Chapter 3: Water and the Fitness of the Environment

Chapter Summary

Concept 3.1 The polarity of water results in hydrogen bonding

Water is the basis of all life and is so common and needed that it sometimes can be overlooked and under appreciated. It has a unique behavior with molecules and is studied for such. Once studied, the water molecule can be proven to be very simple. It is shaped like a wide V, with its two hydrogen atoms joined to the oxygen atom by single covalent bond. These are bonds that are called polar covalent bonds, which mean that because oxygen is more electronegative than hydrogen, the electrons of the covalent bonds spend more time closer to oxygen than hydrogen. This unequal distribution of electrons makes water a polar molecule, which means that the two ends of the molecule, has opposite charges. The oxygen part of the molecule is a partial negative charge, while the hydrogen end of the molecule has a partial positive charge. Defining properties of water arise from attractions between its polar molecules: the opposite ends of the molecule attract. This in turn means that this is held together by a hydrogen bond. But when water is in normal liquid form its hydrogen bonds are very fragile. As a result of this these bonds break and re-form constantly. It’s so fragile in fact that it only last a few trillionths of a second, but new bonds are being formed form other partners. This means, at any instant, many of all the water molecules are bonded to their hydrogen-bonded neighbors. These amazing qualities of water are emergent properties resulting from the hydrogen bonding that orders molecules into a higher level of structural organization. (see figure one for hydrogen bonds between water molecules example).

3D_model_hydrogen_bonds_in_water.jpg
Figure one
Concept 3.2 Four emergent properties of water contribute to Earth's fitness for life

This concept will go through the four properties that contribute to the Earth's fitness for life, which are: cohesive behavior, ability to moderate temperature, expansion upon freezing, and versatility as a solvent.

Cohesion

The linkages between hydrogen bonds is a phenomenon called cohesion. Cohesion due to hydrogen bonding contributes to the transport of water and dissolved nutrients against gravity in plants. The water is absorbed by the plants into their veins, and when the water evaporates from a leaf, hydrogen bonds cause water molecules leaving the veins to tug on molecules farther down, and the upward pull is transmitted through the water - conducting cells all the way to the roots. Adhesion, the clinging of one substance to another, also plays a role. The adhesion of water to cells walls by hydrogen bonds helps the downward pull of gravity. Something related to cohesion is surface tension, a measure of how difficult it is to stretch or break the surface of a liquid. At the in between of water and air is an ordered arrangement of water molecules, which are all hydrogen - bonded. This is as if the water has an invisible film over it. For example- some animals can stand, walk, or run on water without breaking the surface. (see figure two).


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Figure two Walking on water.





Moderation of Temperature

Water moderates air temperature by absorbing heat from air that is warmer and releasing the stored heat to air that is cooler. Water is also an effective heat bank because of its absorption ability. For further understanding heat and temperature will be discussed.

Heat and Temperature

Anything that moves has kinetic energy, the energy of motion. atoms and molecules have this because they are in constant motion that doesn't seem to go in any particular direction. The faster it goes the more kinetic energy. Heat is a form of energy. Heat depends in part on the matters volume because it measured in total kinetic energy. Although heat is related to temperature, they are not the same thing. Temperature is a measure of heat intensity that represents the average kinetic energy of the molecules, regardless of volume. When water is heated the molecules speed increases which means that the water is hot. Remember the greater the volume the greater the heat held within. Whenever two objects of different temperature are combined heat passes from the warmer object to the cooler object until the two are the same temperature. Molecules of the cooler object speed up because of the warmer one. Throughout this explanation the Celsius scale will be used to measure temperature. At sea level, water freezes at 0 degrees Celsius and boils at 100 degrees Celsius. The temperature of the average human body is 37 degrees Celsius, and a comfortable room temperature is 20-25 degrees Celsius. One convenient unit of heat used in this explanation is the calorie. A calorie is rise in temperature. While it is also the opposite. A kilocalorie is 1,000 calories which is the quantity required to raise the temperature of 1 kilogram of water by 1 degree Celsius. Another unit is a joule which equals 0.239 calories; and one calorie is 4.184 joules.

Water's High Specific Heat

Water's ability to maintain temperature is because it has a relatively high specific heat. The specific heat of a substance is defined as the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by one degree Celsius. Therefore, the specific heat of water is one calorie per gram per degree Celsius. Because of waters high specific heat water will change its temperature less. Specific heat is best thought of as a measure of how well a substance resists changing its temperature when it absorbs or releases heat. Hydrogen bonding is a good comparison to specific heat. Heat must be absorbed in order to break down hydrogen bonds, and heat is released when hydrogen bonds form. Water helps in the real world with specific heat because: for example it can control climates with the release of heat in huge bodies of water. It can also regulate coastal temperatures as well.

Evaporative Cooling

Evaporative cooling is based on water's high heat of vaporization, which is the quantity of heat a liquid must absorb for 1 g of it to be converted from the liquid to the gaseous state. The evaporative loss of the most energetic water molecules cool a surface. Another word of thought and importance: evaporative cooling- this occurs because the hottest molecules, those with the greatest kinetic energy, are most likely to leave gas.


