out the 2 test tubes and place in the used test tube rack. Rinse the rubber
stoppers and put back where they started.
Station 3 – Properties of Water
Cohesion and Adhesion
Cohesion—Water molecules are attracted to more water molecules so they
stick to each other. This is due to the hydrogen bonds among the molecules.
Water molecules like to stay close together. If you spill a cup of water on the
floor it will stay together in a puddle. Water will “bead up” or form into a
spherical shape when on a non-polar surface because the molecules are
sticking to each other.
Adhesion—Water molecules are attracted and stick to other substances.
Water will stick to other polar surfaces like glass. You can see this property
when water creeps up the inside of a drinking glass. Think of a sponge or a
paper towel used to “soak up” spilled water. This is how water makes things
wet.
Materials: One small piece of wax paper, one glass slide, beaker of water and
one pipette
Directions: Using the pipette place three drops of water on top of one another
onto the small piece of wax paper. Draw the drop of water viewed from the
side.
Then place three drops of water on top of one another onto the glass slide.
Draw the drop of water viewed from the side.
Is the bead of water on the wax paper higher or lower in height than the bead
of water on the glass slide?
Now carefully lift the wax paper and tilt it side to side. How does the water
move along the wax paper?
Then carefully lift the glass slide and tilt it side to side. How does the water
move along the glass slide?
Which surface do you think the water is more adhesive to?
On which material do you see water’s cohesive property is stronger than its
adhesive property? Why?
Clean up: Put your used wax paper and glass slide in the indicated bowl. Dry
off any wet surfaces on the counter.
Station 4 – Properties of Water
Surface Tension
Surface Tension - Water molecules at the surface have a stronger attraction to each
other than for the molecules in the air above. So the water molecules cling tightly to
each other forming what’s like a skin or invisible film at the surface. Water’s surface
tension can hold weight that would normally sink. You can carefully float a paper clip
on top of the water. Some aquatic insects such as the water strider or pond skater rely
on surface tension to walk on water. Surface tension is essential for the transfer of
energy from wind to water to create waves. Waves are necessary for rapid oxygen
diffusion in lakes and seas. Next to mercury, water has the highest surface tension of
all commonly occurring liquids.
Materials: One beaker of water, one beaker of soapy water (one drop of Dawn dish
soap in water), one beaker of isopropyl alcohol, 3 forceps (labeled to only be used with
specified container of liquid), and 3 unused rubber bands
Directions: Carefully place one rubber band in each beaker of liquid. Record
observations.
Which liquid(s) did the rubber band float on? Why?
Why did it sink in the other liquid(s)?
Clean up: Carefully remove the rubber bands making sure to use the correct forceps
that corresponds to the correct container. (Do not mix the liquids) Place the used
rubber bands in the used rubber band container. Place the forceps back in the same
location.
Station 5 – Properties of Water
Capillary Action
Capillary action is important for moving water (and all of the things that are
dissolved in it) around. It is defined as the movement of water within the
spaces of a porous material due to the forces of adhesion, cohesion, and
surface tension.
Capillary action occurs because water is sticky, thanks to the forces of
cohesion (water molecules like to stay close together) and adhesion (water
molecules are attracted and stick to other substances). Adhesion of water to
the walls of a vessel will cause an upward force on the liquid at the edges and
result in a meniscus, which turns upward. The surface tension acts to hold the
surface intact. Capillary action occurs when the adhesion to the walls is
stronger than the cohesive forces between the liquid molecules.
When you use a paper towel to clean up a spilled liquid, the liquid adheres
itself to the paper fibers and the liquid moves to the spaces between and inside
of the fibers
This can also be seen as blood moves through our capillaries, carrying
nutrients to each cell within our body.
Plants and trees couldn't thrive without capillary action. Plants put down roots
into the soil, which are capable of carrying water from the soil up into the plant.
Water, which contains dissolved nutrients, gets inside the roots and starts
climbing up the plant tissue. One of the tallest plants is the redwood tree.
Water moves from its roots to its leaves, more than 310 feet above the ground.
As a plant loses water through pores in the leaves, more water moves up from
roots and stems to replace the lost water.
Materials: Beaker of water, pencil, strip of filter paper, black and purple marker
Directions: About 3 cm from the bottom of the filter paper mark a black and
then a purple dot about 1 cm in diameter on the filter paper. Roll the other end
onto a pencil (or have someone hold it) and lower it into the water making sure
the water level is below the black and purple dots. Record observations.
What did the water do as it traveled up the filter paper?
Clean up: Dispose of your used filter paper and dry up any spilled water on the
counter top.
Station 6 – Properties of Water
Reading
Properties of Water
Like all matter, water is made up of atoms. Atoms attach together, or bond, to form
molecules. Two hydrogen atoms bonded to an oxygen atom form a water molecule. Water
has several properties that make it a very unique substance.
