Ch. 3: Water and the Fitness of the Environment Notes

Emma Cress
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Notes on Ch.3 Water and the Fitness of the Environment

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Page 1

3.1 The Polarity of Water Molecules Results in Hydrogen Bonding

Vocabulary: Polar Molecule --> A molecule with opposite charges on different ends of the molecule. Hydrogen Bonding --> A weak bond between the positive hydrogen atom of one molecule and the negative pole of another molecule. 

 Study Questions: Why is water considered polar? Water is considered polar because there is a greater density of electrons at any given time surrounding the oxygen atom of H2O than the hydrogen atoms. Therefore, the oxygen end or pole is more negative than the hydrogen end or pole. (Image 1 represents the polarity of a water molecule) Explain hydrogen bonding. A hydrogen bond forms when the slightly positively charged hydrogen pole/area/atom of one molecule is attracted to the slightly negatively charged pole/area/atom of another nearby molecule (Image 2 represents hydrogen bonding in action) How many hydrogen bonds can a single water molecule form? Four, there are two hydrogen atoms which can form hydrogen bonds with one oxygen each and the oxygen can form two hydrogen bonds with two different hydrogens from molecules. (This concept is shown in image 2)

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3.2 Four Emergent Properties of Water Contribute to Earths Fitness for Life

Vocabulary: Cohesion --> The binding together of like molecules, often through hydrogen bonds. Adhesion --> The attraction between different molecules. Kinetic Energy --> Essentially, the energy of motion.... energy while in motion. Heat --> Also known as thermal energy. The most random form of energy and the total amount of kinetic energy of an object. Temperature --> The intensity of heat in degrees. Calorie (c) -->  The amount of heat energy required to raise the temperature of 1g of water by 1-degree Celsius. Kilocalorie (C) --> The calories used to measure energy in food. 1 Kilocalorie == 1,000 calories. Joule --> The SI unit of work or energy. (1 Joule = .239 calories ; I calorie == 4.184 Joules.) Specific heat -->  The amount that must be absorbed or lost for 1g of a substance to change its temperature by 1-degree Celcius.  Evaporative Cooling --> The process in which the surface of an object becomes cooler during evaporation. (owing to the change of molecules with the greatest Kinetic energy from a liquid to a gas) Solution --> A liquid that is a homogeneous liquid of two or more substances. Solvent --> The dissolving agent of a solution. Solute --> A substance that is dissolved in a solution. Aqueous Solution -->  A solution in which water is the solvent. Hydration Shell -->  The sphere of water molecules around a dissolved ion. Colloid --> A mixture of a liquid and particles that, (because of their size) remain suspended, rather than dissolving in liquid. Hydrophobic --> Having an aversion to water Hydrophilic --> Having an infinity to water. Molecular Mass --> The sum of the masses of all the atoms in a molecule. Mole / Mol --> The number of grams of a substance that equals its molecular weight in electrons and contains Avogadro's number. Molarity --> A common measure of solute concentration, refers to the number of moles of solute per liter.

~ Water Has 4 Emergent Properties ~ Cohesion --> Water binds itself together through hydrogen bonds. Moderation of Temperature -->  Expansion upon Freezing --> Solvent of Life -->

Cohesion:   (the binding together of like molecules, often through hydrogen bonds) Important Concepts: Water Transport in Plants Evaporation from leaves pulls water upward from the roots through water-conducting cells. Hydrogen bonds cause water molecules leaving the veins to tug on molecules further down and the upward pull continues all the way down through the roots. Walking on Water The high surface tension of water, resulting from the collective strength of its hydrogen bonds, allows animals such as the water strider to walk on water.  