Insulation of Bodies of Water by Floating Ice

Hydrogen bonding is also responsible for ice forming on the surface of water which in short means water solidifies and expands. Hydrogen bonds move slow when something is solid or frozen. And when water is in normal state they slowly move back and forth, and so on and so fourth. Ice floats because it is less dense than liquid water. This allows life to exist under the frozen surfaces or lakes and polar seas. Also, when hydrogen bonds are stable they are frozen. and liquid water has motion bonds are broken.
Ice bond
Ice bond
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Water bond




The Solvent of Life


A liquid that is a completely homogeneous mixture of two or more substances is called a solution. The dissolving agent of a solution is the solvent, and the substance dissolved is the solute. An aqueous solution is one in which water is a solvent. Nothing in the world is a better solvent than water, this holds true to this day. Although it is not a universal solvent. But water is also a very versatile solvent as well. Suppose fore example, that a spoonful of table salt, the ionic compound sodium chloride, is placed in water. At the surface of the crystal's of salt the ions are exposed to the solvent. These ions and the water molecules have a mutual affinity owing to the attraction between opposite charges. The oxygen parts are negatively charged and cling to sodium cations. While the hydrogen regions are positively charged and are attracted to chloride anions. As a result, water molecules surround the individual sodium and chloride ions, separating and shielding them from one another. The sphere of water molecules around each dissolved ion is called a hydration shell. Water eventually dissolves all the ions. The result is a solution of two solutes, sodium cations and chloride anions, homogeneously mixed with water, the solvent. Also, a compound does not need to be ionic to dissolve in water. Water is the solvent of life.


Any substance that has an affinity for water is said to be hydrophilic. In some cases, substances can be hydrophilic without actually dissolving. Substances that are non ionic and non polar actually seem to repel water; which is known as being hydrophobic. These substance do not have an affinity for water.

Solute Concentration in Aqueous Solutions

We know, the mass of each atom in a given molecule, so we can calculate its molecular mass, which is simply the sum of the masses of all the atoms in a molecule. Also, for measurement of the amount of a substance we use moles. Using moles has an advantage because it gives exact amounts. And finally molarity is the number of moles of solute per liter of solution.

Concept 3.3 Acidic and basic conditions affect living organisms

A water molecule can transfer an H+ to another water molecule to form H3O+ (represented by H+) and OH-.

3b4a852144bff98214ea23dcd8287afd-3.png
Equation of statement above



Effects of Changes in pH

Acids and Bases

An acid is a substance that increases the hydrogen ion concentration of a solution.
A base is a substance that reduces the hydrogen ion concentration of a solution.

The pH Scale

The concentration of H+ is expressed as pH, where pH = -log [H+]. Buffers in biological fluids resist changes in pH. A buffer consist of an acid-base pair that combines reversibly with hydrogen ions.
Example of an pH scale
Example of an pH scale



















Threats to Water Quality on Earth

Fossil fuels burn and emit into the atmosphere and oxides contaminate the environment which increase CO2 amounts. When this occurs some go into the ocean and, lowering the pH and potentially affecting the calcification rate of coral reefs.


Vocabulary
Examples in summary's/ web sites.
polar molecule-which means that the two ends of the molecule, has opposite charges.

The linkages between hydrogen bonds is a phenomenon called cohesion.

Adhesion-the clinging of one substance to another.

surface tension-a measure of how difficult it is to stretch or break the surface of a liquid.

Anything that moves has kinetic energy, the energy of motion.

Heat is a form of energy.

Temperature is a measure of heat intensity that represents the average kinetic energy of the molecules, regardless of volume.

calorie-A calorie is rise in temperature.

Another unit is a joule which equals 0.239 calories; and one calorie is 4.184 joules.

A kilocalorie is 1,000 calories which is the quantity required to raise the temperature of 1 kilogram of water by 1 degree Celsius.

The specific heat of a substance is defined as the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by one degree Celsius.

heat of vaporization-which is the quantity of heat a liquid must absorb for 1 g of it to be converted from the liquid to the gaseous state.

evaporative cooling- this occurs because the hottest molecules, those with the greatest kinetic energy, are most likely to leave gas.

A liquid that is a completely homogeneous mixture of two or more substances is called a solution.

The dissolving agent of a solution is the solvent, and the substance dissolved is the solute.

An aqueous solution is one in which water is a solvent.

The sphere of water molecules around each dissolved ion is called a hydration shell.

Any substance that has an affinity for water is said to be hydrophilic.

Substances that are non ionic and non polar actually seem to repel water; which is known as being hydrophobic.

molecular mass-which is simply the sum of the masses of all the atoms in a molecule.

molarity is the number of moles of solute per liter of solution.

An acid is a substance that increases the hydrogen ion concentration of a solution.

A base is a substance that reduces the hydrogen ion concentration of a solution.

Animations and videos
chapter summary:
http://www.slideshare.net/pisgahscience/water-and-the-fitness-of-the-environment
Hydrogen bonding:
http://www.youtube.com/watch?v=lkl5cbfqFRM
Adhesion, cohesion, and surface tension:
http://www.youtube.com/watch?v=OuDP9-TA7dg
Heat and temperature:
http://www.youtube.com/watch?v=PHzT7uMFEbE
Water's high specific heat:
http://www.youtube.com/watch?v=u9Qynzgu4og
Acids and bases:
http://www.youtube.com/watch?v=dzXeb_jm9sQ
http://www.youtube.com/watch?v=uZ_uKZtOpA4&feature=related
Ph scale:
http://www.youtube.com/watch?v=M8tTELZD5Ek

On-line lessons

http://mansfield.osu.edu/~sabedon/campbl03.htm
http://www.pleasanton.k12.ca.us/avhsweb/thiel/apbio/notes/chp3_notes.html

Test or Quizzes

http://www.dotsonscience.com/apbio4.pdf
http://www.hbwbiology.net/quizzes/ch3-water-chemistry.htm

News Stories

http://www-pub.iaea.org/mtcd/publications/newsletter.asp?id=89

Other relevant Web Sites

http://www.google.com/#sclient=psy&hl=en&source=hp&q=water+and+the+fitness+of+the+environment&aq=0&aqi=g5&aql=&oq=water+and+the+fitnes&pbx=1&bav=on.2,or.r_gc.r_pw.&fp=9651d7334bd74320