It has the formula H2O. When oxygen and hydrogen combine (H-O-H) they form a v-shaped
triangular molecule. While water molecules are electrically neutral, the oxygen atom holds a
small negative charge and the two hydrogen atoms hold small positive charges. Water
molecules are attracted to each other, creating hydrogen bonds. These strong bonds
determine almost every physical property of water and many of its chemical properties too.
A large part of the mass of most organisms is simply water. In human tissues the
percentage of water ranges from 20% in bones to 85% in brain cells. The water content is
greater in embryonic and young cells and decreases as aging occurs. About 70% of our
total body weight is water; as much as 95% of jellyfish or certain plants is water. Water is not
only the major component of organisms but also one of the principal environmental factors
affecting them. Many organisms live within the sea or in freshwater rivers, lakes, and
puddles. The physical and chemical properties of water have permitted living things to
appear, to survive, and to evolve on this planet. Water is the solvent, the medium and the
participant in most of the chemical reactions occurring in our environment.
Polarity - When electrons are not shared equally in a covalent bond, the molecule is
described as polar. Water molecules are polar. This means that while water molecules are
neutral as a whole, one end of the water molecule tends to have a positive charge while the
other has a negative charge. The oxygen end has a slight negative charge while the
hydrogen end has a slight positive charge. Each end of a water molecule is attracted to the
opposite charged end of another water molecule. Water's polarity is responsible for the
"stickiness" or cohesion between the molecules.
States of Matter - Water is the only known substance that exists naturally in all three states
of matter on Earth: gas, liquid, and solid. It exists in its liquid state in water bodies such as
oceans and lakes. It exists in its solid state in the Polar Regions and in glaciers. It exists in
its gaseous state in the air in the form of vapor and also clouds. Water makes up more than
two-thirds of the Earth's surface. One phase can change into another. For example, water
can evaporate to form water vapor or freeze to form ice.
No matter the phase of the water—solid, liquid or gas—the chemical composition of each
molecule is always H2O. The water molecules do not break up. The difference is in way the
water molecules are arranged and the speed at which they move. Keep in mind that water
molecules are always in constant motion, even in ice.
• In the solid phase—as ice—the molecules are packed tightly together. They move slowly.
• In the gas phase—as water vapor—the H2O molecules are farther apart. They move very
fast and spread quickly.
• In the liquid phase, they behave somewhere in between.
Thermal Properties
Water absorbs or releases more heat than many substances for each degree of temperature
increase or decrease. Because of this, it is widely used for cooling and for transferring heat
in thermal and chemical processes. Differences in temperature between lakes and rivers
and the surrounding air may have a variety of effects. For example, local fog or mist is likely
to occur if a lake cools in the surrounding air enough to cause saturation—small water
droplets are suspended in the air. Large bodies of water, such as the oceans or the Great
Lakes, have a profound influence on climate. They are the world’s great heat reservoirs and
heat exchangers and the source of much of the moisture that falls as rain and snow over
adjacent landmasses. When water is colder than the air, precipitation is curbed; winds are
reduced, and fog banks are formed. These properties of water are crucial in stabilizing
temperatures on earth.
Specific Heat—Water has a high specific heat. The amount of energy required to raise the
temperature of water by one degree Celsius is quite large. Because so much heat loss or
heat input is required to lower or raise the temperature of water, the oceans and other large
bodies of water have relatively constant temperatures. Thus, many organisms living in the
oceans are provided with a relatively constant environmental temperature. The high water
content of plants and animals living on land helps them to maintain a relatively constant
internal temperature (Ours is about 98.6oF).
The specific heat of water is 5 times greater than of sand. On a hot summer day, beach
sand may quickly warm to the point that it is too hot to stand on while ocean water warms
only a little. During the evening the temperature of sand will decrease while the temperature
of the ocean remains relatively constant.
Heat of Vaporization—Water has a high heat of vaporization. Water absorbs heat as it
changes from a liquid to a gas; the human body can dissipate excess heat by the
evaporation of its sweat. A leaf can keep cool in the bright sunlight by evaporating water
from its surface. Water’s high heat conductivity makes possible the even distribution of heat
throughout the body.
Boiling and Freezing—Pure water at sea level boils at 100C (212F) and freezes at 0C
(32F)
Water density--Water is most dense at 4C and then begins to expand again (becoming
less dense) as the temperature decreases further. This expansion occurs because its
hydrogen bonds become more rigid and ordered. As a result, frozen water (ice floats) upon
the denser cold water. The expansion of water takes place even before it actually freezes.
This explains why a pond freezes from the surface down, rather than from the bottom up. As
water temperature drops, the colder water (0-4C) where it is less dense— rises to the pond
surface. It freezes to form a lid of ice. This ice insulates the water below from the wintry chill
so that it is less likely to freeze. Organisms that inhabit the pond are able to survive the frigid
winter below the icy surface.