Period+3+Ch.+3+2011


 * AP Biology**
 * Chapter 3 Guided Reading Assignment**

1. Why is water considered a polar molecule? Water is polar because oxygen's electronegativity is much greater than the electronegativity of the two hydrogens bonded to it, so the oxygen will attract the electrons closer to it, making it slightly negative. This uneven distribution of electrons causes the molecule to be polar.



2. For each of the below listed properties of water – briefly define the property and then explain how water’s polar nature and polar covalent bonds contribute to the water special property. Include an example in nature of each property also.


 * a. Cohesion **
 * Is the "stickiness" that water is famous for. this "stickiness" is caused by the hydrogen bonding between different molecules of water and the negative oxygen and the positive hydrogen. An example of cohesion would be when you fill a cup of water passed the top and it bulges out. **




 * b. Adhesion **
 * Similarly, adhesion is the hydrogen bonding between water and other molecules. Water's polarity is also the cause of this property because it is attracted to other substances and forms weak bonds with them. An example of adhesion would be the phenomenon of the meniscus. **


 * c. Surface tension **
 * Surface tension is the tendency fora surface of water molecules to hold together, producing a surface that resists breaking. It is a result of cohesion and water's polar properties. An example of this would yet again be the ability to fill a cup of water past the brim causing a bulge of water at the top. **




 * d. High specific heat **
 * A high specific heat means that water resists change in temperature. In other words, it takes a lot of energy to heat it up when compared to other molecules, and similarly for cooling it down. Since water has a strong covalent bonds with also relatively strong hydrogen bonds, it is very hard to break apart these atoms. An example of this would be that alcohol boils faster than water, as do many other compounds. **


 * e. Heat of vaporization **
 * The heat of vaporization is the required enthalpy change, different for every compound, needed to convert a substance from its liquid form to its gaseous form. In addition, water's heat of vaporization is much larger than its heat of fusion because melting merely requires a partial disruption of the hydrogen bonding network of water whereas vaporization requires complete dissociation of the hydrogen bonds. An example of this would be when water evaporates on a hot day. **


 * f. Evaporative cooling **
 * Evaporative cooling is the cooling of temperature as a result of the evaporation of a liquid, which removes latent heat from the surface from which evaporation takes place. This is due to the fact that water has a high specific heat and absorbs heat as it exits our body. A lucid example of this is when we sweat we cool off. **



3. What is special about water and density? When water is solid it is less dense than when it is a liquid.

4. Define the following terms: a. Solute

c. Aqueous solution

d. Hydrophilic - the term for a substance that is polar and attracted to water; it will dissolve in water

e. Hydrophobic- Substances that repel water

f. Colloid - A suspension of particles in a solution.

g. Hydration shell

h. Molarity - (M) the measure of concentration of a solution that is in an aqueous state (units are mol solute/L solution)

5. Label the diagram below to demonstrate the dissociation of the water molecule and then relate this diagram to pH.




 * H2O + H2O --> H3O+ + OH- **

6. What defines an acid and a base? An acid is a substrate that increases the hydrogen ion concentration of a solution. A base is a substance that reduces the hydrogen ion concentration of a solution.
 * When water ionizes it splits into OH- and H+ (H3O+). These two substances determine the pH of substance. When they are in equal amounts the substance is neutral with a pH of 7 and when there is more H+ the solution is acidic so the pH would be <7. Therefore, when there is more OH- in the solution the substance is basic so the pH would be >7. **

7. Why are “apparently” small changes in pH so important in biology?

8. What is a buffer and write and explain the carbonic acid buffer system in human blood – yes we are back to the equation AGAIN!

9. What is acid precipitation and why is it important to living organisms? Acid precipitation is rain, snow, or sleet, or any other form of precipitation that has a pH of 5.6 or less. This acidity is caused by an excess of sulfur oxides and nitrogen oxides from the burning of fossil fuels and from other pollution. Acid precipitation is damaging to living things and can wash away minerals like Calcium and Magnesium that protect the soil. It can also lead to a toxic excess of Aluminum in drinking water and soil; plants suffer the most.