Moderation of Temperature:  Heat and Temperature --> The amount of heat in a given body of matter is the average kinetic energy of the object and dependent in part upon the volume of the object. The amount of temperature of a given body of matter is dependent on the intensity of the average kinetic energy of the object and has no regard to the volume. Important Concepts: Achieving Equilibrium When an object of a higher heat mixes with one of a lower heat, the cooler objects' molecules take energy from the object of higher heat and its molecules speed up (resulting in higher kinetic energy) at the expense of the object of greater heat. Atoms and Molecules Atoms and Molecules have kinetic energy because they are constantly moving.   Waters High Specific Heat --> (Specific Heat:     the amount of energy required to raise 1g of a substance by 1 degree Celcius) The specific heat of water is 1 calorie per gram per degree Celsius, abbreviated as 1 cal / g / degree Celcius  \ The high specific heat of water is due to hydrogen bonding, heat is only energy and it takes a lot of energy to break every hydrogen bond in a sample of water to raise the temperature. Due to the excessive energy required to break hydrogen bonds, water can absorb much more heat before rising in temperature. Important Concepts: Resisting Temperature Change Specific heat can be thought of as a measure of how well a substance resists changing its temperature when it absorbs or releases heat.  Water is really good at resisting changes in temperature due to hydrogen bonds. When it does change its temperature it absorbs or loses a relatively large quantity of heat for each degree of change. Oceans and Large Bodies of Water A large body of water can absorb and store a huge amount of heat from the sun in the daytime and during summer while only warming up a few degrees. At night and during the winter the gradually cooling water warms the air. (Because of this, costal areas tend to have milder climates than inland regions.) Ocean temperatures tend to also be more stable due to the immense amount of heat required to raise their temperatures by even a degree. Organisms Due to organisms being made primarily of water, they are more able to resist changes in their own temperature than if they were made of a liquid of a lower specific heat.   Evaporative Cooling -->  (Evaporation:   the process of a substance in a liquid state transforming into one of a gaseous state due to an increase in temperature or pressure)    

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3.3 Acidic and Basic Conditions Affect Living Organisms.

Vocabulary: Acid --> A substance that increases the concentration of hydrogen ions in a solution. Base --> A substance that decreases the concentration of hydrogen ions in a solution.  pH --> a measure of hydrogen ion concentration, equal to -log[H+]  and ranging in value from 0 to 14.  Buffer -->  A substance that consists of acid and base forms of a solution and that minimizes changes in pH when extraneous acids or bases are added to the solution.  Acidic Precipitation --> Rain, snow, or fog that is more acidic than pH 5.2 Dissociation --> the splitting of a molecule into smaller molecules, atoms, or ions, especially by a reversible process.

Water's Ions: When water disassociates we get a hydronium (H3O+) and hydroxide ion (OH-) (We abbreviate (H3O+) as simply (H+) and call it a hydrogen ion) An acid is a substance that increases the number of hydrogen ions in a solution. Therefore, a solution that is more acidic will have more hydrogen ions and fewer hydroxide ions. A base will have more hydroxide ions and fewer hydrogen ions.   You can see the process of disassociation in the figure below:

pH and the pH scale: Since pH is logarithmic, each numerical change represents a 10X change in ion concentration. Therefore, a pH of 3 is 20X more acidic than a pH of 5 and a pH of 12 is 40X more basic than a pH of 8. Values that have a low pH value are more acidic. Values with a high pH value are more basic. A value of 7 on the pH is considered to be neutral.

Acid Precipitation: Cause:  Buring of Fossil Fuels Oxide and CO2 Emissions Natural causes such as volcanoes releasing pollutants. This leads to an increase of CO2 in the air, causing an acidification of the moisture in the air and therefore when that moisture leaves the clouds as precipitation, that precipitation is more acidic. Effect:  Soil damage -- absorbs vital nutrients from the soil before plants can use them. Tree damage at higher elevations. Acidification of lakes, ponds, streams, rivers, wetlands, and oceans -- kills marine life, damages ecosystems. About 30% of all CO2 in the atmosphere gets absorbed by our oceans, causing our ocean temperatures to rise and the water to become more acidic. This severely damages a variety of organisms and ecosystems, especially coral reefs, which rely on calcification to survive, acidic water destroys this calcification and prevents coral from growing and surviving.

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