Water

     
Blake Williams
9/1/13


      During our third Honors Biology class, and for homework the prior night, we learn about all of the different properties of water. First we learned that H2O is polar, and that the reason for this is that the electrons between the oxygen and the two hydrogens atoms are not shared equally (the reason that the electrons are shared is because water is a covalent molecule). The six protons in the oxygen atom are able to pull these shared electrons with a greater force than that of the two hydrogens (for each only contains one proton).

H2O

H2O Water Molecule

Electronegativity Charges

This diagram shows that
the electrons of the two
hydrogens are being pulled
toward the oxygen atom.
This is due to the higher
number of protons in
oxygen than in hydrogen.

The water's polarity is shown in this molecular structure.

           



     We found out that a water molecule is capable of hydrogen bonding with up to four other water molecules. This is because the two hydrogen atoms can bond with two oxygens from two other water molecules, and the one oxygen is capable of bonding with two hydrogen atoms from another two water molecules, adding up to four in total. The diagrams below represent this process.

This figure represents the
attractions between two
water molecules.

The figure shows who one water molecule is capable of
hydrogen bonding with four other water molecules.

     The final properties that we learned about both involved the attractions of the water molecules. The first was cohesion, which is the attraction between the many water molecules. The second is adhesion, which is the attraction between the water molecules and another surface.

Cohesive

Hydrogen bonds hold all of the water molecule together.

Since hydrogen bonds cause the water molecules stick together,
insects such as water striders are able to walk on the surface of a
pond without breaking the surface. Their thin legs, with small spread-
out hairs which are not visible in the picture, are able to sit on top of
the hydrogen bonds. this is because their weight is spread out over a
large surface area.

A paperclip behaves the same as a water
strider when places on a surface of water
(For our class, we use a toothpick instead).

Due to cohesion, water forms a convex surface when a glass is slightly
overfilled. The cohesive forces (between the water molecules) is stronger
than the adhesion forces (between the water molecules and the outer surface
of the glass. There is a very strong surface tension in this figure, and it is due
to the fact that the water molecules on top have no water molecules above to
bond with, causing the bonds that they do make to be much stronger than any
of the bonds below.

Adhesive

Water molecules are attracted to
the toothpick.You can see the
water move up the paperclip.

Similar affect with a straw. This affect
is occurs because the water molecules
are polar, and therefore have a charge.
This charge is attracted to the charges of
the straw or other surfaces.

The water molecules can be seen moving
up the paper towel. this is due to both
cohesion and adhesion. The water molecules
are attracted to the paper towel, and also
attracted to other water molecules.

Combination

Cohesion and adhesion often work together.
In this picture, the water molecules are sticking
to the leaves, and those not in direct contact to
the leaves are sticking to the other water molecules.

The water molecules stick to the penny,
as well as to other water molecules.

The cohesion allows the water to stick together in one
continuous stream, while adhesion causes this stream to
stick to the xylem wall and rise up. As the water molecules
in the leaves are removed by transpiration, the water
molecules in the stream below rise up and take its place.

   We also discussed how water affects climate and temperature fluctuation. We learned that the reason costal areas have milder climates than adjacent inland areas is because water has a high heat capacity. It requires 3200X more energy to change water by one degree than it takes to change air by one degree. This is the same reason that ocean temperatures fluctuate much less than air temperatures on land. The water in the air breaks apart, but unlike air it is able to keep reforming. Since the molecules are not being broken apart as much, the molecular motion does not increase or decrease as much as it does in air.

     In class, we learned why ice floats on water. We learned that when the water is liquid, there is molecular motion, and the molecules are close together. But when the water freezes into ice, and the molecular motion stops, the water molecules form crystalline hexagon structures (because the angle between the two hydrogens and the oxygen is 120 degrees). These hexagon structures are more spread out, allowing more empty space between all of the water molecules. This extra empty space makes ice more dense than water, and that is why it floats.

     Near the end of class, we talked about why human sweat and dogs pant to cool themselves. We learned that by sweating, humans release heat, because when the water is release from a human's sweat glands, it is evaporated and sent into the air (evaporation=exothermic. Therefore the heat is released from the body). Since dogs do not have sweat glands, they use the water on their tongues instead. The process results in a release in heat through evaporation as well. Mr. Quick also explained to use why this process is more difficult in humidity. He said that since their is already water saturated in the air, you body cannot produce sweat for it cannot be evaporated.

    The last thing about water that I learned is that when it dissociates, it produces hydronium (H3O+), with a concentration of 10^-7 in pure water, and hydroxide (OH-), with a concentration of 10^-7 in pure water as well. Acids contain H3O+ and bases contain OH-.

     My partner for the day was Brian Christiansen, and we worked on the problems involving why a water strider can walk on water, and why water formed a convex surface when a glass was overfilled.